Selective bond breaking of ethanol in intense laser fields

Itakura, Ryuji; Yamanouchi, Kaoru*; Yazawa, Hiroki*; Shioyama, Tadamasa*; Kannari, Fumihiko*

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.