研究者詳細 - 藤原　正澄

論文 - 藤原　正澄

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Bright Quantum-Grade Fluorescent Nanodiamonds

Keisuke Oshimi, Hitoshi Ishiwata, Hiromu Nakashima, Sara Mandić, Hina Kobayashi, Minori Teramoto, Hirokazu Tsuji, Yoshiki Nishibayashi, Yutaka Shikano, Toshu An, Masazumi Fujiwara

ACS Nano 2024年12月

Size, polyglycerol grafting, and net surface charge of iron oxide nanoparticles determine their interaction and toxicity in Caenorhabditis elegans. 査読国際誌

Yajuan Zou, Yutaka Shikano, Yuta Nishina, Naoki Komatsu, Eriko Kage-Nakadai, Masazumi Fujiwara

Chemosphere 142060 - 142060 2024年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

The widespread application of engineered nanoparticles (NPs) in environmental remediation has raised public concerns about their toxicity to aquatic organisms. Although appropriate surface modification can mitigate the ecotoxicity of NPs, the lack of polymer coating to inhibit toxicity completely and the insufficient knowledge about charge effect hinder the development of safe nanomaterials. Herein, we explored the potential of polyglycerol (PG) functionalization in alleviating the environmental risks of NPs. Iron oxide NPs (ION) of 20, 100, and 200 nm sizes (IONS, IONM and IONL, respectively) were grafted with PG to afford ION-PG. We examined the interaction of ION and ION-PG with Caenorhabditis elegans (C. elegans) and found that PG suppressed non-specific interaction of ION with C. elegans to reduce their accumulation and to inhibit their translocation. Particularly, IONS-PG was completely excluded from worms of all developmental stages. By covalently introducing sulfate, carboxyl and amino groups onto IONS-PG, we further demonstrated that positively charged IONS-PG-NH3+ induced high intestinal accumulation, cuticle adhesion and distal translocation, whereas the negatively charged IONS-PG-OSO3- and IONS-PG-COO- were excreted out. Consequently, no apparent deleterious effects on brood size and life span were observed in worms treated by IONS-PG and IONS-PG bearing negatively charged groups. This study presents new surface functionalization approaches for developing ecofriendly nanomaterials.

DOI： 10.1016/j.chemosphere.2024.142060

Diamond quantum sensors in microfluidics technology 査読

17 ( 5 ) 2023年9月

Glass-patternable notch-shaped microwave architecture for on-chip spin detection in biological samples. 査読国際誌

Keisuke Oshimi, Yushi Nishimura, Tsutomu Matsubara, Masuaki Tanaka, Eiji Shikoh, Li Zhao, Yajuan Zou, Naoki Komatsu, Yuta Ikado, Yuka Takezawa, Eriko Kage-Nakadai, Yumi Izutsu, Katsutoshi Yoshizato, Saho Morita, Masato Tokunaga, Hiroshi Yukawa, Yoshinobu Baba, Yoshio Teki, Masazumi Fujiwara

Lab on a chip 22 ( 13 ) 2519 - 2530 2022年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We report a notch-shaped coplanar microwave waveguide antenna on a glass plate designed for on-chip detection of optically detected magnetic resonance (ODMR) of fluorescent nanodiamonds (NDs). A lithographically patterned thin wire at the center of the notch area in the coplanar waveguide realizes a millimeter-scale ODMR detection area (1.5 × 2.0 mm2) and gigahertz-broadband characteristics with low reflection (∼8%). The ODMR signal intensity in the detection area is quantitatively predictable by numerical simulation. Using this chip device, we demonstrate a uniform ODMR signal intensity over the detection area for cells, tissue, and worms. The present demonstration of a chip-based microwave architecture will enable scalable chip integration of ODMR-based quantum sensing technology into various bioassay platforms.

DOI： 10.1039/d2lc00112h

Probing the Role of Charged Functional Groups on Nanoparticles Grafted with Polyglycerol in Protein Adsorption and Cellular Uptake 査読

Yajuan Zou, Shinji Ito, Masazumi Fujiwara, Naoki Komatsu

ADVANCED FUNCTIONAL MATERIALS 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-V C H VERLAG GMBH

In biofluids, charged functional groups on the surface of nanoparticles (NPs) interact with cells through the protein corona. However, the cascade effects of charged groups on corona formation and cellular uptake remain unclear. Herein, carboxy, sulfate, and amino groups are quantitatively introduced at the periphery of polyglycerol (PG)-grafted nanodiamond and superparamagnetic iron oxide NP to probe their roles in corona formation and cellular uptake. The uptake efficiency and intracellular aggregation state of NPs are revealed to correlate with protein affinity of the charged groups; sulfate at lower density and carboxylate exhibit no affinity to proteins, inducing negligible or no cellular uptake. In contrast, sulfate at higher density and ammonium associate with fetal bovine serum proteins to alter the aggregation state of the internalized NPs. It is further demonstrated that the distinct protein corona profiles on NP-PG-OSO3- and NP-PG-NH3+ surfaces dictate their uptake mechanism. The protein corona of NP-PG-OSO3- suppresses cellular uptake via downregulation of macropinocytosis and clathrin-mediated endocytosis, whereas that of NP-PG-NH3+ enhances uptake through upregulation of macropinocytosis and caveolae-mediated endocytosis. This study clarifies the elusive role of the charged groups in protein adsorption and cellular uptake, which sheds light on NP design for controlled cellular uptake and theranostics in nanomedicine.

