Theory and analysis of excitation-probe studies of induced-absorption three-level molecular systems

The theory of dual-beam excitation-probe measurements for induced absorption three-level systems is presented, including third-order and fifth-order (excited-state absorption saturation) responses, molecular reorientational effects, and optical coherence effects. Negative coherent artifacts are predicted for the self-diffraction configurations and verified experimentally for the induced-absorptive dye 1, 3, 3, 1', 3', 3'-hexamethylindotricarbocyanine iodide. We obtain the reorientational times and the recombination lifetimes of the first and the second excited states of the material. These lifetimes are important to the design and exploitation of induced absorbers for optical limiting. The ratio between off-diagonal and diagonal ?⁽³⁾ tensor elements is also obtained from the modeling. © 1997 Optical Society of America.