Abstract

Dispersions of the third-order nonlinear optical susceptibility of organic systems were measured in the optical region using a pump-probe method. With intense Nd:YAG laser pulses (30 ps) as the pump (ω₁), tunable cw dye laser radiation (ω₂) was used to probe the nonlinear medium for the third-order process ω₁ + ω₂ − ω₁ = ω₂. Use of a cw probe provides referenced measurements by accounting for temporal power fluctuations in the pump beam. All beams are unfocused allowing for direct comparison of experimental data to self-focusing theory. The dispersion of the third-order electronic response can be calculated using third-order perturbation theory with respect to the zero field wave functions. We use nitrobenzene as a representative system and analyze the dispersion in terms of the frequency-dependent contributions to the third-order susceptibility due to electronic excitations, molecular reorientation, and cascading processes.

© 1985 Optical Society of America