Browsing by Author "Yabushita, Atsushi"

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A new reaction mechanism of Claisen rearrangement induced by few-optical-cycle pulses: Demonstration of nonthermal chemistry by femtosecond vibrational spectroscopy
(2013)
Iwakura, Izumi
;
Yabushita, Atsushi
;
Liu, Jun
;
Okamura, Kotaro
;
Kezuka, Satoko
Time-resolved vibration spectroscopy is the only known way to directly observe reaction processes. In this work, we measure time-resolved vibration spectra of the Claisen rearrangement triggered and observed by few-optical-cycle pulses. Changes in molecular structure during the reaction, including its transition states (TSs), are elucidated by observing the transient changes of molecular vibration wavenumbers. We pump samples with visible ultrashort pulses of shorter duration than the molecular vibration period, and with photon energies much lower than the minimum excitation energy of the sample. The results indicate that the "nonthermal Claisen rearrangement" can be triggered by visible few-optical-cycle pulses exciting molecular vibrations in the electronic ground state of the sample, which replaces the typical thermal Claisen rearrangement.
Beamlike photon pairs entangled by a 2 x 2 fiber
(2011-08-01)
Lo, Hsin-Pin
;
Yabushita, Atsushi
;
Luo, Chih-Wei
;
Chen, Pochung
;
Kobayashi, Takayoshi
Polarization-entangled photon pairs have been widely used as a light source of quantum communication. The polarization-entangled photon pairs are generally obtained at the crossing points of the light cones that are generated from a type-II nonlinear crystal. However, it is hard to pick up the photon pairs coming out from the crossing points because of their invisible wavelength and low intensity. In our previous work, we succeeded in generating polarization-entangled photon pairs by overlapping two light paths for the photon-pair generation. The photon pairs could be entangled in all of the generated photon pairs without clipping the crossing points, even with some difficulty in its alignment to overlap the two light paths. In this paper, we have developed an optical system which generates polarization-entangled photon pairs using a beamlike photon pair, without the difficulty in alignment. The measured results show that the photon pairs generated in the system are entangled in their polarizations.
Beamlike photon-pair generation for two-photon interference and polarization entanglement
(2011-02-14)
Lo, Hsin-Pin
;
Yabushita, Atsushi
;
Luo, Chih-Wei
;
Chen, Pochung
;
Kobayashi, Takayoshi
Beamlike photon pairs were generated by spontaneous parametric down-conversion using a type-II beta-BaB2O4 crystal. A pump laser generated photon pairs when it transmitted through the crystal and was reflected back into the crystal by a mirror to generate more photon pairs. The photon pairs generated when the pump laser first transmitted through the crystal (first photon pairs) were also reflected back into the crystal to overlap with the light path of the photon pairs generated in the second transmission of the pump laser through the crystal (second photon pairs). We observed interference between the first and second photon pairs modulated with a half period of the wavelength of the photon pairs, which demonstrates two-photon interference using the beamlike photon pairs. The fringe period confirms that the observed interference is not classical interference but quantum two-photon interference. Through rotating the angles of quarter-wave plates in the light paths of the photon pairs, we generated beamlike photon pairs with entangled polarization. The phase between the first and second photon pairs could be tuned by changing the position of mirrors reflecting the pump pulses and photon pairs. The fringes of coincidence counts showed that the beamlike photon pairs have polarization entanglement.
