Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/PhysRevResearch.2.043415

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.2.043415/fulltext

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Real-time temperature monitoring inside living organisms provides a direct measure of their biological activities. However, it is challenging to reduce the size of biocompatible thermometers down to submicrometers, despite their potential applications for the thermal imaging of subtissue structures with single-cell resolution. Here, using quantum nanothermometers based on optically accessible electron spins in nanodiamonds, we demonstrate in vivo real-time temperature monitoring inside Caenorhabditis elegans worms. We developed a microscope system that integrates a quick-docking sample chamber, particle tracking, and an error correction filter for temperature monitoring of mobile nanodiamonds inside live adult worms with a precision of ±0.22°C. With this system, we determined temperature increases based on the worms' thermogenic responses during the chemical stimuli of mitochondrial uncouplers. Our technique demonstrates the submicrometer localization of temperature information in living animals and direct identification of their pharmacological thermogenesis, which may allow for quantification of their biological activities based on temperature.

DOI： 10.1126/sciadv.aba9636

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Language：English   Publishing type：Research paper (scientific journal)  

© 2020 Elsevier B.V. Time-resolved absorption spectra from the femtoscecond to sub-millisecond time regimes were recorded in order to eluciate the photoprotective mechanisms of carotenoid (spirilloxanthin) in core LH1 light-harvesting pigment-protein complexes from a purple photosynthetic bacterium, Rhodospirillum (Rsp.) rubrum. Carotenoids can prevent the production of singlet oxygen by rapidly quenching the Bchl a triplet state. Through this triplet-triplet energy-transfer reaction the carotenoid is believed to protect the biological system from exposure to excess light. We set out to investigate this paricular function in the purple bacterium, Rsp. rubrum strain S1. We also investigated Rsp. rubrum strain G9+, which is the carotenoidless mutant of Rsp. rubrum, to make sure that the carotenoid is truly playing this important role. As a result, we could demonstrate that strain S1 realizes nearly 100% excitation energy transfer from triplet Bchl a to carotenoid. In addition, we found another major excited state deactivation channel of carotenoids, which takes away excess energy directly from the singlet excited state of Bchl a and so prevents the production of triplet excited Bchl a.

DOI： 10.1016/j.jphotochem.2020.112628

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Language：Japanese   Publisher：(一社)日本臓器保存生物医学会  

細胞内温度が幹細胞機能に及ぼす影響について解説した。温度は生体分子のダイナミクスと反応性を通じて細胞活動を変化させる可能性が指摘されており、細胞内環境の非常に重要なパラメーターとして知られている。蛍光ナノダイヤモンド(FNDs)を用いた長期間測定可能な細胞内温度測定センシング技術を用いることにより、250μg/mL濃度以下のFNDsで標識された脂肪組織由来幹細胞(ASCs)は細胞毒性を示さないことが明らかになり、ASCsの再生機能(再生因子産生能、多分可能)に対してもFNDs標識による影響がないことが示された。細胞内温度技術は細胞・臓器保存や臓器移植技術の発展に寄与できる可能性が高いと思われる。

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Intracellular thermometry techniques play an important role in elucidating the relationship between the intracellular temperature and stem cell functions. However, there have been few reports on thermometry techniques that can detect the intracellular temperature of cells during several days of incubation. In this study, we developed a novel quantum thermometric sensing and analysis system (QTAS) using fluorescent nanodiamonds (FNDs). FNDs could label adipose tissue-derived stem cells (ASCs) at high efficiency with 24 h of incubation, and no cytotoxicity was observed in ASCs labeled with less than 500 mg mL(-1) of FNDs. The peak of FNDs was confirmed at approximately 2.87 GHz with the characteristic fluorescence spectra of NV centers that could be optically detected (optically detected magnetic resonance [ODMR]). The ODMR peak clearly shifted to the high-frequency side as the temperature decreased and gave a mean temperature dependence of -(77.6 +/- 11.0) kHz degrees C-1, thus the intracellular temperature of living ASCs during several days of culturing could be precisely measured using the QTAS. Moreover, the intracellular temperature was found to influence the production of growth factors and the degree of differentiation into adipocytes and osteocytes. These data suggest that the QTAS can be used to investigate the relationship between intracellular temperature and cellular functions.

DOI： 10.1039/d0na00146e

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Language：English   Publishing type：Research paper (scientific journal)  

<p>It has become clear that temperature plays a major role in many life phenomena. However, little is known about the intracellular temperature, and the relationship between regenerative function and intracellular temperature of stem cells. In this study, fluorescent nanodiamond (FND) that can be applied as an excellent quantum sensor was used for stem cell labeling. Then, the relationship between the regenerative function of stem cells and the intracellular temperature of stem cells was evaluated by a sensing the optically detected magnetic resonance (ODMR) activity of NV centers in FNDs. FNDs could label adipose tissue-derived stem cells (ASCs) at high efficiency with 24 h incubation, and no cytotoxicity was observed in ASCs labeled with less than 500 µg/mL of FNDs. The ODMR of NV centers in FNDs was confirmed at approximately 2.87 GHz with a characteristic fluorescence spectrum, and the intracellular temperature of living ASCs during several days of culturing could be precisely measured. Moreover, the intracellular temperature was found to influence the production of growth factors and the degree of differentiation into adipocytes and osteocytes. These data suggest that NV centers in FNDs can be used to investigate the relationship between intracellular temperature and cellular functions.</p>

DOI： 10.11378/organbio.27.185

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsanm.9b00614

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Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

© 2019 The Royal Society of Chemistry. We report on the sensing stability of quantum nanosensors in aqueous buffer solutions for the two detection schemes of quantum decoherence spectroscopy and nanoscale thermometry. The electron spin properties of single nitrogen-vacancy (NV) centers in 25 nm-sized nanodiamonds have been characterized by observing individual nanodiamonds during a continuous pH change from 4 to 11. We have determined the stability of the NV quantum sensors during the pH change as the fluctuations of ±12% and ±0.2 MHz for the spin coherence time (T2) and the resonance frequency (ω0) of their mean values, which are comparable to the instrument error of the measurement system. We discuss the importance of characterizing the sensing stability during the pH change and how the present observation affects the measurement scheme of nanodiamond-based NV quantum sensing.

DOI： 10.1039/c9ra02282a

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cplett.2018.09.063

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-018-33041-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

The carrier dynamics of the semiconductor photocatalyst is the essential concern to clarify the detailed mechanisms of photocatalytic water splitting reactions, which is one of the key issues of artificial photosynthesis to produce solar fuels. In this present study, time-resolved transient diffuse reflection spectra of rutile type TiO2 powder were recorded. Singular value decomposition against whole observed spectral data-set that was followed by global and target analysis has been performed for the first time. A series of examination revealed that the carriers generated in the bulk of TiO2 particle and two distinctive surface carriers are decaying with their own lifetimes. Moreover, the comparison of the measurements both in vacuum and under oxygen atmosphere suggested that the lifetime of surface holes is several tens of nanoseconds. The factors that govern the activity of photocatalyst should be precisely addressed based on thus identified spectral and lifetime features of carriers. Therefore, the present investigation is expected to open the new door to give some good hints when designing more active photocatalysts.

DOI： 10.1016/j.jphotochem.2017.10.054

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Fucoxanthin is a carotenoid that is mainly found in light-harvesting complexes from brown algae and diatoms. Due to the presence of a carbonyl group attached to polyene chains in polar environments, excitation produces an excited intra-molecular charge transfer. This intra-molecular charge transfer state plays a key role in the highly efficient (similar to 95%) energy-transfer from fucoxanthin to chlorophyll a in the light-harvesting complexes from brown algae. In purple bacterial light-harvesting systems the efficiency of excitation energy-transfer from carotenoids to bacteriochlorophylls depends on the extent of conjugation of the carotenoids. In this study we were successful, for the first time, in incorporating fucoxanthin into a light-harvesting complex 1 from the purple photosynthetic bacterium, Rhodospirillum rubrum G9+ (a carotenoidless strain). Femtosecond pump-probe spectroscopy was applied to this reconstituted light-harvesting complex in order to determine the efficiency of excitation energy-transfer from fucoxanthin to bacteriochlorophyll a when they are bound to the light-harvesting 1 apo-proteins.

DOI： 10.1039/c6fd00211k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

We report the direct integration and efficient coupling of nitrogen vacancy (NV) color centers in diamond nanophotonic structures into a fiber-based photonic architecture at cryogenic temperatures. NV centers are embedded in diamond micro-waveguides (μWGs), which are coupled to fiber tapers. Fiber tapers have low-loss connection to single-mode optical fibers and hence enable efficient integration of NV centers into optical fiber networks. We numerically optimize the parameters of the μWG-fiber-taper devices designed particularly for use in cryogenic experiments, resulting in 35.6% coupling efficiency, and experimentally demonstrate cooling of these devices to the liquid helium temperature of 4.2 K without loss of the fiber transmission. We observe sharp zero-phonon lines in the fluorescence of NV centers through the pigtailed fibers at 100 K. The optimized devices with high photon coupling efficiency and the demonstration of cooling to cryogenic temperatures are an important step to realize fiber-based quantum nanophotonic interfaces using diamond spin defect centers.

