OPTICAL NONLINEARITY IN A MODE-LOCKING DYE - OPTICAL LIMITING AND 4-WAVE-MIXING

We report the optical nonlinearity resonantly induced by picosecond la ser excitation in Kodak 9740 mode-locking dye. The observed nonlineari ty is due to the participation of high-lying singlet states. The speci fic processes studied are optical limiting and phase conjugation. We i nfer that the mechanism underlying the limiting behaviour is due to tw o-photon absorption, and obtain a value for the two-photon absorption coefficient P. Further, we report the intensity dependence of the phas e conjugate signal and obtain the corresponding third-order susceptibi lity.