COMPARISON BETWEEN THE OPTICAL LIMITING BEHAVIOR OF CHLOROALUMINUM PHTHALOCYANINE AND A CYANINE DYE

The picosecond optical limiting characteristics of the optical limitin g hexamethylindotricarbocyanine iodide (HITCI) and chloroaluminum phth alocyanine (CAP) compared and contrasted at 532 nm. From single pulse transmittance experiments, HITCI is shown to possess a serious limitat ion in its optical limiting behavior, where the regime of induced abso rption becomes one of induced transmission for high irradiances. CAP, on the other hand, although possessing a smaller ratio of the excited- state to ground-state absorption cross-section, continues to exhibit o ptical limiting over a much broader dynamic range. From cross-polarize d time-resolved excitation-probe measurements, HITCI exhibits a sharp negative spike around zero delay which originates from orientational c oherent grating effects, while CAP does not exhibit any spike. These n onlinearities are explained theoretically as a complex interplay betwe en a series of excited manifolds for the dyes and the radiation proper ties of the interacting laser pulse. (C) 1997 American Institute of Ph ysics.