研究者詳細 - 藤原　正澄

論文 - 藤原　正澄

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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

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