DOI： 10.1021/acsomega.7b01223

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the coupling of single nitrogen vacancy (NV) centers to ultrathin fiber-taper nanofibers by the manipulation of single diamond nanocrystals on the nanofibers under real-time observation of nanodiamond fluorescence. Spin-dependent fluorescence of the single NV centers is efficiently detected through the nanofiber. We show control of the spin sub-level structure of the electronic ground state using an external magnetic field and clearly observe a frequency fine tuning of m(S) = vertical bar +/- 1 &gt;. This observation demonstrates a possibility of realizing fiber-integrated quantum lambda-systems, which can be used for various quantum information devices including push-pull quantum memory and quantum gates.

DOI： 10.1088/0957-4484/27/45/455202

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the coupling of single nitrogen vacancy (NV) centers to ultrathin fiber-taper nanofibers by the manipulation of single diamond nanocrystals on the nanofibers under real-time observation of nanodiamond fluorescence. Spin-dependent fluorescence of the single NV centers is efficiently detected through the nanofiber. We show control of the spin sub-level structure of the electronic ground state using an external magnetic field and clearly observe a frequency fine tuning of m(S) = vertical bar +/- 1 &gt;. This observation demonstrates a possibility of realizing fiber-integrated quantum lambda-systems, which can be used for various quantum information devices including push-pull quantum memory and quantum gates.

DOI： 10.1088/0957-4484/27/45/455202

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Coupling of a single dipole with a nanofiber Bragg cavity (NFBC) approximating an actually fabricated structure was numerically analyzed using three dimensional finite-difference time-domain simulations for different dipole positions. For the given model structure, the Purcell factor and coupling efficiency reached to 19.1 and 82%, respectively, when the dipole is placed outside the surface of the fiber. Interestingly, these values are very close to the highest values of 20.2 and 84% obtained for the case when the dipole was located inside the fiber at the center. The analysis performed in this study will be useful in improving the performance of single-photon emitter-related quantum devices using NFBCs. (C) 2016 Optical Society of America

DOI： 10.1364/OE.24.015050

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Publishing Group  

By means of an ultrafast optical technique, we track focused gigahertz coherent phonon pulses in objects down to sub-micron in size. Infrared light pulses illuminating the surface of a single metal-coated silica fibre generate longitudinal-phonon wave packets. Reflection of visible probe light pulses from the fibre surface allows the vibrational modes of the fibre to be detected, and Brillouin optical scattering of partially transmitted light pulses allows the acoustic wavefronts inside the transparent fibre to be continuously monitored. We thereby probe acoustic focusing in the time domain resulting from generation at the curved fibre surface. An analytical model, supported by three-dimensional simulations, suggests that we have followed the focusing of the acoustic beam down to a ~ 150-nm diameter waist inside the fibre. This work significantly narrows the lateral resolution for focusing of picosecond acoustic pulses, normally limited by the diffraction limit of focused optical pulses to ~ 1 μm, and thereby opens up a new range of possibilities including nanoscale acoustic microscopy and nanoscale computed tomography.

DOI： 10.1038/lsa.2016.82

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Publishing Group  

By means of an ultrafast optical technique, we track focused gigahertz coherent phonon pulses in objects down to sub-micron in size. Infrared light pulses illuminating the surface of a single metal-coated silica fibre generate longitudinal-phonon wave packets. Reflection of visible probe light pulses from the fibre surface allows the vibrational modes of the fibre to be detected, and Brillouin optical scattering of partially transmitted light pulses allows the acoustic wavefronts inside the transparent fibre to be continuously monitored. We thereby probe acoustic focusing in the time domain resulting from generation at the curved fibre surface. An analytical model, supported by three-dimensional simulations, suggests that we have followed the focusing of the acoustic beam down to a ~ 150-nm diameter waist inside the fibre. This work significantly narrows the lateral resolution for focusing of picosecond acoustic pulses, normally limited by the diffraction limit of focused optical pulses to ~ 1 μm, and thereby opens up a new range of possibilities including nanoscale acoustic microscopy and nanoscale computed tomography.

DOI： 10.1038/lsa.2016.82

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINESE ACAD SCIENCES, CHANGCHUN INST OPTICS FINE MECHANICS AND PHYSICS  

By means of an ultrafast optical technique, we track focused gigahertz coherent phonon pulses in objects down to sub-micron in size. Infrared light pulses illuminating the surface of a single metal-coated silica fibre generate longitudinal-phonon wave packets. Reflection of visible probe light pulses from the fibre surface allows the vibrational modes of the fibre to be detected, and Brillouin optical scattering of partially transmitted light pulses allows the acoustic wavefronts inside the transparent fibre to be continuously monitored. We thereby probe acoustic focusing in the time domain resulting from generation at the curved fibre surface. An analytical model, supported by three-dimensional simulations, suggests that we have followed the focusing of the acoustic beam down to a similar to 150-nm diameter waist inside the fibre. This work significantly narrows the lateral resolution for focusing of picosecond acoustic pulses, normally limited by the diffraction limit of focused optical pulses to similar to 1 mu m, and thereby opens up a new range of possibilities including nanoscale acoustic microscopy and nanoscale computed tomography.

DOI： 10.1038/lsa.2016.82

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We report the measurements of charge density of tapered optical fibers using charged particles confined in a linear Paul trap at ambient pressure. A tapered optical fiber is placed across the trap axis at a right angle, and polystyrene microparticles are trapped along the trap axis. The distance between the equilibrium position of a positively charged particle and the tapered fiber is used to estimate the amount of charge per unit length of the fiber without knowing the amount of charge of the trapped particle. The charge per unit length of a tapered fiber with a diameter of 1.6 mu m was measured to be 2(-1)(+3) x 10(11) C/m. (C) 2016 Optical Society of America

DOI： 10.1364/OE.24.004672

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

For efficient interfacing of quantum emitters nano-and microcavities are important tools. Here, we introduce Bragg cavities fabricated on nanofibers. We show strain-tuning of the cavity resonance and first coupling experiments with quantum emitters.

DOI： 10.1109/CLEOPR.2015.7376410

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

A detailed numerical study using 3D FDTD simulation on the fiber Bragg grating cavity is reported in order to further improve the ultra-wide tunability over 20 nm and the enhanced spontaneous emission we recently reported.

DOI： 10.1109/CLEOPR.2015.7376535

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_1364

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Coupling of lithe emitters to the fiber Bragg grating cavity is experimentally realized and the position dependence of spontaneous emission of a single dipole coupled to the cavity is numerically analyzed using 3D FDTD.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We demonstrate successful cooling of ultrathin fiber tapers and their coupling with nitrogen vacancy (NV) centers in nanodiamonds at cryogenic temperatures. Nanodiamonds containing multiple NV centers are deposited on ultrathin fiber tapers with diameters ranging from 450-500 nm. The fiber tapers were successfully cooled down to 9 K with our special fiber mount and an optimization of cooling speed. The fluorescence coupled with the fiber tapers showed characteristic sharp zero-phonon lines of neutral and negatively charged NV centers. The present demonstration is important for the future NV-based quantum information devices and sensitive nanoscale cryogenic magnetometry.

DOI： 10.1117/12.2206144

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Other Link： http://orcid.org/0000-0002-7845-2387

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We demonstrate cooling of ultrathin fiber tapers coupled with nitrogen vacancy (NV) centers in nanodiamonds to cryogenic temperatures. Nanodiamonds containing multiple NV centers are deposited on the subwavelength 480-nm-diameter nanofiber region of fiber tapers. The fiber tapers are successfully cooled to 9 K using our home-built mounting holder and an optimized cooling speed. The fluorescence from the nanodiamond NV centers is efficiently channeled into a single guided mode and shows characteristic sharp zero-phonon lines (ZPLs) of both neutral and negatively charged NV centers. The present nanofiber/nanodiamond hybrid systems at cryogenic temperatures can be used as NV-based quantum information devices and for highly sensitive nanoscale magnetometry in a cryogenic environment. (C) 2015 Optical Society of America

DOI： 10.1364/OL.40.005702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Solid-state microcavities combining ultra-small mode volume, wide-range resonance frequency tuning, as well as lossless coupling to a single mode fibre are integral tools for nanophotonics and quantum networks. We developed an integrated system providing all of these three indispensable properties. It consists of a nanofibre Bragg cavity (NFBC) with the mode volume of under 1 mu m(3) and repeatable tuning capability over more than 20 nm at visible wavelengths. In order to demonstrate quantum light-matter interaction, we establish coupling of quantum dots to our tunable NFBC and achieve an emission enhancement by a factor of 2.7.