Beat of Frequency Modes with an Artificial Negative Frequency in Spectrogram Analysis
(2010-12-05)
Yabushita, Atsushi
;
Kao, Chih-Hsien
;
Lee, Yu-Hsien
;
Kobayashi, Takayoshi
;
電子物理學系
Spectrograms have been used for time-resolved analysis of Fourier power spectra in various fields We have performed spectrogram analysis for two neighboring modes and a low frequency mode changing gate width of the time gate function The obtained spectrogram of the former showed both amplitude and frequency modulations between two neighboring modes A contamination appearing on the spectrogram of the latter reflects an artifact showing beat between the signal mode and a negative frequency mode whose sign was inverted from the signal mode Surprising results from the amplitude and phase modulations were observed in the simulation even in the case of single mode This puzzling result was explained in terms of the interference between the single mode and the "negative" frequency composing the single mode with the corresponding positive frequency"
Carrier-Envelope Phase of Single-Cycle Pulses Generated Through Two-Color Laser Filamentation
(2015-01-01)
Fuji, Takao
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Nomura, Yutaka
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Wang, Yu-Ting
;
Yabushita, Atsushi
;
Luo, Chih-Wei
Carrier-envelope phase (CEP) of the single-cycle pulses generated through two-color filamentation has been investigated. It has been found that the phase of high frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low frequency components takes only two discrete values. To our knowledge, such behavior of the phase has never been discussed before. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination.
Carrier-envelope phase of ultrashort pulses generated by optical rectification process
(2013-01-01)
Fuji, Takao
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Nomura, Yutaka
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Wang, Yu-Ting
;
Yabushita, Atsushi
;
Luo, Chih-Wei
Chirped molecular vibration in a stilbene derivative in solution
(2007-11-15)
Colonna, Anne
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Yabushita, Atsushi
;
Iwakura, Izumi
;
Kobayashi, Takayoshi
;
電子物理學系
The wave packet dynamics of 4-methoxy-4 '-nitrostilbene in solution was studied by femtosecond pump-probe spectroscopy. Transient changes in absorbance exhibit oscillations, which reflect vibrational motions on the ground-state potential surface. Modification of this oscillatory feature in three different solvents (benzene, methanol, and acetonitrile) can be explained in term of the strength of hydrogen bonding and the stabilization of charge-transfer state, confirmed by steady-state absorption and fluorescence spectra. (c) 2007 Elsevier B.V. All rights reserved.
Controlling the carrier-envelope phase of single-cycle mid-infrared pulses with two-color filamentation
(2015-02-01)
Nomura, Yutaka
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Wang, Yu-Ting
;
Yabushita, Atsushi
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Luo, Chih-Wei
;
Fuji, Takao
Carrier-envelope phase (CEP) of single-cycle pulses generated through two-color filamentation has been investigated. We have observed a particular behavior of the phase: the phase of high-frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low-frequency components takes only two discrete values. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination. We have found out that such a phase behavior is a unique feature of single-cycle pulses generated with a passive CEP stabilization scheme. (C) 2015 Optical Society of America
Development and demonstration of table-top synchronized fast-scan femtosecond time-resolved spectroscopy system by single-shot scan photo detector array
(2015-07-01)
Yabushita, Atsushi
;
Kao, Chih-Hsien
;
Lee, Yu-Hsien
;
Kobayashi, Takayoshi
;
電子物理學系
Ultrafast dynamics is generally studied by pump-probe method with laser pulse, which scans optical delay by motorized stage step by step. Using ultrashort laser pulse shorter than typical molecular vibration periods, the pump-probe measurement can study both of electronic dynamics and vibration dynamics simultaneously. The probe wavelength dependence of the ultrafast electronic and vibration dynamics (UEVD) helps us to distinguish the signal contributions from the dynamics of the electronic ground state and that of the electronic excited states, which elucidates primary reaction mechanism after photoexcitation. Meanwhile, the measurement time of UEVD spectroscopy takes too long time to be used in realistic application. In our previous work, we have developed multi-channel lock-in amplifying (MLA) detectors to study UEVD at all probe wavelengths simultaneously, and synchronized it with laser and fast-scan delay stage to scan the data in five seconds. It enabled us to study UEVD spectroscopy even for