Frequency-Domain Nonlinear-Optical Measurement of Femtosecond Relaxation

Abstract

Femtosecond optical studies of molecular motion in liquids are providing new insight into the fundamental properties of the liquid state. The authors have developed a novel frequency-domain very-high-temporal-resolution nonlinear-optical technique for measuring femtosecond events and have employed it to study ultrafast processes in liquids. They measure the dispersion of the third-order nonlinear-optical susceptibility, chi /sub ijkl//sup (3)/( omega /sub 1/- omega /sub 2/+ omega /sub 3/) with omega /sub 1/- omega /sub 2/approximately=0. The frequency-dependence of the third-order susceptibility under this resonance condition is the Fourier transform of the material response. They have developed a three-laser frequency domain technique (nondegenerate four-wave mixing) that allows the measurement (with a resolution of ~1 fsec) of any optically induced femtosecond effect in any material phase. This technique provides high signal-to-noise ratio and background-free operation. Any element of the third-order susceptibility tensor can be studied, and much freedom in parameter choice is available