DOI： 10.1038/srep09619

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_499

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_500

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Tapered optical fibers are promising one-dimensional nanophotonic waveguides that can provide efficient coupling between their fundamental mode and quantum nanoemitters placed inside them. Here, we present numerical studies on the coupling of single nitrogen-vacancy (NV) centers (single point dipoles) in nanodiamonds with tapered fibers. Our results lead to two important conclusions: (1) A maximum coupling efficiency of 53.4% can be realized for the two fiber ends when the NV bare dipole is located at the center of the tapered fiber. (2) NV centers even in 100-nm-sized nanodiamonds where bulk-like optical properties were reported show a coupling efficiency of 22% at the taper surface, with the coupling efficiency monotonically decreasing as the nanodiamond size increases. These results will be helpful in guiding the development of hybrid quantum devices for applications in quantum information science. (C) 2014 Optical Society of Ameica

DOI： 10.1364/OE.22.020045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Tapered optical fibers are promising one-dimensional nanophotonic waveguides that can provide efficient coupling between their fundamental mode and quantum nanoemitters placed inside them. Here, we present numerical studies on the coupling of single nitrogen-vacancy (NV) centers (single point dipoles) in nanodiamonds with tapered fibers. Our results lead to two important conclusions: (1) A maximum coupling efficiency of 53.4% can be realized for the two fiber ends when the NV bare dipole is located at the center of the tapered fiber. (2) NV centers even in 100-nm-sized nanodiamonds where bulk-like optical properties were reported show a coupling efficiency of 22% at the taper surface, with the coupling efficiency monotonically decreasing as the nanodiamond size increases. These results will be helpful in guiding the development of hybrid quantum devices for applications in quantum information science. (C) 2014 Optical Society of Ameica

DOI： 10.1364/OE.22.020045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Photoluminescence (PL) spectra of single nitrogen vacancy (NV) centers in 50-nm diamond nanocrystals at the zero-phonon line (ZPL) were directly observed using a Fabry-Perot interferometer at cryogenic temperatures. The narrowest linewidth of ZPL was 1.2 GHz (1.9 +/- 0.7 GHz on average), comparable to ZPL linewidths in PL spectra reported for NV centers in pure bulk diamond. This observation is important to the application of NV centers for use in quantum communication and computation devices, and in nano-sensing. (C) 2013 Optical Society of America

DOI： 10.1364/OE.21.029679

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Photoluminescence (PL) spectra of single nitrogen vacancy (NV) centers in 50-nm diamond nanocrystals at the zero-phonon line (ZPL) were directly observed using a Fabry-Perot interferometer at cryogenic temperatures. The narrowest linewidth of ZPL was 1.2 GHz (1.9 +/- 0.7 GHz on average), comparable to ZPL linewidths in PL spectra reported for NV centers in pure bulk diamond. This observation is important to the application of NV centers for use in quantum communication and computation devices, and in nano-sensing. (C) 2013 Optical Society of America

DOI： 10.1364/OE.21.029679

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Crossed structure of a microfluidic channel and an optical channel waveguide is simple and promising to realize detection of weak fluorescence on an integrated device. Usage of TiO2 waveguides is suitable for the device because of the high numerical aperture. In this study, we developed fabrication processes for the TiO2 channel waveguides traversed by microfluidic channels of 0.5-6 mu m widths and investigated the effect of the microfluidic channel to the transmittances. The results elucidated that the photointensity at the microfluidic channel was enough to excite fluorophores. Furthermore, we demonstrated detection of fluorescence from 350 quantum dots. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757759]

DOI： 10.1063/1.4757759

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Crossed structure of a microfluidic channel and an optical channel waveguide is simple and promising to realize detection of weak fluorescence on an integrated device. Usage of TiO2 waveguides is suitable for the device because of the high numerical aperture. In this study, we developed fabrication processes for the TiO2 channel waveguides traversed by microfluidic channels of 0.5-6 mu m widths and investigated the effect of the microfluidic channel to the transmittances. The results elucidated that the photointensity at the microfluidic channel was enough to excite fluorophores. Furthermore, we demonstrated detection of fluorescence from 350 quantum dots. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757759]

DOI： 10.1063/1.4757759

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The temperature dependence of fluorescence spectra of nitrogen vacancy (NV) centers in diamond nanocrystals is investigated in terms of the ability of the substrate to suppress the fluorescence phonon sideband of negatively charged NV (NV-) centers. Three substrates were used: a glass coverslip, undoped silicon (Si), and thermally oxidized silicon (SiO2/Si). Nanocrystals were distributed on these substrates and the temperature dependence of fluorescence spectra of NV- centers of individual nanocrystals were measured in the temperature range 3.5-230 K. We found that the zero-phonon line (ZPL) of NV- centers in nanocrystals on the SiO2/Si substrate remained intense as the temperature was increased from 3.5 to 160 K, whereas it monotonically decreased for the Si substrate. Diamond nanocrystals dispersed on a glass coverslip did not exhibit prominent ZPLs of NV- centers, even at 3.5 K. The temperature dependencies of the peak intensities of NV- centers were quantitatively analyzed by determining the Debye-Waller factors of the three substrates. As the temperature was increased from 3.5 to 230 K, the Debye- Waller factor decreased almost linearly from 10 to 1.7% for the SiO2/Si substrate, decreased from 6.1 to 1.6% for the Si substrate, and decreased from 0.9 to 0.62% for the glass coverslip. These results will be useful for nanophotonic device applications of nanodiamond NV centers in quantum information science and sensing. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.090110

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The temperature dependence of fluorescence spectra of nitrogen vacancy (NV) centers in diamond nanocrystals is investigated in terms of the ability of the substrate to suppress the fluorescence phonon sideband of negatively charged NV (NV-) centers. Three substrates were used: a glass coverslip, undoped silicon (Si), and thermally oxidized silicon (SiO2/Si). Nanocrystals were distributed on these substrates and the temperature dependence of fluorescence spectra of NV- centers of individual nanocrystals were measured in the temperature range 3.5-230 K. We found that the zero-phonon line (ZPL) of NV- centers in nanocrystals on the SiO2/Si substrate remained intense as the temperature was increased from 3.5 to 160 K, whereas it monotonically decreased for the Si substrate. Diamond nanocrystals dispersed on a glass coverslip did not exhibit prominent ZPLs of NV- centers, even at 3.5 K. The temperature dependencies of the peak intensities of NV- centers were quantitatively analyzed by determining the Debye-Waller factors of the three substrates. As the temperature was increased from 3.5 to 230 K, the Debye- Waller factor decreased almost linearly from 10 to 1.7% for the SiO2/Si substrate, decreased from 6.1 to 1.6% for the Si substrate, and decreased from 0.9 to 0.62% for the glass coverslip. These results will be useful for nanophotonic device applications of nanodiamond NV centers in quantum information science and sensing. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.090110

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Language：Japanese   Publishing type：Research paper (other academic)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.019545

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.019545

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Substrates effect is observed on the suppression of the phonon sideband from nitrogen vacancy (NV) centers in 50nm diamond nanocrystals at cryogenic temperatures. As a quantitative parameter of the population of phonon sidebands, the Debye-Waller factor is estimated from fluorescence spectra on glass, silicon, and silica-on-silicon substrates. Fluorescence spectra of negatively charged NV centers in nanodiamonds on silica-on-silicon substrates have average and maximum Debye-Waller factors of 12.7% (which is about six times greater than that of samples on glass substrates) and 19.3%, respectively. This effect is expected to be very important for future applications of NV centers in quantum information science and nanosensing. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.015628

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Substrates effect is observed on the suppression of the phonon sideband from nitrogen vacancy (NV) centers in 50nm diamond nanocrystals at cryogenic temperatures. As a quantitative parameter of the population of phonon sidebands, the Debye-Waller factor is estimated from fluorescence spectra on glass, silicon, and silica-on-silicon substrates. Fluorescence spectra of negatively charged NV centers in nanodiamonds on silica-on-silicon substrates have average and maximum Debye-Waller factors of 12.7% (which is about six times greater than that of samples on glass substrates) and 19.3%, respectively. This effect is expected to be very important for future applications of NV centers in quantum information science and nanosensing. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.015628

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We present a fiber-coupled diamond-based single photon system. Single nanodiamonds containing nitrogen vacancy defect centers are deposited on a tapered fiber of 273 nanometer in diameter providing a record-high number of 689,000 single photons per second from a defect center in a single-mode fiber. The system can be cooled to cryogenic temperatures and coupled evanescently to other nanophotonic structures, such as microresonators. The system is suitable for integrated quantum transmission experiments, two-photon interference, quantum-random-number generation and nano-magnetometry. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.010490