DOI： 10.1002/adfm.202111077

π-Topology and ultrafast excited-state dynamics of remarkably photochemically stabilized pentacene derivatives with radical substituents 査読

Nishiki Minami, Kohei Yoshida, Keijiro Maeguchi, Ken Kato, Akihiro Shimizu, Genta Kashima, Masazumi Fujiwara, Chiasa Uragami, Hideki Hashimoto, Yoshio Teki

Physical Chemistry Chemical Physics 24 ( 22 ) 13514 - 13518 2022年

掲載種別：研究論文（学術雑誌）出版者・発行元：Royal Society of Chemistry (RSC)

π-Topologically different pentacene derivatives (1m and 1p) exhibited remarkable photochemical stability owing to the ultrafast ICS induced by a π-radical substituent. The relationship between the π-topology and the photostability is discussed.

DOI： 10.1039/d2cp00683a

Diamond quantum thermometry: from foundations to applications 招待査読

Nanotechnology 32 ( 48 ) 482002 - 482002 2021年11月

Wide-field fluorescent nanodiamond spin measurements toward real-time large-area intracellular thermometry. 国際誌

Yushi Nishimura, Keisuke Oshimi, Yumi Umehara, Yuka Kumon, Kazu Miyaji, Hiroshi Yukawa, Yutaka Shikano, Tsutomu Matsubara, Masazumi Fujiwara, Yoshinobu Baba, Yoshio Teki

Scientific reports 11 ( 1 ) 4248 - 4248 2021年2月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Measuring optically detected magnetic resonance (ODMR) of diamond nitrogen vacancy centers significantly depends on the photon detectors used. We study camera-based wide-field ODMR measurements to examine the performance in thermometry by comparing the results to those of the confocal-based ODMR detection. We show that the temperature sensitivity of the camera-based measurements can be as high as that of the confocal detection and that possible artifacts of the ODMR shift are produced owing to the complexity of the camera-based measurements. Although measurements from wide-field ODMR of nanodiamonds in living cells can provide temperature precisions consistent with those of confocal detection, the technique requires the integration of rapid ODMR measurement protocols for better precisions. Our results can aid the development of camera-based real-time large-area spin-based thermometry of living cells.

DOI： 10.1038/s41598-021-83285-y

Real-time estimation of the optically detected magnetic resonance shift in diamond quantum thermometry toward biological applications 査読

Fujiwara Masazumi, Dohms Alexander, Suto Ken, Nishimura Yushi, Oshimi Keisuke, Teki Yoshio, Cai Kai, Benson Oliver, Shikano Yutaka

PHYSICAL REVIEW RESEARCH 2 ( 4 ) 043415 2020年12月

Real-time nanodiamond thermometry probing in vivo thermogenic responses 査読国際誌

Fujiwara Masazumi, Sun Simo, Dohms Alexander, Nishimura Yushi, Suto Ken, Takezawa Yuka, Oshimi Keisuke, Zhao Li, Sadzak Nikola, Umehara Yumi, Teki Yoshio, Komatsu Naoki, Benson Oliver, Shikano Yutaka, Kage-Nakadai Eriko

SCIENCE ADVANCES 6 ( 37 ) eaba9636 2020年9月

Photoprotective mechanisms in the core LH1 antenna pigment-protein complex from the purple photosynthetic bacterium, Rhodospirillum rubrum 査読

Uragami Chiasa, Sato Hiroki, Yukihira Nao, Fujiwara Masazumi, Kosumi Daisuke, Gardiner Alastair T, Cogdell Richard J, Hashimoto Hideki

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 400 112628 2020年9月

蛍光ナノダイヤモンドによる幹細胞再生機能温度センシング

宮地冬, 小林香央里, 西村勇姿, 藤原正澄, 湯川博, 馬場嘉信

Organ Biology 27 ( 2 ) 185 - 190 2020年7月

記述言語：日本語出版者・発行元：(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。

Operando time-resolved diffuse reflection spectroscopy: The origins of photocatalytic water-oxidation activity of bismuth vanadate

Ryo Miyasato, Masazumi Fujiwara, Chiasa Uragami, Haruyuki Sato, Toshihiro Yano, Hideki Hashimoto

Journal of Photochemistry and Photobiology A: Chemistry 395 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier B.V.

Photocatalytic water splitting has been believed to be a key technology for the construction of a sustainable society based on a renewable energy source. Understanding the exact mechanisms of oxygen evolution by water-splitting reaction, which has been regarded as a bottleneck to realize the water splitting in practical basis, should help us to enhance solar-to-hydrogen energy conversion efficiency. Here, we present a detailed investigation based on two types of bismuth vanadate (BiVO4) crystals. One is a monoclinic scheelite crystal that forms a truncated tetragonal bipyramidal shape (MS), and the other is a tetragonal zircon crystal that forms an octahedral shape (TZ). MS, which has relatively higher photocatalytic activity of water oxidation, rarely adsorbed reduced mediator (Fe2+). Operando time-resolved diffuse reflection spectral measurement demonstrated, for the first time, that the surface holes of MS crystals show extremely high reactivity, while those of TZ crystals show poor reactivity. Our investigation would promote an essential understanding of the photocatalytic reaction mechanism of water oxidation.