photo-fragile materials. However, the home-made MLA detectors required for the measurement is expensive and massive in size and weight, thus not suitable for general researchers in the field of ultrafast time-resolved spectroscopy. In the present work, we have developed a table-top synchronized fast-scan femtosecond time-resolved spectroscopy system using single shot scan line CCD. This system measures time-resolved trace at all probe wavelengths simultaneously in five seconds. The CCD-based fast-scan time-resolved spectroscopy system enables us to study ultrafast dynamics of various materials even biomaterials, which have been thought to be hard or even impossible to be studied in previous methods. (C) 2015 The Japan Society of Applied Physics
Development of a multiplex fast-scan system for ultrafast time-resolved spectroscopy
(2010-06-01)
Yabushita, Atsushi
;
Lee, Yu-Hsien
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
A fast-scan method was developed to obtain time-resolved signals with femtosecond resolution over a picosecond range on the fly and in real time. Traditional fast-scan methods collect data at each probe wavelength one by one, which is time consuming and thus not possible for the study of photofragile materials. In this work, we have developed a system that performs fast scans with multiplex detection. Ultrafast time-resolved spectroscopy was demonstrated using the newly developed system. Femtosecond laser pulses have been used for pump-probe studies of ultrafast processes in various materials, and both electronic relaxation and vibrational dynamics have been studied. However, experiments have been limited in sensitivity and reliability because they are affected by the long-term instability of the ultrashort laser pulses and by the fragility of the samples. The instability of the sources hinders precise determination of electronic decay dynamics and introduces systematic errors. The fragility of the samples reduces their amount or concentration, and can lead to contamination of the materials even if they were pure before the measurement. These effects make it difficult to obtain reproducible and reliable experimental data. In the present work, we have developed a fast-scan pump-probe spectroscopic system that can complete a set of measurements in less than 2 min. Quantitative estimates of the signal reproducibility demonstrate that these measurements provide higher reproducibility and reliability than conventional measurements. (C) 2010 American Institute of Physics. [doi:10.1063/1.3455809]
Development of Novel Reactions Induced by Coherent Molecular Vibrational Excitation and Direct Observation of Molecular Structural Change during "Thermal" Reactions
(2016-03-15)
Iwakural, Izumi
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Yabushita, Atsushi
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電子物理學系
;
Department of Electrophysics
Femtochemistry began from the observation of transition states (TSs) in gas-phase photoreactions. Later developments in visible ultrashort laser pulses enabled visualization of real-time changes in the molecular vibrational modes during photo reactions, including those in the liquid phase. However, TSs in thermal reactions could still not be studied, because the conventional femtosecond laser pulse cannot trigger chemical reactions in the electronic ground state. In the present work, a visible ultrashort laser pulse was used to cause an induced Raman process, whereby Raman active molecular vibrational modes were excited in the electronic ground states, which triggers the reaction induced by coherent molecular vibrational excitation in the electronic ground state just after photo excitation. Using the "reaction by coherent molecular vibration", we have successfully observed the TSs in a "thermal" reaction, thermal Claisen rearrangement.
Direct Observation of Molecular Structural Change during Intersystem Crossing by Real-Time Spectroscopy with a Few Optical Cycle Laser
(2009-04-20)
Iwakura, Izumi
;
Kobayashi, Takayoshi
;
Yabushita, Atsushi
;
電子物理學系
;
Department of Electrophysics
Ultrafast spectroscopy by a sub-5 fs pulse laser was applied to the simultaneous study of electronic relaxation and vibrational dynamics in Ru(II)(TPP)(CO). The electronic lifetimes of (1)Q(x(1,0))(pi,pi*) and (1)Q(x(0,0))(pi,pi*) were determined to be 230 +/- 70 fs and 1150 +/- 260 fs, respectively. The spectrogram shows the time dependent changes in the vibrational spectrum associated with the spin state change from the Franck-Condon state in the excited singlet state to the triplet state via the curve crossing point between the singlet and triplet potential surfaces. The time constant of the intersystem crossing process was determined to be about 1.0 ps from observed electronic relaxation and vibrational dynamics reflecting the transition from the singlet to triplet electronic excited state.