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We present a fiber-coupled diamond-based single photon system. Single nanodiamonds containing nitrogen vacancy defect centers are deposited on a tapered fiber of 273 nanometer in diameter providing a record-high number of 689,000 single photons per second from a defect center in a single-mode fiber. The system can be cooled to cryogenic temperatures and coupled evanescently to other nanophotonic structures, such as microresonators. The system is suitable for integrated quantum transmission experiments, two-photon interference, quantum-random-number generation and nano-magnetometry. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.010490

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Furhter miniaturization of funcionalized quantum optical systems down to nm-dimensions and their integration into fibre optical networks is a major challange for future implementations of quantum information, quantum communication and quantum processing applications. Furthermore, scalability, long-term stability and room-as well as liquid helium temperature operation are benchmarking properties of such systems.
In this paper, we present the realizations of fiber-coupled diamond-based single photon systems. First, an alignment free, mu m-scale single photon source consisting of a single nitrogen vacancy center facet coupled to an optical fiber operating at room temperature is presented. Near-field coupling of the single nitrogen vacancy center is realized by placing a pre-selected nanodiamond directly on the fiber facet in a bottom-up approach. Its photon collection efficiency is comparable to a far-field collection via an air objective with a numerical aperture of 0.82. As the system can be simultaneously excited and its photons be recollected through the fiber, it can be used as a fiber-connected single quantum sensor that allows optical near-field probing on the quantum level. Secondly single nanodiamonds that contain nitrogen vacancy defect centers, are nearfield coupled to a tapered fiber of 300 nanometer in diameter. This system provides a record-high number of 97 kcps single photons from a single defect center into a single mode optical fiber. The entire system can be cooled to liquid Helium temperatures and reheated without breaking. Furhtermore, the system can be evanescently coupled to various nanophotonic structures, e. g. microresonators. The system can also be applied for integrated quantum transmission experiments and the realization of two-photon interference. It can be used as a quantum-random-number generator as well as a probe for nano-magnetometry.

DOI： 10.1117/12.907961

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We report the substrate effects on the zero-phonon transitions and suppression of phonon side bands in the NV center spectrum. Fluorescence spectra of NV centers in cryogenic temperatures were measured by depositing diamond nanocrystals on different substrates including glass slides, undoped Si, and silica (1 similar to 2um) on undoped Si (SiO2/Si). We found that SiO2/Si substrate was an effective substrate to suppress the phonon side band from spectra of NV-centers. Temperature dependence of NV-zero-phonon line Debye-Waller factor on Si and SiO2/Si were measured, from 2.5K to 230K, Debye-Waller factor decreased linearly on both of the two substrates.

DOI： 10.1117/12.906638

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Highly efficient coupling of photons from nanoemitters into single-mode optical fibers is demonstrated using tapered fibers. A percentage (7.4 +/- 1.2%) of the total emitted photons from single CdSe/ZnS nanocrystals were coupled into a 300 nm diameter tapered fiber. The dependence of the coupling efficiency on the taper diameter was investigated and the coupling efficiency was found to increase exponentially with decreasing diameter. This method is very promising for nanoparticle sensing and single-photon sources.

DOI： 10.1021/nl2024867

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

An optical channel waveguide is a key solution to overcome signal propagation delay. For the benefits of miniaturization, development of microfabrication process for waveguides is demanded. TiO2 is one of the suitable candidates for the microfabricated waveguide because of the high refractive index and the transparency. In the present study, conventional microfabrication processes manufactured TiO2 channel waveguides with 1-20 mu m width on oxidized Si substrates and the propagation loss was measured. The prepared channels successfully guided light of 632.8 nm along linear and Y-branched patterns. The propagation loss for the linear waveguide was 9.7 dB/cm. Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3615716]

DOI： 10.1063/1.3615716

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

An optical channel waveguide is a key solution to overcome signal propagation delay. For the benefits of miniaturization, development of microfabrication process for waveguides is demanded. TiO2 is one of the suitable candidates for the microfabricated waveguide because of the high refractive index and the transparency. In the present study, conventional microfabrication processes manufactured TiO2 channel waveguides with 1-20 mu m width on oxidized Si substrates and the propagation loss was measured. The prepared channels successfully guided light of 632.8 nm along linear and Y-branched patterns. The propagation loss for the linear waveguide was 9.7 dB/cm. Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3615716]

DOI： 10.1063/1.3615716

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We investigated the cause of optical transmittance degradation in tapered fibers. Degradation commences immediately after fabrication and it eventually reduces the transmittance to almost zero. It is a major problem that limits applications of tapered fibers. We systematically investigated the effect of the dust-particle density and the humidity on the degradation dynamics. The results clearly show that the degradation is mostly due to dust particles and that it is not related to the humidity. In a dust free environment it is possible to preserve the transmittance with a degradation of less than the noise (+/- 0.02) over 1 week. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.008596

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We investigated the cause of optical transmittance degradation in tapered fibers. Degradation commences immediately after fabrication and it eventually reduces the transmittance to almost zero. It is a major problem that limits applications of tapered fibers. We systematically investigated the effect of the dust-particle density and the humidity on the degradation dynamics. The results clearly show that the degradation is mostly due to dust particles and that it is not related to the humidity. In a dust free environment it is possible to preserve the transmittance with a degradation of less than the noise (+/- 0.02) over 1 week. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.008596

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We succeeded in measuring phase shift spectra of a microsphere cavity coupled with a tapered fiber using a weak coherent probe light at the single photon level. We utilized a tapered fiber with almost no depolarization and constructed a very stable phase shift measurement scheme based on polarization analysis using photon counting. Using a very weak probe light ((n) over bar = 0.41), we succeeded in observing the transition in the phase shift spectrum between undercoupling and overcoupling (at gap distances of 500 and 100 nm, respectively). We also used quantum state tomography to obtain a 'purity spectrum'. Even in the overcoupling regime, the average purity was 0.982 +/- 0.024 (minimum purity: 0.892), suggesting that the coherence of the fiber-microsphere system was well preserved. Based on these results, we believe this system is applicable to quantum phase gates using single light emitters such as diamond nitrogen vacancy centers. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.002278

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We succeeded in measuring phase shift spectra of a microsphere cavity coupled with a tapered fiber using a weak coherent probe light at the single photon level. We utilized a tapered fiber with almost no depolarization and constructed a very stable phase shift measurement scheme based on polarization analysis using photon counting. Using a very weak probe light ((n) over bar = 0.41), we succeeded in observing the transition in the phase shift spectrum between undercoupling and overcoupling (at gap distances of 500 and 100 nm, respectively). We also used quantum state tomography to obtain a 'purity spectrum'. Even in the overcoupling regime, the average purity was 0.982 +/- 0.024 (minimum purity: 0.892), suggesting that the coherence of the fiber-microsphere system was well preserved. Based on these results, we believe this system is applicable to quantum phase gates using single light emitters such as diamond nitrogen vacancy centers. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.002278

DOI： 10.1364/oe.19.002278

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

An ultrahigh-Q optical microcavity coupled with a tapered fiber is an ideal system for the cavity quantum electrodynamics (CQED). In particular realizing this system at cryogenic temperature is vitally important and has been recently explored for various CQED applications including solid-state atom-photon strong coupling, vibrational mode cooling, and photonic quantum gates. These cryogenic fiber-coupled microcavity systems, however, suffer from mechanical vibrations due to cooling systems and distortions caused by large temperature change. These factors may cause the degradation in polarization of probe light field in the system. Here we report the analysis of the polarization state in a tapered-fiber-coupled microsphere cavity at cryogenic temperatures. By scanning the wavelength of the probe light at around 637 nm, which can be used for the diamond nitrogen vacancy centers, the spectral analysis of the polarization state was performed at 8-30 K. We have found that the degree of polarization (DOP, classical analogue of purity) at cryogenic temperatures does not show significant change compared to that measured at room temperature. This fact indicates that the system can conserve the polarization at low temperature to the extent comparable to that at room temperature, which is enough for the evaluation of the quantum phase gate.

DOI： 10.1117/12.874587

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We report our recent experimental demonstration of a KLM CNOT gate[1], a photonic quantum circuit to combine two efficient artificial nonlinear elements. This experimental demonstration[2] confirms the first step in the KLM recipe for all-optical quantum computation, and should be useful for on-demand entanglement generation and purification. We will also report our activities toward the realization of nonlinear sign shift gate using diamond nano-crystals coupled to a microsphere cavity[3]. © 2011 IEEE.