DOI： 10.1016/j.jphotochem.2020.112493

A quantum thermometric sensing and analysis system using fluorescent nanodiamonds for the evaluation of living stem cell functions according to intracellular temperature 査読

Yukawa Hiroshi, Fujiwara Masazumi, Kobayashi Kaori, Kumon Yuka, Miyaji Fuyu, Nishimura Yushi, Oshimi Keisuke, Umehara Yumi, Teki Yoshio, Iwasaki Takayuki, Hatano Mutsuko, Hashimoto Hideki, Baba Yoshinobu

NANOSCALE ADVANCES 2 ( 5 ) 1859 - 1868 2020年5月

蛍光ナノダイヤモンドによる幹細胞再生機能温度センシング査読

宮地冬, 小林香央里, 西村勇姿, 藤原正澄, 湯川博, 馬場嘉信

一般社団法人日本臓器保存生物医学会 Organ Biology 27 ( 2 ) 185 - 190 2020年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：(一社)日本臓器保存生物医学会

<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

Removing Non-Size-Dependent Electron Spin Decoherence of Nanodiamond Quantum Sensors by Aerobic Oxidation 査読

Tsukahara Ryuta, Fujiwara Masazumi, Sera Yoshihiko, Nishimura Yushi, Sugai Yuko, Jentgens Christian, Teki Yoshio, Hashimoto Hideki, Shikata Shinichi

ACS APPLIED NANO MATERIALS 2 ( 6 ) 3701 - 3710 2019年6月

Particle size effects of tetrahedron-shaped Ag3PO4 photocatalyst on water-oxidation activity and carrier recombination dynamics 査読

RyoMiyasato, MasazumiFujiwara, HaruyukiSato, ToshihiroYano, HidekiHashimoto

Chemical Physics Letters: X 2 100023 2019年4月

Monitoring spin coherence of single nitrogen-vacancy centers in nanodiamonds during pH changes in aqueous buffer solutions 査読

Masazumi Fujiwara, Ryuta Tsukahara, Yoshihiko Sera, Hiroshi Yukawa, Yoshinobu Baba, Shinichi Shikata, Hideki Hashimoto

RSC Advances 9 ( 22 ) 12606 - 12614 2019年

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 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

Correlation between surface carrier dynamics and water oxidation activity of commercially available rutile-type TiO2 powders 査読

Miyasato Ryo, Fujiwara Masazumi, Sato Haruyuki, Yano Toshihiro, Hashimoto Hideki

CHEMICAL PHYSICS LETTERS 712 123 - 127 2018年11月

Observation of the linewidth broadening of single spins in diamond nanoparticles in aqueous fluid and its relation to the rotational Brownian motion 査読

Fujiwara Masazumi, Shikano Yutaka, Tsukahara Ryuta, Shikata Shinichi, Hashimoto Hideki

SCIENTIFIC REPORTS 8 14773 2018年10月

Surface and bulk carrier recombination dynamics of rutile type TiO2 powder as revealed by sub-ns time-resolved diffuse reflection spectroscopy 査読

Ryo Miyasato, Haruyuki Sato, Toshihiro Yano, Masazumi Fujiwara, Hideki Hashimoto

Journal of Photochemistry and Photobiology A: Chemistry 358 452 - 458 2018年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Strategies to enhance the excitation energy-transfer efficiency in a light-harvesting system using the intramolecular charge transfer character of carotenoids 査読

Nao Yukihira, Yuko Sugai, Masazumi Fujiwara, Daisuke Kosumi, Masahiko Iha, Kazuhiko Sakaguchi, Shigeo Katsumura, Alastair T. Gardiner, Richard J. Cogdell, Hideki Hashimoto

FARADAY DISCUSSIONS 198 59 - 71 2017年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Fiber-Coupled Diamond Micro-Waveguides toward an Efficient Quantum Interface for Spin Defect Centers 査読

Masazumi Fujiwara, Oliver Neitzke, Tim Schröder, Andreas W. Schell, Janik Wolters, Jiabao Zheng, Sara Mouradian, Mohamed Almoktar, Shigeki Takeuchi, Dirk Englund, Oliver Benson

ACS Omega 2 ( 10 ) 7194 - 7202 2017年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Manipulation of single nanodiamonds to ultrathin fiber-taper nanofibers and control of NV-spin states toward fiber-integrated λ-systems. 査読

Fujiwara M, Yoshida K, Noda T, Takashima H, Schell AW, Mizuochi N, Takeuchi S

Nanotechnology 27 ( 45 ) 455202 2016年11月

Detailed numerical analysis of photon emission from a single light emitter coupled with a nanofiber Bragg cavity 査読

Hideaki Takashima, Masazumi Fujiwara, Andreas W. Schell, Shigeki Takeuchi

OPTICS EXPRESS 24 ( 13 ) 15050 - 15058 2016年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optical tracking of picosecond coherent phonon pulse focusing inside a sub-micron object 査読

Thomas Dehoux, Kenichi Ishikawa, Paul H Otsuka, Motonobu Tomoda, Osamu Matsuda, Masazumi Fujiwara, Shigeki Takeuchi, Istvan A Veres, Vitalyi E Gusev, Oliver B Wright

