Browsing by Author "Yabushita, A."

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A wide range THz pulses generation in ZnTe crystals
(2012)
Ku, S. A.
;
Tu, C. -M.
;
Luo, C. W.
;
Wu, K. H.
;
Yabushita, A.
The THz generation in ZnTe crystals by widely varying pumping fluences is reported. Some abnormal nonlinear effects were observed including the evolution of THz spectra and the phase shift of temporal waveforms. Moreover, the THz efficiency can enhance again at high pumping fluence due to the saturation of free carrier.
Chirped molecular vibration after impulsive Raman excitation in a stilbene derivative molecule in solution
(2007)
Kobayashi, T.
;
Colonna, A.
;
Yabushita, A.
;
Iwakura, I.
;
Tokunaga, E.
The vibrational dynamics in 4-methoxy-4\'-nitrostilbene in a condensed phase was studied by fermosecond pump-probe spectroscopy and quantum-chemical calculation. Transient changes in absorbance due to bleaching exhibit oscillations reflecting chirped molecular vibrational on the potential surface.
Chirped-pulse upconversion of mid-infrared pulses with four-wave difference frequency generation in gases
(2013)
Fuji, T.
;
Nomura, Y.
;
Wang, Y-T
;
Yabushita, A.
;
Luo, C-W
Single-shot detection of mid-infrared spectra from 250 to 5500 cm(-1) with 5 cm(-1) resolution was demonstrated by using chirped-pulse upconversion with four-wave difference frequency generation in gases
Excitonic and vibrational nonlinear processes in a polydiacetylene studied by a few-cycle pulse laser
(2008-06-30)
Kobayashi, T.
;
Iwakura, I.
;
Yabushita, A.
;
電子物理學系
;
Department of Electrophysics
High-density excitation of exciton induces the faster decay of absorbance change due to exciton-exciton interaction originated from the Auger recombination process. Experimental results clarified the dynamics of the exciton and the bimolecular quenching rate and the jump rate of exciton were determined to be 5.2 x 10(-9) cm(3) s(-1) and 5.2 x 10(-9) s(-1), respectively. The intensity modulation of electronic transition under high-density excitation with sub-5-fs pulse was analyzed to observe the Fourier power spectrum of the molecular vibration modes and revealed the existence of a combination tone (2726 cm(-1)) of the C-C (1241 cm(-1)) and the C=C (1485 cm(-1)) stretching modes. This indicates that the highly excited state induced by the Auger process results in the fusion of vibrational quantum states. Difference frequency generation of the vibrational modes also takes place in the same process due to the fission of the vibrational quanta stimulated by the interaction of the two vibrational modes. It was also found that the intensities of several prominent peaks corresponding to the modes of C=C and C-C stretching were proportional to the squared intensity of the probe pulse. Furthermore, the frequencies of the modes were shifted to low frequencies at high probe intensity. The process can be considered to be fifth-order cascaded Raman scattering via real excitation of vibronic excitons.
Real-time observation of carbon double bond transformation during photo-isomerization of bacteriorhodopsin
(2007)
Yabushita, A.
;
Kobayashi, T.
;
電子物理學系
;
Department of Electrophysics
The modulation in the frequency of the, C=C stretching mode was observed by pump-probe measurement. The period of the modulation, corresponding to the modulation of the mean C=C bond length, was found to be similar to 200fs.
Saturation of the free carrier absorption in ZnTe crystals
(2013-06-17)
Ku, S. A.
;
Tu, C. M.
;
Chu, W. -C.
;
Luo, C. W.
;
Wu, K. H.
This study systematically investigates the influence of free carriers on the generation of THz in ZnTe crystals, over a wide range of pumping fluences. As the pumping fluence is increased (< 6.36 mJ/cm(2)), the concentration of free carriers gradually increases and the THz output power is saturated, as clearly demonstrated by the time delay in the THz temporal waveforms, the changes in the THz spectral weight and the red-shift in the PL spectra. For high pumping fluences (> 6.36 mJ/cm(2)), spectacularly, there is a significant quadratic increase in the THz output power when the pumping fluence is increased, as well as at low pumping fluences of < 0.58 mJ/cm(2), because of the saturation of free carriers. (C) 2013 Optical Society of America
Single-shot detection of mid-infrared spectra by chirped-pulse upconversion with four-wave difference frequency generation in gases
(2013-07-29)
Nomura, Y.
