Browsing by Author "Kao, Chih-Hsien"

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Beat of Frequency Modes with an Artificial Negative Frequency in Spectrogram Analysis
(2010-12-05)
Yabushita, Atsushi
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Kao, Chih-Hsien
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Lee, Yu-Hsien
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Kobayashi, Takayoshi
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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"
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
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Kao, Chih-Hsien
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Lee, Yu-Hsien
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Kobayashi, Takayoshi
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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
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.
Regioselective Piperidine-Catalyzed Tandem Imination-Isocyanate Annulation to Fused Tricyclic Triazines
(2014-05-01)
Barve, Indrajeet J.
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Chen, Chih-Hau
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Kao, Chih-Hsien
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Sun, Chung-Ming
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應用化學系
A novel tandem imination-isocyanate-mediated annulation was explored. Ionic liquid-immobilized 2-aminobenzimidazoles react sequentially with aldehydes and isocyanates to give highly functionalized benzimidazole-embedded triazines. The second-stage transformation revealed that the formation of triazinone functionality is entirely regioselective to allow rapid assembly of biologically interesting tricyclic skeletons. In conjunction with the application of microwave irradiation and IL support, this method provides an efficient route to access substituted benzoimidazotriazines.
Regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats on an ionic liquid support
(2016-01-01)
Chen, Li-Hsun
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Kao, Chih-Hsien
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Dhole, Sandip
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Barve, Indrajeet J.
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Shen, Li-Ching
An ionic liquid (IL) supported, regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats under microwave conditions was reported. The IL-immobilized aromatic amines were reacted with various ketones and aliphatic aldehydes using an unconventional Pictet-Spengler reaction to generate polycyclic imidazo[1,5-a]quinoxalines. Alternatively, aromatic aldehydes afforded auto-oxidized imidazo[1,5-a]quinoxalines first which further converted to novel methyl N-phenylbenzimidats unexpectedly during the cleavage of the IL-support. In the reported strategy, rapidness is achieved through microwave conditions while the IL-support assists purification by simple precipitation.
Regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats on an ionic liquid support
(2016-01-01)
Chen, Li-Hsun
;
Kao, Chih-Hsien
;
Dhole, Sandip
;
Barve, Indrajeet J.
;
Shen, Li-Ching
An ionic liquid (IL) supported, regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats under microwave conditions was reported. The IL-immobilized aromatic amines were reacted with various ketones and aliphatic aldehydes using an unconventional Pictet-Spengler reaction to generate polycyclic imidazo[1,5-a]quinoxalines. Alternatively, aromatic aldehydes afforded auto-oxidized imidazo[1,5-a]quinoxalines first which further converted to novel methyl N-phenylbenzimidats unexpectedly during the cleavage of the IL-support. In the reported strategy, rapidness is achieved through microwave conditions while the IL-support assists purification by simple precipitation.
Ultrafast photoexcited dynamics probe of blends of conjugated polymer poly{bi(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione} and fullerenes for photovoltaic applications with broadband sub-10-fs visible pulse
(2016-03)
Kao, Chih-Hsien
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Yabushita, Atsushi
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Su, Yu-Wei
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Wei, Kung-Hwa
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Lee, Yu-Hsien
Conjugated polymers have been widely studied as active materials for organic solar cells, which are a promising replacement for silicon solar cells. A novel electron donor polymer of poly{bi(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione} (PBTTPD) blended with an electron acceptor, [6,6]-phenyl C-71 butyric acid methyl ester (PC71BM), gave a device power conversion efficiency as high as 7.3%. In the present work, we performed time-resolved absorption change spectroscopy at various mixture ratios of PC71BM in the PBTTPD/PC71BM blend. Among the obtained time constants, the shortest (60 fs) and the longest (500 fs and 15 ps) were assigned to the production and relaxation of charge-transfer (CT) states, respectively. The PC71BM blended with PBTTPD was found to suppress interchain carrier transport and increase intrachain carrier transport. The prolonged lifetime of the CT state in the equally blended PBTTPD/PC71BM film increases the probability of charge separation and thus increases the power conversion efficiency of the device. (C) 2016 The Japan Society of Applied Physics