Light: Science and Applications 5 ( 5 ) e16082 2016年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optical tracking of picosecond coherent phonon pulse focusing inside a sub-micron object 査読

Thomas Dehoux, Kenichi Ishikawa, Paul H. Otsuka, Motonobu Tomoda, Osamu Matsuda, Masazumi Fujiwara, Shigeki Takeuchi, Istvan A. Veres, Vitalyi E. Gusev, Oliver B. Wright

LIGHT-SCIENCE & APPLICATIONS 5 2016年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Measuring the charge density of a tapered optical fiber using trapped microparticles 査読

Kazuhiko Kamitani, Takuya Muranaka, Hideaki Takashima, Masazumi Fujiwara, Utako Tanaka, Shigeki Takeuchi, Shinji Urabe

OPTICS EXPRESS 24 ( 5 ) 4672 - 4679 2016年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Ultra-widely tunable nanofiber Bragg cavities for quantum optics 査読

Andreas W. Schell, Hideaki Takashima, Shunya Kamioka, Yasuko Oe, Shinjiro Fujita, Masazumi Fujiwara, Oliver Benson, Shigeki Takeuchi

2015 11th Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2015 3 2016年1月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

Numerical simulation of an ultra-wide tunability and enhanced spontaneous emission of a nanofiber Bragg cavity 査読

Hideaki Takashima, Andreas W. Schell, Shinjiro Fujita, Yasuko Oe, Syunya Kamioka, Masazumi Fujiwara, Shigeki Takeuchi

2015 11th Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2015 3 2016年1月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

ナノダイヤモンドNV中心の電子スピン特性評価と生体応用可能性

藤原正澄, 塚原隆太, 世良佳彦, 鹿田真一, 橋本秀樹

日本物理学会講演概要集 71 1364 - 1364 2016年

記述言語：日本語出版者・発行元：一般社団法人日本物理学会

<p>ダイヤモンド窒素欠陥（NV）中心は量子情報デバイスやナノ磁気計測などへの応用が期待されている。特に生体系への応用にはダイヤモンドナノ粒子が有利である。しかしながらナノ粒子中のNV中心が示すスピン特性は表面状態の影響に敏感なため、実際の生体計測に進む前に水やpHの影響がどのようにあらわれるかを実験的に評価する必要がある。本講演では顕微分光を含めて、これらの内容を議論する。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1364

Ultrathin fiber-taper coupling with nitrogen vacancy centers in nanodiamonds at cryogenic temperatures 査読

Masazumi Fujiwara, Hong-Quan Zhao, Tetsuya Noda, Kazuhiro Ikeda, Hitoshi Sumiya, Shigeki Takeuchi

ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION IX 9762 ( 24 ) 5702 - 5705 2016年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

その他リンク： http://orcid.org/0000-0002-7845-2387

Coupling efficiency of a single light emitter coupled to a nanofiber Bragg cavity 査読

Hideaki Takashima, Andreas W. Schell, Atsushi Fukuda, Shinjiro Fujita, Yasuko Oe, Syunya Kamioka, Masazumi Fujiwara, Shigeki Takeuchi

2016 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2016年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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.

Ultrathin fiber-taper coupling with nitrogen vacancy centers in nanodiamonds at cryogenic temperatures 査読

Masazumi Fujiwara, Hong-Quan Zhao, Tetsuya Noda, Kazuhiro Ikeda, Hitoshi Sumiya, Shigeki Takeuchi

OPTICS LETTERS 40 ( 24 ) 5702 - 5705 2015年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Highly Efficient Coupling of Nanolight Emitters to a Ultra-Wide Tunable Nanofibre Cavity 査読

Andreas W. Schell, Hideaki Takashima, Shunya Kamioka, Yasuko Oe, Masazumi Fujiwara, Oliver Benson, Shigeki Takeuchi

SCIENTIFIC REPORTS 5 2015年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

17aAC-7 ナノファイバブラッグ共振器と結合した単一発光体のFDTD解析

高島秀聡, 藤原正澄, Schell A., 竹内繁樹

日本物理学会講演概要集 70 499 - 499 2015年

17aAC-8 ナノ光ファイバ結合ダイヤモンド窒素欠陥中心の光検出磁気共鳴実験

藤田慎司朗, 高島秀聡, Schell A. W., 藤原正澄, 水落憲和, 竹内繁樹

日本物理学会講演概要集 70 500 - 500 2015年

Numerical simulations of nanodiamond nitrogen-vacancy centers coupled with tapered optical fibers as hybrid quantum nanophotonic devices 査読

Mohamed Almokhtar, Masazumi Fujiwara, Hideaki Takashima, Shigeki Takeuchi

OPTICS EXPRESS 22 ( 17 ) 20045 - 20059 2014年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Numerical simulations of nanodiamond nitrogen-vacancy centers coupled with tapered optical fibers as hybrid quantum nanophotonic devices 査読

Mohamed Almokhtar, Masazumi Fujiwara, Hideaki Takashima, Shigeki Takeuchi

OPTICS EXPRESS 22 ( 17 ) 20045 - 20059 2014年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Coupling quantum dots to a nanofiber Bragg cavity