DOI： 10.1109/CLEOE.2011.5943453

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DOI： 10.1143/JJAP.49.119201

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

DOI： 10.1143/JJAP.49.119201

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Language：English   Publisher：JAPAN SOC APPLIED PHYSICS  

DOI： 10.1143/JJAP.49.119201

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Femtosecond one-and two-photon pump-probe dispersive spectroscopic measurements have been applied to the investigation of the vibrational relaxation kinetics of the dark S-1 (2(1)A(g)(-)) state in beta-carotene, combining a higher sensitive detection system with tunable visible and infrared excitation pulses. The two-photon excitation measurements enable the preferential detection of the dark S-1 state. The tunable infrared excitation pulses allowed selective excitation to a different vibrational level of S-1. The S-1 dynamics at early delay times depend strongly on excitation energy. A dependence of the initial S-1 dynamics on excitation energy is discussed in term of the vibrational relaxation of S-1. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.chemphys.2009.12.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

The coupling of a microsphere resonator to a tapered fiber was demonstrated at cryogenic temperatures (8 - 13 K) and investigated with a probe laser light whose frequency around the zero phonon line of nitrogen vacancy centers in diamond (638 nm). For this purpose, a liquid-helium-flow cryostat with a large sample chamber is developed and a resonance dip with a Q of 2 x 10(6) is observed. The resonance frequency and the coupling condition are found to be stable for a period of one hour. (C) 2010 Optical Society of America

DOI： 10.1364/OE.18.015169

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Femtosecond one-and two-photon pump-probe dispersive spectroscopic measurements have been applied to the investigation of the vibrational relaxation kinetics of the dark S-1 (2(1)A(g)(-)) state in beta-carotene, combining a higher sensitive detection system with tunable visible and infrared excitation pulses. The two-photon excitation measurements enable the preferential detection of the dark S-1 state. The tunable infrared excitation pulses allowed selective excitation to a different vibrational level of S-1. The S-1 dynamics at early delay times depend strongly on excitation energy. A dependence of the initial S-1 dynamics on excitation energy is discussed in term of the vibrational relaxation of S-1. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.chemphys.2009.12.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The concurrent dynamics of the electronic excitation and vibronic oscillations of spheroidene have been investigated by means of the transient grating (TG) spectroscopy. The third-order optical responses of spheroidene in an organic solvent, in the LH2 light-harvesting antenna complexes, and in chromatophores have been compared in order to investigate the influence of the environment surrounding this photosynthetic pigment. Vibronic coherent oscillations with a period of several tens of femtosecond have been clearly observed superimposed on a slowly varying background, which reflects the electronic dynamics. The dynamics of the coherent oscillations have been analyzed by means of the wavelet analysis. Within our experimental accuracy, the decay times of the C=C and C-C stretching modes and C-CH(3) rocking mode of each specimen are very close. The experimental results have also been analyzed using a Brownian oscillator model. For these numerical calculations, the spectral density for the underdamped modes has been determined from the Raman spectrum of spheroidene. It was found that the low-frequency modes that reflect the influence of the protein environment can be approximated by the overdamped Brownian oscillator. The experimentally observed linear absorption spectra as well as the third-order optical responses, i.e., TG curves, are reproduced very well by these calculations. The close agreement between the experiments and calculations indicates that the Feynman-diagrammatic approach can be applied to express not only the internal conversion but also the intermolecular excitation energy-transfer processes. The vibronic decay rates of spheroidene in LH2 complexes and chromatophores are evaluated to be about 20% larger than in the organic solvent.

DOI： 10.1103/PhysRevB.81.245112

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The concurrent dynamics of the electronic excitation and vibronic oscillations of spheroidene have been investigated by means of the transient grating (TG) spectroscopy. The third-order optical responses of spheroidene in an organic solvent, in the LH2 light-harvesting antenna complexes, and in chromatophores have been compared in order to investigate the influence of the environment surrounding this photosynthetic pigment. Vibronic coherent oscillations with a period of several tens of femtosecond have been clearly observed superimposed on a slowly varying background, which reflects the electronic dynamics. The dynamics of the coherent oscillations have been analyzed by means of the wavelet analysis. Within our experimental accuracy, the decay times of the C=C and C-C stretching modes and C-CH(3) rocking mode of each specimen are very close. The experimental results have also been analyzed using a Brownian oscillator model. For these numerical calculations, the spectral density for the underdamped modes has been determined from the Raman spectrum of spheroidene. It was found that the low-frequency modes that reflect the influence of the protein environment can be approximated by the overdamped Brownian oscillator. The experimentally observed linear absorption spectra as well as the third-order optical responses, i.e., TG curves, are reproduced very well by these calculations. The close agreement between the experiments and calculations indicates that the Feynman-diagrammatic approach can be applied to express not only the internal conversion but also the intermolecular excitation energy-transfer processes. The vibronic decay rates of spheroidene in LH2 complexes and chromatophores are evaluated to be about 20% larger than in the organic solvent.

DOI： 10.1103/PhysRevB.81.245112

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The vibronic coherence of photosynthetic pigment-protein complexes has been investigated by means of transient grating spectroscopy using sub 20 fs optical pulses. In the present work, we focus our attention on the LH2 antenna complexes from Rhodobacter sphaeroides 2.4.1 because the information about their Structure investigated by the electron and atomic force microscopy is available and the electric levels of pigments are well resolved, resulting in clear absorption spectrum. The vibronic coherent oscillations with a period of a few tens of femtoseconds have been clearly observed We found that the temporal change of the coherent oscillations reflects the vibrational relaxation in the ground state. Calculations based on the Brownian oscillator model were performed Under the impulsive excitation limit. The spectral density has been determined from the Raman measurement of spheroidene. Good agreement between the calculation and the experimental results has been achieved in the linear absorption spectrum and transient grating signal, which strongly Supports the validity of our model. (C) 2009 Elsevier B.V. All rights reserved

DOI： 10.1016/j.jlumin.2009.01.027

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We investigate how structural distortions in carotenoid cause decoherences of its high-frequency vibrational modes by applying the sub-20-fs time-resolved transient grating spectroscopy to beta-catotene and lycopene. The results indicate that the C = C central stretching mode shows significant loss of coherence under the effects of the steric hindrance between beta-ionone ring and polyene backbone, whereas the other high-frequency modes do not show such dependency on the structural distortions. (C) 2000 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2009.04.098

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigate how structural distortions in carotenoid cause decoherences of its high-frequency vibrational modes by applying the sub-20-fs time-resolved transient grating spectroscopy to beta-catotene and lycopene. The results indicate that the C = C central stretching mode shows significant loss of coherence under the effects of the steric hindrance between beta-ionone ring and polyene backbone, whereas the other high-frequency modes do not show such dependency on the structural distortions. (C) 2000 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2009.04.098

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The vibronic coherence of photosynthetic pigment-protein complexes has been investigated by means of transient grating spectroscopy using sub 20 fs optical pulses. In the present work, we focus our attention on the LH2 antenna complexes from Rhodobacter sphaeroides 2.4.1 because the information about their Structure investigated by the electron and atomic force microscopy is available and the electric levels of pigments are well resolved, resulting in clear absorption spectrum. The vibronic coherent oscillations with a period of a few tens of femtoseconds have been clearly observed We found that the temporal change of the coherent oscillations reflects the vibrational relaxation in the ground state. Calculations based on the Brownian oscillator model were performed Under the impulsive excitation limit. The spectral density has been determined from the Raman measurement of spheroidene. Good agreement between the calculation and the experimental results has been achieved in the linear absorption spectrum and transient grating signal, which strongly Supports the validity of our model. (C) 2009 Elsevier B.V. All rights reserved

DOI： 10.1016/j.jlumin.2009.01.027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We present a new method for data acquisition in time-resolved terahertz spectroscopy experiments. Our approach is based on simultaneous collection of reference and differential THz scans. Both the optical THz generation beam and the pump beam are modulated at two different frequencies that are not harmonic with respect to each other. Our method allows not only twice as fast data acquisition but also minimization of noise connected to slowly varying laser power fluctuations and timing instabilities. Our use of the nonlinear crystal N-benzyl-2-methyl-4-nitroaniline (BNA) enables time-resolved THz spectroscopy to beyond 5 THz, thereby highlighting that the presented method is especially valuable at higher frequencies where phase errors in the data acquisition become increasingly important. (C) 2009 Optical Society of America

DOI： 10.1364/OE.17.021969

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We present a new method for data acquisition in time-resolved terahertz spectroscopy experiments. Our approach is based on simultaneous collection of reference and differential THz scans. Both the optical THz generation beam and the pump beam are modulated at two different frequencies that are not harmonic with respect to each other. Our method allows not only twice as fast data acquisition but also minimization of noise connected to slowly varying laser power fluctuations and timing instabilities. Our use of the nonlinear crystal N-benzyl-2-methyl-4-nitroaniline (BNA) enables time-resolved THz spectroscopy to beyond 5 THz, thereby highlighting that the presented method is especially valuable at higher frequencies where phase errors in the data acquisition become increasingly important. (C) 2009 Optical Society of America

DOI： 10.1364/OE.17.021969

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We present a new method for data acquisition in time-resolved terahertz spectroscopy experiments. Our approach is based on simultaneous collection of reference and differential THz scans. Both the optical THz generation beam and the pump beam are modulated at two different frequencies that are not harmonic with respect to each other. Our method allows not only twice as fast data acquisition but also minimization of noise connected to slowly varying laser power fluctuations and timing instabilities. Our use of the nonlinear crystal N-benzyl-2-methyl-4-nitroaniline (BNA) enables time-resolved THz spectroscopy to beyond 5 THz, thereby highlighting that the presented method is especially valuable at higher frequencies where phase errors in the data acquisition become increasingly important. (C) 2009 Optical Society of America

DOI： 10.1364/OE.17.021969

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The ultrafast nonlinear optical responses of all-trans-beta-carotene have been investigated by femtosecond pump-probe spectroscopy under a nonresonant excitation condition to the optically allowed S-2 (1(1)B(u)(+)) state. Instantaneous signals were ascribed to coherent nonlinear optical effects in a three-level electronic system in beta-carotene without any convolution of the population of excited states. The temporal responses of the coherent signals were identified with an instrumental response function of the system. At a longer delay (&gt; 1 ps), transient signals due to the dark S-1 (2(1)A(g)(-)) state induced by two-photon excitation and to the lowest triplet T-1 state induced by four-photon excitation were well temporally and spectrally resolved. The S-1 decay time and T-1 formation time were determined to be 9.5 and 20 ps, respectively. We show the availability of multiphoton excitation spectroscopy for clarifying the ultrafast relaxation kinetics of a complex system.