Direct observation of the change in transient molecular structure of 9,9'-bianthryl using a 10 fs pulse UV laser
(2018-08-17)
Hashimoto, Sena
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Yabushita, Atsushi
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Kobayashi, Takayoshi
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Okamura, Kotaro
;
Iwakura, Izumi
Photoexcitation of 9,9'-bianthryl has been considered to produce a locally excited (LE) state and then a charge transfer (CT) state by intramolecular charge transfer (ICT) in polar solvents. In contrast, the CT state is considered to be unstable in non-polar solvents and triggers a dipole flip-flop between the two anthracene rings. The central C-C bond between the two anthracene rings is considered to twist during relaxation in the LE state and CT state, and this was visualized in the present work using an ultrashort ultraviolet (UV) pulse. The C-C stretching frequency was recovered in a period of ca. 500 fs, which implies that the C-C bond undergoes repeated torsion back and forth in the electronic excited state. Investigation of samples in a polar solvent and a non-polar solvent indicated that ICT does not affect the torsion around the central C-C bond. (C) 2018 Elsevier B.V. All rights reserved.
Dynamics of vibrational and electronic coherences in the electronic excited state studied in a negative-time range
(2009-11-06)
Kobayashi, Takayoshi
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Yabushita, Atsushi
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電子物理學系
;
Department of Electrophysics
Femtosecond pump-probe spectroscopy signals in a negative-time range (i.e., when the probe pulse precedes pump pulse) were analyzed to study the dynamics of electronic and vibrational coherences in the photodissociation of oxyhemoglobin. The decay time of the electronic coherence between the ground and Q-band electronic states is found to be 45 +/- 5 fs. The dephasing times of the vibrational modes of several frequencies in the ground state have been determined. Those in the excited state are found to be similar to 26 fs. The absence or presence of the modes in the negative-time range due to the excited state wavepacket is explained in terms of the mode coupling strength. (C) 2009 Elsevier B.V. All rights reserved.
Environment-Dependent Ultrafast Photoisomerization Dynamics in Azo Dye
(2011-10-27)
Hsu, Chun-Chih
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Wang, Yu-Ting
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Yabushita, Atsushi
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Luo, Chih-Wei
;
Hsiao, Yi-Nan
Azoaromatic dyes have been extensively investigated over the past decade due to their potential use in a variety of optical devices that exploit their ultrafast photoisomerization processes. Among the azoaromatic dyes, Disperse Red 19 is a commercially available azobenzene nonlinear optical chromophore with a relatively high ground-state dipole moment. In the present study, we used ultrafast time-resolved spectroscopy to clarify the dynamics of a push-pull substituted azobenzene dye. Solution and film samples exhibited different ultrafast dynamics, indicating that the molecular environment affects the photoisomerization dynamics of the dye.
Experimental verification of multidimensional quantum steering
(2018-03-01)
Li, Che-Ming
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Lo, Hsin-Pin
;
Chen, Liang-Yu
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Yabushita, Atsushi
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電子物理學系
Quantum steering enables one party to communicate with another remote party even if the sender is untrusted. Such characteristics of quantum systems not only provide direct applications to quantum information science, but are also conceptually important for distinguishing between quantum and classical resources. While concrete illustrations of steering have been shown in several experiments, quantum steering has not been certified for higher dimensional systems. Here, we introduce a simple method to experimentally certify two different kinds of quantum steering: Einstein-Podolsky-Rosen (EPR) steering and single-system (SS) steering (i.e., temporal steering), for dimensionality (d) up to d = 16. The former reveals the steerability among bipartite systems,whereas the latter manifests itself in single quantum objects. We use multidimensional steering witnesses to verify EPR steering of polarization-entangled pairs and SS steering of single photons. The ratios between the measured witnesses and the maximum values achieved by classical mimicries are observed to increase with.. for both EPR and SS steering. The designed scenario offers a new method to study further the genuine multipartite steering of large dimensionality and potential uses in quantum information processing. (c) 2017 Elsevier B.V. All rights reserved.
