6-WAVE MIXING PROBE OF LIGHT-INDUCED 2ND-HARMONIC GENERATION - EXAMPLE OF DYE SOLUTIONS

Using a phase-conjugation configuration based on six-wave mixing interactions, we have investigated in detail the mechanism of photoinduced second-harmonic generation (SHG) in initially centrosymmetric materials. After some theoretical study of the process we discuss how different complementary tests (with the same experimental setup), such as investigations of the polarization properties or the lifetime dependence of the induced chi((2)) grating on the solvent, can reveal the microscopic characteristics of the process. We present experimental studies performed in various solutions of an ate-dye molecule (Disperse Red 1) with the 532-nm harmonic light along with the 1.064-mu m light from a picosecond-pulsed Nd:YAG laser. The results show good agreement with the theoretical predictions. It is shown moreover that the light-induced chi((2)) grating is due to oriental hole burning of the molecules, whereas reorientation of the molecules in the solvent is one major cause of relaxation.