DOI： 10.1143/JPSJ.78.104715

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The ultrafast nonlinear optical responses of all-trans-beta-carotene have been investigated by femtosecond pump-probe spectroscopy under a nonresonant excitation condition to the optically allowed S-2 (1(1)B(u)(+)) state. Instantaneous signals were ascribed to coherent nonlinear optical effects in a three-level electronic system in beta-carotene without any convolution of the population of excited states. The temporal responses of the coherent signals were identified with an instrumental response function of the system. At a longer delay (&gt; 1 ps), transient signals due to the dark S-1 (2(1)A(g)(-)) state induced by two-photon excitation and to the lowest triplet T-1 state induced by four-photon excitation were well temporally and spectrally resolved. The S-1 decay time and T-1 formation time were determined to be 9.5 and 20 ps, respectively. We show the availability of multiphoton excitation spectroscopy for clarifying the ultrafast relaxation kinetics of a complex system.

DOI： 10.1143/JPSJ.78.104715

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The ultrafast nonlinear optical responses of all-trans-beta-carotene have been investigated by femtosecond pump-probe spectroscopy under a nonresonant excitation condition to the optically allowed S-2 (1(1)B(u)(+)) state. Instantaneous signals were ascribed to coherent nonlinear optical effects in a three-level electronic system in beta-carotene without any convolution of the population of excited states. The temporal responses of the coherent signals were identified with an instrumental response function of the system. At a longer delay (&gt; 1 ps), transient signals due to the dark S-1 (2(1)A(g)(-)) state induced by two-photon excitation and to the lowest triplet T-1 state induced by four-photon excitation were well temporally and spectrally resolved. The S-1 decay time and T-1 formation time were determined to be 9.5 and 20 ps, respectively. We show the availability of multiphoton excitation spectroscopy for clarifying the ultrafast relaxation kinetics of a complex system.

DOI： 10.1143/JPSJ.78.104715

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optical Society of America (OSA)  

An effective and widely tunable means of producing terahertz (THz) radiation using difference-frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated by optimizing the pump wavelengths. We calculated the (wideband) refractive index and coherence length mapping of BNA to establish the optimum phase-matching condition of the DFG configuration. To satisfy the phasematching conditions over the range 0.1-20 THz, both pump wavelengths were varied from 780 to 950 nm, and the optical wavelength dependency of the THz-wave output was clearly observed. We expanded the range of THzwave generation and increased the power output to ten times that obtained using previous methods. ©2009 Optical Society of America.

DOI： 10.1364/OE.17.014832

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

An effective and widely tunable means of producing terahertz (THz) radiation using difference-frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated by optimizing the pump wavelengths. We calculated the (wideband) refractive index and coherence length mapping of BNA to establish the optimum phase-matching condition of the DFG configuration. To satisfy the phase-matching conditions over the range 0.1-20 THz, both pump wavelengths were varied from 780 to 950 nm, and the optical wavelength dependency of the THz-wave output was clearly observed. We expanded the range of THz-wave generation and increased the power output to ten times that obtained using previous methods. (C) 2009 Optical Society of America

DOI： 10.1364/OE.17.014832

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

An effective and widely tunable means of producing terahertz (THz) radiation using difference-frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated by optimizing the pump wavelengths. We calculated the (wideband) refractive index and coherence length mapping of BNA to establish the optimum phase-matching condition of the DFG configuration. To satisfy the phase-matching conditions over the range 0.1-20 THz, both pump wavelengths were varied from 780 to 950 nm, and the optical wavelength dependency of the THz-wave output was clearly observed. We expanded the range of THz-wave generation and increased the power output to ten times that obtained using previous methods. (C) 2009 Optical Society of America

DOI： 10.1364/OE.17.014832

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Transient grating (TG) signals from beta-carotene were measured at various excitation energies (wavelengths). Clear coherent oscillations with a period of a few tens of femtoseconds were observed when the excitation energy was tuned in the vicinity of the absorption edge. It was found that the TG signal is very sensitive to the excitation energy. When the TG signal is measured near the absorption maximum, following the coherent spike at the origin of the time axis, weak coherent oscillations are observed superimposed on a slowly varying background. The rise time of this slowly varying background is 0.4 ps and is followed by the slow decay with a 5 ps time constant. As the excitation energy is decreased the coherent oscillations become more prominent. The coherent oscillations and the slowly varying background become very weak again when the excitation energy is lower than the absorption edge. The TG signals were calculated using two sets of energy and Feynman diagrams to investigate possible pathways of the electronic internal conversion and vibronic decoherence processes. The modeling indicates that the vibronic coherence, initially established by pumping into the excited state S-2, instantaneously decays due to relaxation into an intermediate state S-x, which is located between S-2 and S-1. Possible interpretation of the nature of the S-x state is discussed.

DOI： 10.1103/PhysRevB.80.035118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Transient grating (TG) signals from beta-carotene were measured at various excitation energies (wavelengths). Clear coherent oscillations with a period of a few tens of femtoseconds were observed when the excitation energy was tuned in the vicinity of the absorption edge. It was found that the TG signal is very sensitive to the excitation energy. When the TG signal is measured near the absorption maximum, following the coherent spike at the origin of the time axis, weak coherent oscillations are observed superimposed on a slowly varying background. The rise time of this slowly varying background is 0.4 ps and is followed by the slow decay with a 5 ps time constant. As the excitation energy is decreased the coherent oscillations become more prominent. The coherent oscillations and the slowly varying background become very weak again when the excitation energy is lower than the absorption edge. The TG signals were calculated using two sets of energy and Feynman diagrams to investigate possible pathways of the electronic internal conversion and vibronic decoherence processes. The modeling indicates that the vibronic coherence, initially established by pumping into the excited state S-2, instantaneously decays due to relaxation into an intermediate state S-x, which is located between S-2 and S-1. Possible interpretation of the nature of the S-x state is discussed.

DOI： 10.1103/PhysRevB.80.035118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The ultrafast relaxation kinetics of all-trans-beta-carotene homologs with varying numbers of conjugated double bonds n(n=7-15) and lycopene (n=11) has been investigated using femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies, both carried out under identical excitation conditions. The nonradiative relaxation rates of the optically allowed S-2(1(1)B(u)(+)) state were precisely determined by the time-resolved fluorescence. The kinetics of the optically forbidden S-1(2(1)A(g)(-)) state were observed by the time-resolved absorption measurements. The dependence of the S-1 relaxation rates upon the conjugation length is adequately described by application of the energy gap law. In contrast to this, the nonradiative relaxation rates of S-2 have a minimum at n=9 and show a reverse energy gap law dependence for values of n above 11. This anomalous behavior of the S-2 relaxation rates can be explained by the presence of an intermediate state (here called the S-x state) located between the S-2 and S-1 states at large values of n (such as n=11). The presence of such an intermediate state would then result in the following sequential relaxation pathway S-2 -&gt; S-x -&gt; S-1 -&gt; S-0. A model based on conical intersections between the potential energy curves of these excited singlet states can readily explain the measured relationships between the decay rates and the energy gaps.

DOI： 10.1063/1.3147008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The ultrafast relaxation kinetics of all-trans-beta-carotene homologs with varying numbers of conjugated double bonds n(n=7-15) and lycopene (n=11) has been investigated using femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies, both carried out under identical excitation conditions. The nonradiative relaxation rates of the optically allowed S-2(1(1)B(u)(+)) state were precisely determined by the time-resolved fluorescence. The kinetics of the optically forbidden S-1(2(1)A(g)(-)) state were observed by the time-resolved absorption measurements. The dependence of the S-1 relaxation rates upon the conjugation length is adequately described by application of the energy gap law. In contrast to this, the nonradiative relaxation rates of S-2 have a minimum at n=9 and show a reverse energy gap law dependence for values of n above 11. This anomalous behavior of the S-2 relaxation rates can be explained by the presence of an intermediate state (here called the S-x state) located between the S-2 and S-1 states at large values of n (such as n=11). The presence of such an intermediate state would then result in the following sequential relaxation pathway S-2 -&gt; S-x -&gt; S-1 -&gt; S-0. A model based on conical intersections between the potential energy curves of these excited singlet states can readily explain the measured relationships between the decay rates and the energy gaps.