Yasuko Oe, Andreas W. Schell, Hideaki Takashima, Syunya Kamioka, Masazumi Fujiwara, Oliver Benson, Shigeki Takeuchi

Optics InfoBase Conference Papers 2014年7月

Observation of 1.2-GHz linewidth of zero-phonon-line in photoluminescence spectra of nitrogen vacancy centers in nanodiamonds using a Fabry-Perot interferometer 査読

Hong-Quan Zhao, Masazumi Fujiwara, Masayuki Okano, Shigeki Takeuchi

OPTICS EXPRESS 21 ( 24 ) 29679 - 29686 2013年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Observation of 1.2-GHz linewidth of zero-phonon-line in photoluminescence spectra of nitrogen vacancy centers in nanodiamonds using a Fabry-Perot interferometer 査読

Hong-Quan Zhao, Masazumi Fujiwara, Masayuki Okano, Shigeki Takeuchi

OPTICS EXPRESS 21 ( 24 ) 29679 - 29686 2013年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Embedded TiO2 waveguides for sensing nanofluorophores in a microfluidic channel 査読

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Kazuki Matsubara, Makusu Tsutsui, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

APPLIED PHYSICS LETTERS 101 ( 15 ) 2012年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Embedded TiO2 waveguides for sensing nanofluorophores in a microfluidic channel 査読

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Kazuki Matsubara, Makusu Tsutsui, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

APPLIED PHYSICS LETTERS 101 ( 15 ) 2012年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

ナノテーパ光ファイバを駆使した光量子デバイス

藤原正澄, 竹内繁樹

化学工業 63 ( 9 ) 25 - 30 2012年9月

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals 査読

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

JAPANESE JOURNAL OF APPLIED PHYSICS 51 ( 9 ) 2012年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals 査読

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

JAPANESE JOURNAL OF APPLIED PHYSICS 51 ( 9 ) 2012年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling 査読

Masazumi Fujiwara, Tetsuya Noda, Akira Tanaka, Kiyota Toubaru, Hong-Quan Zhao, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 17 ) 19545 - 19553 2012年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling 査読

Masazumi Fujiwara, Tetsuya Noda, Akira Tanaka, Kiyota Toubaru, Hong-Quan Zhao, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 17 ) 19545 - 19553 2012年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Suppression of fluorescence phonon sideband from nitrogen vacancy centers in diamond nanocrystals by substrate effect 査読

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 14 ) 15628 - 15635 2012年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Suppression of fluorescence phonon sideband from nitrogen vacancy centers in diamond nanocrystals by substrate effect 査読

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 14 ) 15628 - 15635 2012年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

A nanodiamond-tapered fiber system with high single-mode coupling efficiency 査読

Tim Schroeder, Masazumi Fujiwara, Tetsuya Noda, Hong-Quan Zhao, Oliver Benson, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 10 ) 10490 - 10497 2012年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

A nanodiamond-tapered fiber system with high single-mode coupling efficiency 査読

Tim Schroeder, Masazumi Fujiwara, Tetsuya Noda, Hong-Quan Zhao, Oliver Benson, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 10 ) 10490 - 10497 2012年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Suppression of Phonon Sidebands in the Spectrum of Nitrogen Vacancy Centers in Diamond Nano-Crystals 査読

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION V 8272 2012年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

Near-field coupling of a single NV center to a tapered fiber 査読

Tim Schroeder, Masazumi Fujiwara, Tetsuya Noda, Hong-Quan Zhao, Andreas W. Schell, Guenter Kewes, Oliver Benson, Shigeki Takeuchi

ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION V 8272 2012年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

Highly Efficient Coupling of Photons from Nanoemitters into Single-Mode Optical Fibers 査読

Masazumi Fujiwara, Kiyota Toubaru, Tetsuya Noda, Hong-Quan Zhao, Shigeki Takeuchi

NANO LETTERS 11 ( 10 ) 4362 - 4365 2011年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Development of microfabricated TiO2 channel waveguides 査読

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Makusu Tsutsui, Kazuki Matsubara, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

AIP ADVANCES 1 ( 3 ) 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Development of microfabricated TiO2 channel waveguides 査読

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Makusu Tsutsui, Kazuki Matsubara, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

AIP ADVANCES 1 ( 3 ) 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optical transmittance degradation in tapered fibers 査読

Masazumi Fujiwara, Kiyota Toubaru, Shigeki Takeuchi

OPTICS EXPRESS 19 ( 9 ) 8596 - 8601 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optical transmittance degradation in tapered fibers 査読

Masazumi Fujiwara, Kiyota Toubaru, Shigeki Takeuchi

OPTICS EXPRESS 19 ( 9 ) 8596 - 8601 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Phase shift spectra of a fiber-microsphere system at the single photon level 査読

Akira Tanaka, Takeshi Asai, Kiyota Toubaru, Hideaki Takashima, Masazumi Fujiwara, Ryo Okamoto, Shigeki Takeuchi

OPTICS EXPRESS 19 ( 3 ) 2278 - 2285 2011年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Phase shift spectra of a fiber-microsphere system at the single photon level 査読

Akira Tanaka, Takeshi Asai, Kiyota Toubaru, Hideaki Takashima, Masazumi Fujiwara, Ryo Okamoto, Shigeki Takeuchi

