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H
OH
on a light-dressed potential energy surface by ultrashort pump-and-probe laser pulsesYazawa, Hiroki*; Shioyama, Tadamasa*; Hashimoto, Hiroshi*; Kannari, Fumihiko*; Itakura, Ryuji; Yamanouchi, Kaoru*
Applied Physics B, 98(2-3), p.275 - 282, 2010/02
Times Cited Count：5 Percentile：28.67(Optics)We experimentally investigate the dynamics of vibrational wave packets on the light-dressed-potential energy surface (LD-PES) of CHOH using a pump-and-probe pulse excitation scheme. The probability of non-adiabatic transition at 800 nm from the singly ionized ground state to the repulsive excited state leading to C-O bond breaking is enhanced when a probe laser pulse is delayed by around 180 fs. At this pulse delay, on the other hand, C-C bond breaking is significantly suppressed. Therefore, the deformation of LDPES is considered to change the direction of the wave packet traveling originally along the C-C stretching into the direction along the C-O stretching. This non-adiabatic transition leading to the redirection of the dissociating wave packet is found to occur more efficiently at the probe laser wavelengths at 400 nm than at 800 nm. The critical pulse delay is still around 180 fs even at 400 nm.
Yazawa, Hiroki*; Shioyama, Tadamasa*; Suda, Yoshitaka*; Yamanaka, Mio*; Kannari, Fumihiko*; Itakura, Ryuji; Yamanouchi, Kaoru*
Journal of Chemical Physics, 127(12), p.124312_1 - 124312_5, 2007/09
Times Cited Count：10 Percentile：34.05(Chemistry, Physical)Ethanol molecules were irradiated with a pair of temporally overlapping ultrashort intense laser pulses (10
-10
W/cm
with different colors of 400 and 800 nm, and the dissociative ionization processes have been investigated. The yield ratio of the C-O bond breaking with respect to the C-C bond breaking was varied in the range of 0.17-0.53 sensitively depending on the delay time between the two laser pulses, and the absolute value of the yield of the C-O bond breaking was found to be increased largely when the Fourier-transform limited 800 nm laser pulse overlaps the stretched 400 nm laser pulse, demonstrating an advantage of the two-color intense laser fields in controlling chemical bond breaking processes.
Itakura, Ryuji; Yamanouchi, Kaoru*; Yazawa, Hiroki*; Shioyama, Tadamasa*; Kannari, Fumihiko*
no journal, ,
Recent progress in ultrashort pulsed laser technology has enabled us to control chemical reaction dynamics in intense laser fields. In this study, we investigate responses of ethanol to a train of intense laser pulses by changing systematically the parameters such as the number of pulses within a train and the chirp rate of respective pulses. It is confirmed that the most critical factor governing the bond breaking dynamics is an overall temporal width of laser pulses as far as laser pulses with the central wavelength of 800 nm and the spectral width of 26 nm are adopted. The smoothly connected pulses in a train to be a single long pulse (
1 ps FWHM) shows larger ratio of the C-O bond breaking than the pulse train with temporally isolated multiple pulses. However, when the temporal separation between the pulses becomes shorter than 100 fs, the branching ratio between the two bond breaking pathways shows no difference from that by a smoothly lengthened pulse. We also perform the adaptive pulse shaping in order to find an optimal solution for obtaining the maximum branching ratio. By the analysis of the optimized laser pulses, it is found that the temporal fine structure within a laser pulse appearing in the range less than 100 fs does not influence the branching ratio, and that the overall temporal duration of a laser pulse is a major factor in determining the branching ratio.