DOI： 10.1063/1.3147008

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

We investigate transient grating signals in beta-carotene homologues by using sub-20-fs optical pulses. The results clearly show that shorter-chain carotenoids have a specific major channel of energy dissipation to the environment (the central C=C stretching mode) in the ground-state vibrational manifold, whereas the longer-chain carotenoids do not.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

We investigate the third-order nonlinear optical property of a range of beta-carotene homologues, which have different numbers (n) of conjugated C=C double bonds from n = 7 to 15, by using third-harmonic generation Maker fringe technique. The results clearly show that there is a remarkable enhancement of the third-order optical nonlinearity when n = 15, which is a four fold increase compared with n = 11 (i.e. beta-carotene). (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.200881296

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

The vibronic coherence of beta-carotene in benzene has been investigated by means of transient grating spectroscopy using sub 20-fs optical pulses. The coherent oscillations with a period of a few tens of femtoseconds have been clearly observed, which reflect the C-C and C=C stretching modes and the C-CH3 rocking mode of the polyene backbone. We found that the signal is very sensitive to the excitation wavelength. Calculations based on a Brownian oscillator model were performed. We show that the experimental results are well explained by properly considering the excitation pulse shapes. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.200881344

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

Ultrafast degenerate four-wave mixing (DFWM) signals of the regioregular (RR) poly(3-hexylthiophene) (P3HT) film have been investigated by the experiments using sub-20 fs pulses generated from a noncollinear optical parametric amplifier (NOPA) system. Strong DFWM signals were observed owing to a large third-order nonlinear susceptibility. chi((3)) of the RR-P3HT film. The time profile of the DFWM signals exhibits clear coherent oscillation on a decaying signal. The oscillation turn out to be caused by the C=C stretching mode that gives strong Raman signal. The time profile of the DFWM signal is simulated by a numerical calculation. The result of simulation reveals that decay constants of electronic population and of vibronic oscillation are 200 fs and 210 fs, respectively. This is the first determination of the decay constants for the RR-P3HT film. The obtained result demonstrates that the. chi((3)) signal of the RR-P3HT film decays very rapidly. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.200881304

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We show that a very large enhancement of third-order optical nonlinearity (gamma) of pi-conjugated molecules can be realized without a major redshift of the absorption spectrum that disturbs optical transparency in the visible region. By changing the number (n) of C=C bonds of beta carotene (n=11) from 7 to 15, a remarkable 3.4-fold increase in the gamma value was observed when n=15 relative to that of beta carotene. This enhancement of gamma mainly originates from three-photon resonance of a lowest optically allowed excited state. The controversial higher-lying essential state is not important for generating the large value of gamma.

DOI： 10.1103/PhysRevB.78.161101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We show that a very large enhancement of third-order optical nonlinearity (gamma) of pi-conjugated molecules can be realized without a major redshift of the absorption spectrum that disturbs optical transparency in the visible region. By changing the number (n) of C=C bonds of beta carotene (n=11) from 7 to 15, a remarkable 3.4-fold increase in the gamma value was observed when n=15 relative to that of beta carotene. This enhancement of gamma mainly originates from three-photon resonance of a lowest optically allowed excited state. The controversial higher-lying essential state is not important for generating the large value of gamma.

DOI： 10.1103/PhysRevB.78.161101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Transient grating (TG) signals in 8-carotene homologues, by using sub-20-fs excitation pulses, were measured in order to investigate the dependence of the vibrational coherence dynamics on the pi-conjugation length of these carotenoids. The experimental TG traces can be well reproduced by computational simulations based on a Brownian oscillator model using the spectral density determined from their respective resonance Raman spectra and their previously reported excited-state population-relaxation times. The total dephasing times of the ground-state vibrational modes of the homologues were determined by applying a wavelet transformation of their coherent oscillations, which were observed in the experimental TG traces. The total dephasing time decreases as the number of conjugated C=C double bonds increases. The decoherence of the ground-state vibrational modes in the homologues is mainly caused by system-bath interactions. The dephasing time of the C-C stretching modes strongly depends on the conjugation length, whereas that of the C=C stretching does not. This trend clearly shows that shorter-chain carotenoids have a specific major channel of energy dissipation to the environment (the C=C stretching), whereas the longer-chain carotenoids do not.

DOI： 10.1103/PhysRevB.77.205118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Transient grating (TG) signals in 8-carotene homologues, by using sub-20-fs excitation pulses, were measured in order to investigate the dependence of the vibrational coherence dynamics on the pi-conjugation length of these carotenoids. The experimental TG traces can be well reproduced by computational simulations based on a Brownian oscillator model using the spectral density determined from their respective resonance Raman spectra and their previously reported excited-state population-relaxation times. The total dephasing times of the ground-state vibrational modes of the homologues were determined by applying a wavelet transformation of their coherent oscillations, which were observed in the experimental TG traces. The total dephasing time decreases as the number of conjugated C=C double bonds increases. The decoherence of the ground-state vibrational modes in the homologues is mainly caused by system-bath interactions. The dephasing time of the C-C stretching modes strongly depends on the conjugation length, whereas that of the C=C stretching does not. This trend clearly shows that shorter-chain carotenoids have a specific major channel of energy dissipation to the environment (the C=C stretching), whereas the longer-chain carotenoids do not.

DOI： 10.1103/PhysRevB.77.205118

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Widely tunable terahertz (THz)-wave generation using difference frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. To our knowledge, this is the first report of THz-wave generation by BNA DFG. Large, high-quality single crystals of BNA (φ 8 mm × 30 mm) were grown using the vertical Bridgman method. The nonlinear optical (NLO) coefficient d33 of the BNA crystal is ∼234 pm/V, which is the largest value reported for any yellow NLO material. The collinear phase-matching condition of the type-0 configuration is satisfied using a 0.7-1 μm band pump wavelength. We generated THz waves using an organic BNA crystal
the generation range is 0.1-15 THz. © 2008 Optical Society of America.

DOI： 10.1364/OL.33.000252

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The third-order nonlinear optical responses of beta-carotene and its homologue having a conjugation-double bond n = 15 have been investigated using sub-20 fs ultra-short optical pulses in order to clarify the dissipation processes of excess energy. Using the four-wave mixing spectroscopy, we observed a clear coherent oscillation with a period of a few tens of femtoseconds. The spectral density of these molecules was estimated that allowed the theoretical linear and nonlinear optical signals to be directly compared with the experimental data. Calculations based on the Brownian oscillator model were performed under the impulsive excitation limit. We show that the memory of the vibronic coherence generated upon the excitation into the S-2 state is lost via the relaxation process including the S-1 state. The vibronic decoherence lifetime of the system was estimated to be 1 ps, which is about 5 times larger than the life time of the S-2 state (similar to 150 fs) determined in previous studies. The role of coherence and the efficient energy transfer in the light-harvesting antenna complexes are discussed.

DOI： 10.1007/s11120-007-9265-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Widely tunable terahertz (THz)-wave generation using difference frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. To our knowledge, this is the first report of THz-wave generation by BNA DFG. Large, high-quality single crystals of BNA (0 8 mm X 30 mm) were grown using the vertical Bridgman method. The nonlinear optical (NLO) coefficient d(33) of the BNA crystal is similar to 234 pm/V, which is the largest value reported for any yellow NLO material. The collinear phase-matching condition of the type-0 configuration is satisfied using a 0.7-1 mu m band pump wavelength. We generated THz waves using an organic BNA crystal; the generation range is 0.1-15 THz. (C) 2008 Optical Society of America.

DOI： 10.1364/OL.33.000252

DOI： 10.1364/ol.33.000252

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The third-order nonlinear optical responses of beta-carotene and its homologue having a conjugation-double bond n = 15 have been investigated using sub-20 fs ultra-short optical pulses in order to clarify the dissipation processes of excess energy. Using the four-wave mixing spectroscopy, we observed a clear coherent oscillation with a period of a few tens of femtoseconds. The spectral density of these molecules was estimated that allowed the theoretical linear and nonlinear optical signals to be directly compared with the experimental data. Calculations based on the Brownian oscillator model were performed under the impulsive excitation limit. We show that the memory of the vibronic coherence generated upon the excitation into the S-2 state is lost via the relaxation process including the S-1 state. The vibronic decoherence lifetime of the system was estimated to be 1 ps, which is about 5 times larger than the life time of the S-2 state (similar to 150 fs) determined in previous studies. The role of coherence and the efficient energy transfer in the light-harvesting antenna complexes are discussed.