OPTICS EXPRESS 19 ( 3 ) 2278 - 2285 2011年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optical quantum circuit combining tailored optical nonlinearities 査読

Shigeki Takeuchi, Ryo Okamoto, Masazumi Fujiwara, Hong-Quan Zhao, Holger F. Hofmann, Jeremy L. O'Brien

2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011 2011年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

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

Polarization-purity spectra of a tapered-fiber-coupled microsphere cavity system at cryogenic temperatures 査読

Masazumi Fujiwara, Akira Tanakaa, Kiyota Toubarua, Hong-Quan Zhao, Hideaki Takashima, Shigeki Takeuchi

LASER RESONATORS AND BEAM CONTROL XIII 7913 2011年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

Ultrafast relaxation kinetics in β-carotene homologs having different methyl side groupsMulti-Pulse Excitation 査読

Y. Iwabuchi, K. Abe, R. Nakamura, D. Kosumi, M. Fujiwara, R. Fujii, H. Hashimoto, M. Yoshizawa

Carotenoid Science 15 26 - 29 2010年12月

Determination of the d-Tensor Components of a Single Crystal of N-Benzyl-2-methyl-4-nitroaniline (vol 46, pg 1528, 2007) 査読

Masazumi Fujiwara, Minoru Maruyama, Mitsuru Sugisaki, Hironori Takahashi, Shin-ichiro Aoshima, Richard J. Cogdell, Hideki Hashimoto

JAPANESE JOURNAL OF APPLIED PHYSICS 49 ( 11 ) 2010年11月

Erratum: Determination of the d-tensor components of a single crystal of N-benzyl-2-methyl-4-nitroaniline (Japanese Journal of Applied Physics (2007) 46 (1528)) 査読

Masazumi Fujiwara, Minoru Maruyama, Mitsuru Sugisaki, Hironori Takahashi, Shin-Ichiro Aoshima, Richard J. Cogdell, Hideki Hashimoto

Japanese Journal of Applied Physics 49 ( 11 ) 2010年11月

Determination of the d-Tensor Components of a Single Crystal of N-Benzyl-2-methyl-4-nitroaniline (vol 46, pg 1528, 2007) 査読

Masazumi Fujiwara, Minoru Maruyama, Mitsuru Sugisaki, Hironori Takahashi, Shin-ichiro Aoshima, Richard J. Cogdell, Hideki Hashimoto

JAPANESE JOURNAL OF APPLIED PHYSICS 49 ( 11 ) 119201 - 119201-1 2010年11月

Ultrafast relaxation kinetics of the dark S-1 state in all-trans-beta-carotene explored by one- and two-photon pump-probe spectroscopy 査読

Daisuke Kosumi, Kenta Abe, Hiroshi Karasawa, Masazumi Fujiwara, Richard J. Cogdell, Hideki Hashimoto, Masayuki Yoshizawa

CHEMICAL PHYSICS 373 ( 1-2 ) 33 - 37 2010年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Ultrafast relaxation kinetics of the dark S-1 state in all-trans-beta-carotene explored by one- and two-photon pump-probe spectroscopy 査読

Daisuke Kosumi, Kenta Abe, Hiroshi Karasawa, Masazumi Fujiwara, Richard J. Cogdell, Hideki Hashimoto, Masayuki Yoshizawa

CHEMICAL PHYSICS 373 ( 1-2 ) 33 - 37 2010年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Fiber-microsphere system at cryogenic temperatures toward cavity QED using diamond NV centers 査読

Hideaki Takashima, Takeshi Asai, Kiyota Toubaru, Masazumi Fujiwara, Keiji Sasaki, Shigeki Takeuchi

OPTICS EXPRESS 18 ( 14 ) 15169 - 15173 2010年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Comparison of transient grating signals from spheroidene in an organic solvent and in pigment-protein complexes from Rhodobacter sphaeroides 2.4.1 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Daisuke Kosumi, Ritsuko Fujii, Mamoru Nango, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 81 ( 24 ) 2010年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Comparison of transient grating signals from spheroidene in an organic solvent and in pigment-protein complexes from Rhodobacter sphaeroides 2.4.1 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Daisuke Kosumi, Ritsuko Fujii, Mamoru Nango, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 81 ( 24 ) 2010年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Highly sensitive femtosecond dispersive spectroscopy: Application to the ultrafast relaxation kinetics in all-trans-β-carotene 査読

D. Kosumi, K. Abe, H. Karasawa, M. Fujiwara, H. Hashimoto, M. Yoshizawa

Carotenoid Science 14 37 - 42 2009年12月

Transient grating spectroscopy in photosynthetic purple bacteria Rhodobacter sphaeroides 2.4.1 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Ritsuko Fujii, Katsunori Nakagawa, Mamoru Nango, Richard J. Cogdell, Hideki Hashimoto

JOURNAL OF LUMINESCENCE 129 ( 12 ) 1908 - 1911 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Ultrafast optical responses of beta-carotene and lycopene probed by sub-20-fs time-resolved coherent spectroscopy 査読

M. Fujiwara, M. Sugisaki, A. Gall, B. Robert, R. J. Cogdell, H. Hashimoto

JOURNAL OF LUMINESCENCE 129 ( 12 ) 1808 - 1812 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Ultrafast optical responses of beta-carotene and lycopene probed by sub-20-fs time-resolved coherent spectroscopy 査読

