A Study on Dynamics in Organic Crystals Using THz-Repetition-Rate-Controlled Femtosecond Spectroscopy

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The purpose of the present study is to develop a method for controlling quantum states in condensed matters using THz-repetition-rate optical pulses and to find suitable materials effectively controlled. Results of our study are summarized as follows.1. An approach for generation of an ultrabroad-band optical pulse (550 THz width) is proposed, which is based on mutual induced phase modulation of three synchronized femtosecond pulses in a short fiber. These pulses having equidistant carrier frequencies and constant carrier-phase differences are obtained from the fundamental, the second-harmonic and the second-harmonic-pulse pumped parametric waves. Computer analysis shows that chirp of the composite wave at the fiber output can be compensated for by a spatial phase modulator and a 1.76-cycle pulse is generated.2. We built up a optical pulse shaping system consisting of a femtosecond Ti : sapphire laser, a Fourier-transformation unit, a pair of gratings and a spatial phase modulator. 2.0 … More 6 THz-repetition-rate optical pulses were generated.3. Using a femtosecond time-resolved four-wave mixing spectroscopic system, we first determined the third-order optical susceptibilities of 1- (3-thienyl) -3- (4-chlorophenyl) propen-1-one crystal and solution. We also found that their optical nonlinearities respond within 80 fs.4. From a femtosecond time-resolved, optically-heterodyne detected optical Kerr measurement, it was found that carotenoid solutions have effectively negative third-order nonlinearities responding femtosecond optical pulses. And it was shown that these nonlinearities are due to a two-photon process.5. Picosecond time-resolved emission spectra of guanine (G), guanosine (GS) and guanosine 5'-monophosphate (GMP) were measured with a few picosecond time resolution in neutral-acidic aqueous solutions by use of a femtosecond UV pulse laser and a highly sensitive streak camera. It was found that each emission consists of a fast decaying and a slow decaying components which are from monomers and protonated cation molecules, respectively. Less