Toshiaki Hattori

The application of incoherent light for the study of femtosecond-picosecond relaxation in condensed phase

A convenient technique for the ultrashort-relaxation-time measurement using temporally incoherent light instead of short pulses can be applied to the studies of relaxation processes. Theoretical studies on measuring various types of relaxation times by this method are summarized. We have applied this technique to the studies of the electronic dephasing in a polydiacetylene film, the vibrational dephasing in dimethylsulfoxide and the relaxation of optical Kerr effect in CS2 and nitrobenzene.

Ultrafast optical Kerr dynamics studied with incoherent light

Femtosecond optical Kerr dynamics in various transparent liquids were measured using incoherent light with a 60 fs autocorrelation width. From the measurement of the optical Kerr effect (OKE) of binary mixtures of CS2 and various liquids, the contribution of the intermolecular interaction‐induced polarizability change to the OKE was found to be affected remarkably by the femtosecond molecular dynamics of CS2. Especially, data from diluted solutions of CS2 in nonviscous solvents composed of molecules with a low molecular weight are consistent with the binary collision model in free space. An oscillatory feature, which was attributed to an intermolecular vibrational mode, was found in the OKE dynamics of neat benzene and several benzene derivatives. A theoretical expression for the delay‐time dependence of the signal intensity was also derived with no restriction on the statistical properties of the incoherent light. It is expressed in terms of the autocorrelation function of the intensity fluctuation of th...

Femtosecond dephasing in a polydiacetylene film measured by degenerate four-wave mixing with an incoherent nanosecond laser

Abstract Dephasing times in a polydiacetylene (poly-3BCMU) film were resolved for the first time at two wavelengths by degenerate four-wave mixing using incoherent light. The dephasing times, 30 fs at 648 nm and 130 fs at 582 nm, correspond to excitons in chains of the polymer with different conjugation lengths.

Measurement of dephasing time using incoherent light in the Kerr shutter configuration

We propose a convenient signal-selective method to measure the dephasing time using incoherent light performed in the Kerr shutter configuration. The advantage of this method is easy alignment, which allows one to obtain a better signal-to-noise ratio than with ordinary forward two-beam degenerate four-wave mixing. The dephasing time of Cresyl Violet doped in a polymethyl methacrylate film obtained by this method is compared with the result from ordinary two-beam degenerate four-wave mixing.

Femtosecond dephasing in a polydiacetylene film observed by degenerate four-wave mixing with an incoherent nanosecond laser

Abstract There has been much interest in the dynamical properties of excited states in polydiacetylenes (PDAs). The dephasing time (T2) in PDAs has been studied by several groups, but not resolved yet. We could for the first time measure the dephasing time in PDA (poly-3BCMU) by degenerate four-wave mixing (DFWM) using a temporally incoherent nanosecond laser with a correlation time as short as about 100 fs at the wavelengths of 648 nm or 582 nm. DFWM signals diffracted in two directions were detected simultaneously, and with the observed peak separations, dephasing times are calculated to be 30 fs at 648 nm and 130 fs at 582 nm with a simple two-level model. From these results, it was concluded that the exciton dephasing takes place more rapidly in the rod-like form of poly-3BCMU than in the coil-like form with a shorter conjugation length.

Femtosecond Studies of Dephasing and Phase Conjugation With Incoherent Light

The fast response of electroactive polymers as nonlinear optical materials is one of the main features which are attracting attention of increasing number of researchers. Especially, the large optical nonlinearity of organic polymeric systems containing conjugated π-electron structures is expected to have response times in femtosecond regime because of their purely electronic origins. Some of them are regarded as attractive candidates for ultrafast optical processing devices, and a switching time of 0.1 ps is suggested for an optical switch utilizing a polydiacetylene as a nonlinear material.1 Studies of the fast response of optical nonlinearity are most simply performed by transient four-wave mixing, and optical nonlinearities of several organic materials have been studied by transient four-wave mixing using short optical pulses.2–6 In this article, we describe femtosecond and picosecond measurements of relaxation times of optical nonlinearity by three types of four-wave mixing using temporally incoherent light instead of short pulses.

Incoherent Light Application To The Measurement Of Vibrational And Electronic Dephasing Time

The convenient method for the short-time measurements using temporally incoherent light instead of short pulses was applied to electronic- and vibrational-dephasing-time measurement. Electronic dephasing in a polydiacetylene film and vibrational dephasing in dimethylsulfoxide liquid were observed with femtosecond time resolution.

Vibrational and Electronic Dephasing Time Measurement with the Use of Temporally Incoherent Light

The dynamical properties of matter have been studied by increasing number of scientists, and information with higher time resolution is being obtained by the development of picosecond and femtosecond spectroscopies. Since picosecond light pulses were first emitted from passively mode-locked ruby laser in 1965 [1], continuous efforts to get shorter pulses have been made, and recently optical pulses as short as 8 fs were obtained [2] by the method of pulse compression of the output from a group-velocity-dispersion-compensated colliding-pulse mode-locked laser. Time-resolved coherent and conventional spectroscopies have been applied to several systems using ultrashort light pulses with pulse width of a few tens to a hundred femtoseconds. However, there are several difficulties in the study of the ultrafast phenomena using such short pulses: (i) Laser systems for the generation of ultrashort pulses are necessarily very expensive and complicated. (ii) The wavelengths of femtosecond laser pulses are limited in the region around 615–625 nm because of the lack of appropriate combination of saturable absorber and gain medium, and the tunability of each laser is generally poor. (iii) It is difficult to maintain a short pulse width in actual optical systems, since shorter pulse has broader power spectrum and suffers from dispersion broadening when it passes through ordinary dispersive or nonlinear materials.