M. Fujiwara, M. Sugisaki, A. Gall, B. Robert, R. J. Cogdell, H. Hashimoto

JOURNAL OF LUMINESCENCE 129 ( 12 ) 1808 - 1812 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Transient grating spectroscopy in photosynthetic purple bacteria Rhodobacter sphaeroides 2.4.1 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Ritsuko Fujii, Katsunori Nakagawa, Mamoru Nango, Richard J. Cogdell, Hideki Hashimoto

JOURNAL OF LUMINESCENCE 129 ( 12 ) 1908 - 1911 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy 査読

Krzysztof Iwaszczuk, David G. Cooke, Masazumi Fujiwara, Hideki Hashimoto, Peter Uhd Jepsen

OPTICS EXPRESS 17 ( 24 ) 21969 - 21976 2009年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy 査読

Krzysztof Iwaszczuk, David G. Cooke, Masazumi Fujiwara, Hideki Hashimoto, Peter Uhd Jepsen

OPTICS EXPRESS 17 ( 24 ) 21969 - 21976 2009年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy 査読

Krzysztof Iwaszczuk, David G. Cooke, Masazumi Fujiwara, Hideki Hashimoto, Peter Uhd Jepsen

OPTICS EXPRESS 17 ( 24 ) 21969 - 21976 2009年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Ultrafast Nonlinear Optical Responses Induced by Multiphoton Excitation in All-trans-beta-Carotene: Nonresonant Excitation to the Optically Allowed S-2 State 査読

Daisuke Kosumi, Masazumi Fujiwara, Hideki Hashimoto, Masayuki Yoshizawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 ( 10 ) 104715 - 104715-5 2009年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 (> 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

Ultrafast Nonlinear Optical Responses Induced by Multiphoton Excitation in All-trans-beta-Carotene: Nonresonant Excitation to the Optically Allowed S-2 State 査読

Daisuke Kosumi, Masazumi Fujiwara, Hideki Hashimoto, Masayuki Yoshizawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 ( 10 ) 104715 - 104715 2009年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 (> 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

Ultrafast Nonlinear Optical Responses Induced by Multiphoton Excitation in All-trans-beta-Carotene: Nonresonant Excitation to the Optically Allowed S-2 State 査読

Daisuke Kosumi, Masazumi Fujiwara, Hideki Hashimoto, Masayuki Yoshizawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 ( 10 ) 2009年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 (> 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

Optimized terahertz-wave generation using BNA-DFG 査読

Katsuhiko Miyamoto, Seigo Ohno, Masazumi Fujiwara, Hiroaki Minamide, Hideki Hashimoto, Hiromasa Ito

Optics Express 17 ( 17 ) 14832 - 14838 2009年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optimized terahertz-wave generation using BNA-DFG 査読

Katsuhiko Miyamoto, Seigo Ohno, Masazumi Fujiwara, Hiroaki Minamide, Hideki Hashimoto, Hiromasa Ito

OPTICS EXPRESS 17 ( 17 ) 14832 - 14838 2009年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Optimized terahertz-wave generation using BNA-DFG 査読

Katsuhiko Miyamoto, Seigo Ohno, Masazumi Fujiwara, Hiroaki Minamide, Hideki Hashimoto, Hiromasa Ito

OPTICS EXPRESS 17 ( 17 ) 14832 - 14838 2009年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Excitation-energy dependence of transient grating spectroscopy in beta-carotene 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Selvakumar V. Nair, Harry E. Ruda, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 80 ( 3 ) 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Excitation-energy dependence of transient grating spectroscopy in beta-carotene 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Selvakumar V. Nair, Harry E. Ruda, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 80 ( 3 ) 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

The dependence of the ultrafast relaxation kinetics of the S-2 and S-1 states in beta-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies 査読

Daisuke Kosumi, Masazumi Fujiwara, Ritsuko Fujii, Richard J. Cogdell, Hideki Hashimoto, Masayuki Yoshizawa

JOURNAL OF CHEMICAL PHYSICS 130 ( 21 ) 2009年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 -> S-x -> S-1 -> 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

The dependence of the ultrafast relaxation kinetics of the S-2 and S-1 states in beta-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies 査読

Daisuke Kosumi, Masazumi Fujiwara, Ritsuko Fujii, Richard J. Cogdell, Hideki Hashimoto, Masayuki Yoshizawa

JOURNAL OF CHEMICAL PHYSICS 130 ( 21 ) 2009年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 -> S-x -> S-1 -> 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

Specific Channel of Energy Dissipation in Carotenoids: Coherent Spectroscopic Study 査読

Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Andrew Gall, Bruno Robert, Richard J. Cogdell, Hideki Hashimoto

ULTRAFAST PHENOMENA XVI 92 367 - + 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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.

