Abstract

Four-wave mixing spectroscopic methods such as the transient grating (TG) method have been widely applied to the study of photophysical and photochemical processes in the condensed phase. Conventional TG measurements are usually performed in a homodyne manner and the signal is proportional to the modulus sqaured of the third-order polarization P⁽³⁾. The dynamic time constants were usually extracted by doubling the fitting results [1], which assumes that the real and imaginary components follow the same dynamics. In this work, we carried out heterodyne detection of the TG signals with a simplified diffractive optics method to measure the real and imaginary components of P⁽³⁾ separately. Our results show that the above assumption is true in the simple two-level system, while very different real and imaginary response were observed for a multi-level system.

© 2002 Optical Society of America