Experimental violation of Bell inequalities for multi-dimensional systems
(2016-02-26)
Lo, Hsin-Pin
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Li, Che-Ming
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Yabushita, Atsushi
;
Chen, Yueh-Nan
;
Luo, Chih-Wei
Quantum correlations between spatially separated parts of a d-dimensional bipartite system (d >= 2) have no classical analog. Such correlations, also called entanglements, are not only conceptually important, but also have a profound impact on information science. In theory the violation of Bell inequalities based on local realistic theories for d-dimensional systems provides evidence of quantum nonlocality. Experimental verification is required to confirm whether a quantum system of extremely large dimension can possess this feature, however it has never been performed for large dimension. Here, we report that Bell inequalities are experimentally violated for bipartite quantum systems of dimensionality d=16 with the usual ensembles of polarization-entangled photon pairs. We also estimate that our entanglement source violates Bell inequalities for extremely high dimensionality of d>4000. The designed scenario offers a possible new method to investigate the entanglement of multipartite systems of large dimensionality and their application in quantum information processing.
Exploring steering effects using Bell tests
(2014-02-18)
Lo, Hsin-Pin
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Yabushita, Atsushi
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Hsu, Li-Yi
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電子物理學系
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Department of Electrophysics
We study the interconnection among steering, uncertainty, and quantum correlation. The practical steering criteria for bipartite quantum entanglement are proposed using the multiple applications of the Maassen-Uffink uncertainty relation. The results show that distant steering causes less uncertainty than that in any local-hidden-variable theories. The reduction of uncertainty in the quantum steering of entangled states leads to quantum correlation. The steering visibility for the mixed states is also discussed. The experimental results on the proposed steering criteria are reported.
Fs photo-isomerization in bacteriorhodopsin by few-cycle pulses
(2008-05-01)
Kobayashi, Takayoshi
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Yabushita, Atsushi
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電子物理學系
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Department of Electrophysics
We have build up non-collinear optical parametric amplifier (NOPA) laser system with adaptive pulse tailoring, which enables to generate sub-4-fs laser pulses. Using the ultrashort laser pulses generated by NOPA, we have performed pump-probe measurement of bacteriorhodopsin (bR) using ultrashort pulses, which can observe real-time frequencies of molecular vibrations. Both of the spectra of pump and probe pulses are nearly the same and cover a spectral range from 500 to 710 nm with a nearly constant phase. The time-gated Fourier transform of the measured absorbance change trace revealed that the frequency of the C = C stretching mode was modulated along with the torsion motion around C-13=C-14 during the photoisomerization of bR. It shows the bond length Of C13=C14 is modulated on the deformation around C-13=C-14 during the photoisomerization. The hydrogen-out-of-plane (HOOP) mode and the in-plane C = C-H bending mode coupled with C-C stretching mode are found to be intermixed with each other in the same period of the torsion motion. It also shows us the real-time conformation change of the molecule, which makes both of the modes indistinguishable. (C) 2007 Elsevier B.V. All rights reserved.
Generation of multi-color carrier-envelope phase locked pulse with continuous color tunability
(2014-03-15)
Yabushita, Atsushi
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Juang, Ding-Yi
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Kao, Chih-Hsien
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Baltuska, Andrius
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Kobayashi, Takayoshi
Several methods exist to lock carrier envelope phase (CEP), which is generally not locked in common laser systems. Our previous work succeeded passive lock of CEP by using a technique of non-collinear optical parametric amplifier. In the present work, we have proposed and demonstrated two schemes to generate multi-color CEP-locked beams using the non-collinear optical parametric amplifier. In the first scheme, spatial filter in the spatially dispersed seed light was used to generate three-color CEP-locked pulse demonstrating ifs arbitral color tunability. In the second scheme, parabolic chirp was introduced on the seed pulse to generate two color CEP-locked pulses with continuous color tunability. (C) 2013 Elsevier B.V. All rights reserved.