;
Wang, Y. -T.
;
Kozai, T.
;
Shirai, H.
;
Yabushita, A.
Single-shot detection of ultrabroadband mid-infrared spectra was demonstrated by using chirped-pulse upconversion technique with four-wave difference frequency generation in gases. Thanks to the low dispersion of the gas media, the bandwidth of the phase matching condition of the upconversion process becomes very broad and the entire mid-infrared spectrum spanning from 200 to 5500 cm(-1) was upconverted by using a 10 ps chirped pulse to visible wavelength radiation, which was detected with a conventional visible dispersive spectrometer. This method was demonstrated by the successful measurement of infrared absorption spectra of organic polymer films. (C) 2013 Optical Society of America
Spectral Shaping and Continuous Tuning of Multi-color Carrier-Envelope Phase Locked Pulse
(2015-01-01)
Yabushita, A.
;
Kao, C. -H.
;
Kobayashi, T.
;
電子物理學系
;
Department of Electrophysics
We have proposed and demonstrated two schemes to generate multi-color CEP-locked beams by using the NOPA. In the first scheme, a spatial filter in the spectrally dispersed seed light made the seed spectrum have three peaks, and the generated idler beam also had three peaks. The spectrum of the CEP-locked pulse can be shaped into arbitral spectral shape. In the second scheme, parabolic chirp was introduced on the seed pulse to generate two-color CEP-locked pulse whose colors are tunable.
Ultrafast Dynamics in Optimally Doped YBa(2)Cu(3)O(7-delta) Observed with White Light Pump-probe Spectroscopy
(2011-01-01)
Wang, Y. T.
;
Lee, Y. H.
;
Chen, Y. -J.
;
Tang, W. T.
;
Luo, C. W.
The quasiparticle relaxation dynamics in optimally doped (001) YBa(2)Cu(3)O(7-delta) thin films were measured at various temperatures by white light pump-probe technique. The 2D ultrafast spectroscopy with broadband (similar to 200 nm) and high time-resolution (similar to 9 fs) was performed by the non-collinear optical parametric amplifier (NOPA). The relaxation time and the amplitude of the transient transmissivity changes (Delta T/T) are wavelength-dependent. The maximum Delta T/T appears at around 625 nm (similar to 1.98 eV) which corresponds to the transition between the Fermi level and the UHB (upper Hubbard band). Furthermore, the oscillations with similar to 150, similar to 320, similar to 500 cm(-1) have been clearly observed in the Fourier transformed graph of the 2D ultrafast spectroscopy, which are consistent with the phonon modes in Raman-scattering spectra.
Ultrafast Dynamics in Optimally Doped YBa2Cu3O7-delta Observed with White Light Pump-probe Spectroscopy
(2011-01-01)
Wang, Y. T.
;
Lee, Y. H.
;
Chen, Y. -J.
;
Tang, W. T.
;
Luo, C. W.
The quasiparticle relaxation dynamics in optimally doped (001) YBa2Cu3O7-delta thin films were measured at various temperatures by white light pump-probe technique. The 2D ultrafast spectroscopy with broadband (similar to 200 nm) and high time-resolution (similar to 9 fs) was performed by the non-collinear optical parametric amplifier (NOPA). The relaxation time and the amplitude of the transient transmissivity changes (Delta T/T) are wavelength-dependent. The maximum Delta T/T appears at around 625 nm (similar to 1.98 eV) which corresponds to the transition between the Fermi level and the UHB (upper Hubbard band). Furthermore, the oscillations with similar to 150, similar to 320, similar to 500 cm(-1) have been clearly observed in the Fourier transformed graph of the 2D ultrafast spectroscopy, which are consistent with the phonon modes in Raman-scattering spectra.