Fundamental aspects of light scattering and optical Kerr effect spectroscopy

Abstract

We describe the principles of two spectroscopic methods of non-resonance light scattering (LS) and optical-Kerr-effect (OKE) spectroscopies in detail, and review basic but truly important phenomena observed by these two methods. Particularly, we focus on the following three experiments: 1) Response functions determined by frequency-domain LS and time-domain OKE spectroscopies, almost completely agree with each other, indicating that the quantum-mechanical fluctuation-dissipation theorem (QM-FDT) holds well in this system. 2) Femtosecond time responses of liquids clearly show an initial rise process even though they show an exponential response at a later time. This indicates that the Debye relaxation model does not hold in such an early time region. 3) From the measurement of the Stokes and anti-Stokes LS intensity ratios, it is found that the LS spectra of relaxation modes in liquids and solids are symmetric with respect to the spectral origin of the scattered light and hence the ratio does not satisfy the Boltzmann distribution rule expected from QM-FDT. These experimental results which contain apparently contradictory data are closely related with the nature of relaxation modes examined, which more or less assume a macroscopic character, and also with the physical basis of relaxation, which is inevitably connected to the observation problem of quantum mechanics. We discuss these points in relation to the physical reality of macroscopic quantity.