Ultrafast coherent vibronic oscillations in regioregular poly(3-alkylthiophene) 査読

Katsuichi Kanemoto, Mitsuru Sugisaki, Masazumi Fujiwara, Tsutomu Karasawa, Hideki Hashimoto

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, SUPPL 1 6 ( S1 ) S46 - S49 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

Third-order optical nonlinearity of β-carotene homologues 査読

Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Kazuhiro Yanagi, Andrew Gall, Bruno Robert, Richard, J. Cogdell, Hideki Hashimoto

Physica Status Solidi C 6 ( S1 ) S31 - S33 2009年

Spectrally-resolved transient grating signals from β-carotene in benzene solution 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Selvakumar V. Nair, Harry E. Ruda, Richard, J. Cogdell, Hideki Hashimoto

Physica Status Solidi C 6 ( S1 ) S34 - S37 2009年

Large third-order optical nonlinearity realized in symmetric nonpolar carotenoids 査読

Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Kazuhiro Yanagi, Andrew Gall, Bruno Robert, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 78 ( 16 ) 2008年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Large third-order optical nonlinearity realized in symmetric nonpolar carotenoids 査読

Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Kazuhiro Yanagi, Andrew Gall, Bruno Robert, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 78 ( 16 ) 2008年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Energy dissipation in the ground-state vibrational manifolds of beta-carotene homologues: A sub-20-fs time-resolved transient grating spectroscopic study 査読

Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Andrew Gall, Bruno Robert, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 77 ( 20 ) 2008年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Energy dissipation in the ground-state vibrational manifolds of beta-carotene homologues: A sub-20-fs time-resolved transient grating spectroscopic study 査読

Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Andrew Gall, Bruno Robert, Richard J. Cogdell, Hideki Hashimoto

PHYSICAL REVIEW B 77 ( 20 ) 10 2008年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Widely tunable terahertz-wave generation using an N-benzyl-2-methyl-4- nitroaniline crystal 査読

Katsuhiko Miyamoto, Hiroaki Minamide, Masazumi Fujiwara, Hideki Hashimoto, Hiromasa Ito

Optics Letters 33 ( 3 ) 252 - 254 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

その他リンク： http://orcid.org/0000-0002-7845-2387

Four-wave mixing signals from beta-carotene and its n=15 homologue 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Kazuhiro Yanagi, Richard J. Cogdell, Hideki Hashimoto

PHOTOSYNTHESIS RESEARCH 95 ( 2-3 ) 299 - 308 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Widely tunable terahertz-wave generation using an N-benzyl-2-methyl-4-nitro aniline crystal 査読

Katsuhiko Miyamoto, Hiroaki Minamide, Masazumi Fujiwara, Hideki Hashimoto, Hiromasa Ito

OPTICS LETTERS 33 ( 3 ) 252 - 254 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Four-wave mixing signals from beta-carotene and its n=15 homologue 査読

Mitsuru Sugisaki, Masazumi Fujiwara, Kazuhiro Yanagi, Richard J. Cogdell, Hideki Hashimoto

PHOTOSYNTHESIS RESEARCH 95 ( 2-3 ) 299 - 308 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Coherent tunable monochromatic Terahertz-wave generation using N-Benzyl-2-methyl-4-nitroaniline (BNA) crystal 査読

Katsuhiko Miyamoto, Hiroaki Minamide, Masazumi Fujiwara, Hideki Hashimoto, Hiromasa Ito

NONLINEAR FREQUENCY GENERATION AND CONVERSION: MATERIALS, DEVICES, AND APPLICATIONS VII 6875 2008年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

Determination of the d-tensor components of a single crystal of N-benzyl-2-methyl-4-nitroaniline 査読

Masazumi Fujiwara, Minoru Maruyama, Mitsuru Sugisaki, Hironori Takahashi, Shin-ichiro Aoshima, Richard J. Cogdell, Hideki Hashimoto

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 ( 4A ) 1528 - 1530 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Second order nonlinear optical properties of the single crystal of N-benzyl 2-methyl-4-nitroaniline: Anomalous enhancement of the d(333) component and its possible origin 査読

Masazumi Fujiwara, Kazuhiro Yanagi, Minoru Maruyama, Mitsuru Sugisaki, Kazuyoshi Kuroyanagi, Hironori Takahashi, Shin-ichiro Aoshima, Yutaka Tsuchiya, Andrew Gall, Hideki Hashimoto

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 ( 11 ) 8676 - 8685 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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) > 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

Second order nonlinear optical properties of the single crystal of N-benzyl 2-methyl-4-nitroaniline: Anomalous enhancement of the d(333) component and its possible origin 査読

Masazumi Fujiwara, Kazuhiro Yanagi, Minoru Maruyama, Mitsuru Sugisaki, Kazuyoshi Kuroyanagi, Hironori Takahashi, Shin-ichiro Aoshima, Yutaka Tsuchiya, Andrew Gall, Hideki Hashimoto

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 ( 11 ) 8676 - 8685 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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) > 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

Determination of refractive indices and absorption coefficients of highly purified N-benzyl-2-methyl-4-nitroaniline crystal in terahertz frequency regime 査読

Kazuyoshi Kuroyanagi, Masazumi Fujiwara, Hideki Hashimoto, Hironori Takahashi, Shin-ichiro Aoshima, Yutaka Tsuchiya

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 ( 29-32 ) L761 - L764 2006年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

All organic terahertz electromagnetic wave emission and detection using highly purified N-benzyl-2-methyl-4-nitroaniline crystals 査読

K Kuroyanagi, M Fujiwara, H Hashimoto, H Takahashi, SI Aoshima, Y Tsuchiya

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 ( 5A ) 4068 - 4073 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：INST PURE APPLIED PHYSICS

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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