研究者詳細 - 藤原　正澄

論文 - 藤原　正澄

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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

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