DOI： 10.1007/s11120-007-9265-y

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Widely tunable terahertz (THz) -wave generation using difference frequency generation (DFG) in an organic N-Benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. An organic nonlinear optical (NLO) BNA crystal is one of the promising materials for efficient and strong THz-wave generation because of its potential to have a sufficiently large enough second-order optical nonlinearity. Large and high quality single crystals of BNA (phi 8x30mm) were successfully grown by a vertical Bridgman method. The NLO coefficient d(33) of BNA crystal is about 230pm/V. It is the largest value reported for any yellow-colored NLO materials. BNA has low refractive index dispersion between the optical and THz-wave region, therefore the colinear phase matching condition of the Type0 configuration is satisfied by using 0.7 similar to 1 mu m band pump wavelength. So, we developed a near-infrared dual-wavelength pump source for BNA-DFG. Two KTiOPO4 (KTP) crystals were mounted on galvano scanners inside a double-pass optical parametric oscillator (OPO). It is pumped using a frequency-doubled Nd:YAG laser (532 nm, 8 ns, 100 Hz). The signal wave of the KTP-OPO output was controlled independently and rapidly using a galvano scanner. We successfully generated THz-wave using organic BNA crystal. The THz-wave generation range is from 0.1 to 15THz, while the pumping dual-wavelength is controlled in the 0.8-0.9 mu m range.

DOI： 10.1117/12.762620

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Linear and second-order nonlinear optical (NLO) properties of a single crystal of N-benzyl-2-methyl-4-nitroaniline (BNA) have been determined. The refractive indices of the crystal were measured in the visible to near infra-red region. The Maker-fringe and phase-matching methods were used to determine the magnitudes of the d-tensor components for the second harmonic generation when excited the crystals at 1064 nm. They were d(333) = 234 +/- 31, d(322) = 15.6 +/- 0.9, and d(311) similar to 0 pm/V. The value of d(333) is the largest value reported for any yellow-colored NLO materials and suggests that crystals of BNA will be very effective for terahertz wave generation.

DOI： 10.1143/JJAP.46.1528

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

A single crystal of N-benzyl 2-methyl-4-nitroaniline (BNA) whose dimensions were 8 x 10 mm (diameter x length) was grown using a vertical Bridgman method with sufficient optical transparency for spectroscopic use. Polarized reflection spectra of the crystal were measured in order to determine its linear optical parameters (refractive indices and extinction coefficients). The relative magnitudes of the d-tensor components of the crystal were determined to be d(333) = (17 +/- 9) x d(322,) d(322) &gt; d(311), d(311) similar to 0 from polarization dependencies of the second harmonic generation. These results are in disagreement with previously reported theoretical studies, in which the effects of intermolecular interactions were completely neglected. Here, we have included these intermolecular interactions in the calculations assuming the presence of supra-molecular clusters. We conclude that the anomalous enhancement of d(333) is due to the interactions along the direction of the hydrogen bonds in the crystal and the resonance effect.

DOI： 10.1143/JJAP.45.8676

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

A single crystal of N-benzyl 2-methyl-4-nitroaniline (BNA) whose dimensions were 8 x 10 mm (diameter x length) was grown using a vertical Bridgman method with sufficient optical transparency for spectroscopic use. Polarized reflection spectra of the crystal were measured in order to determine its linear optical parameters (refractive indices and extinction coefficients). The relative magnitudes of the d-tensor components of the crystal were determined to be d(333) = (17 +/- 9) x d(322,) d(322) &gt; d(311), d(311) similar to 0 from polarization dependencies of the second harmonic generation. These results are in disagreement with previously reported theoretical studies, in which the effects of intermolecular interactions were completely neglected. Here, we have included these intermolecular interactions in the calculations assuming the presence of supra-molecular clusters. We conclude that the anomalous enhancement of d(333) is due to the interactions along the direction of the hydrogen bonds in the crystal and the resonance effect.

DOI： 10.1143/JJAP.45.8676

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

We have measured the refractive index and absorption coefficient of the N-benzyl-2-methyl-4-nitroaniline crystal using terahertz time-domain spectroscopy. We found that the refractive index had a value between 1.5 and 1.9 in the (100) direction and between 1.9 and 2.3 in the (100) direction. We also found that there were resonances at 1.6 and 3.2 THz in the (100) direction, and 1.3, 2.2, and 3.6 THz in the (001) direction within the observed spectral range between 0 and 5 THz. A Lorentz-type oscillator model is applicable to explain our experimental observations.

DOI： 10.1143/JJAO.45.L761

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We studied terahertz (THz) electromagnetic wave emission and detection using highly purified N-benzyl-2-methyl-4-nitroaniline (BNA) crystals. In THz emission experiments, we compared the efficiencies of THz emission via optical rectification for BNA, ZnTe, and GaP crystals, and confirmed that the BNA crystal is the most efficient THz emitter among these three crystals within the frequency range limits for observation. In the THz detection experiment, we also compared the modulation efficiencies of the BNA and ZnTe crystals, and found that the ZnTe crystal has a higher efficiency than the BNA crystal. However, the BNA crystal has a higher efficiency than the ZnTe crystal in high-frequency regions. Since the BNA crystal is suitable for detecting a high-frequency region even when using thick crystals, it is expected that the BNA crystal as a THz detector will be easy to prepare and handle.

DOI： 10.1143/JJAP.45.4068

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We introduce nanofiber Bragg cavities fulfilling three important requirements: small mode-volume, wide tuning-range, and efficient fiber-coupling. In a first application, we show enhancement of single quantum emitters such as quantum dots and nitrogen vacancy centers. (C) 2014 Optical Society of America

DOI： 10.1364/CLEO_AT.2015.JTu5A.83

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We introduce nanofiber Bragg cavities fulfilling three important requirements: small mode-volume, wide tuning-range, and efficient fiber-coupling. In a first application, we show enhancement of single quantum emitters such as quantum dots and nitrogen vacancy centers. (C) 2014 Optical Society of America

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：IEEE  

We introduce nanofiber Bragg cavities fulfilling three important requirements: small mode-volume, wide tuning-range, and efficient fiber-coupling. In a first application, we show enhancement of single quantum emitters such as quantum dots and nitrogen vacancy centers. (C) 2014 Optical Society of America

DOI： 10.1364/CLEO_AT.2015.JTu5A.83

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Language：English   Publisher：IEEE  

We introduce nanofiber Bragg cavities fulfilling three important requirements: small mode-volume, wide tuning-range, and efficient fiber-coupling. In a first application, we show enhancement of single quantum emitters such as quantum dots and nitrogen vacancy centers. (C) 2014 Optical Society of America

DOI： 10.1364/CLEO_AT.2015.JTu5A.83

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We introduce nanofiber Bragg cavities fulfilling three important requirements: small mode-volume, wide tuning-range, and efficient fiber-coupling. In a first application, we show enhancement of single quantum emitters such as quantum dots and nitrogen vacancy centers. (C) 2014 Optical Society of America

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We introduce nanofiber Bragg cavities fulfilling three important requirements: small mode-volume, wide tuning-range, and efficient fiber-coupling. In a first application, we show enhancement of single quantum emitters such as quantum dots and nitrogen vacancy centers. (C) 2014 Optical Society of America

DOI： 10.1364/CLEO_AT.2015.JTu5A.83

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Nitrogen vacancy (NV) centers in nanodiamonds can be efficiently fiber coupled with tapered fibers. We report 689kHz single photon NV emission into single-mode fibers at 293K and first cryogenic experiments towards indistinguishable single photon generation. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600126

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Nitrogen vacancy (NV) centers in nanodiamonds can be efficiently fiber coupled with tapered fibers. We report 689kHz single photon NV emission into single-mode fibers at 293K and first cryogenic experiments towards indistinguishable single photon generation. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600126

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We report efficient coupling of nanoemitters and single-mode fibers. 7.4% of the total emitted photons from single CdSe/ZnS nanocrystals were directly coupled into 300-nm-diameter tapered fibers and were output from the single-mode fiber ends.

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We report efficient coupling of nanoemitters and single-mode fibers. 7.4% of the total emitted photons from single CdSe/ZnS nanocrystals were directly coupled into 300-nm-diameter tapered fibers and were output from the single-mode fiber ends.

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Article

CiNii Books

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Language：Japanese  

J-GLOBAL

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Article

CiNii Books

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Language：Japanese  

CiNii Article

CiNii Books

J-GLOBAL

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Article

CiNii Books

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：上智大学四谷キャンパス  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：上智大学四谷キャンパス  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Nara Kasugano International Forum  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪府立大学中百舌鳥キャンパス サイエンスホール（A12棟）  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Awaji-Island, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Oral presentation (general)  

Venue：大阪市立大学  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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