<title>Optical power limiting in solutions of polyphenylquinoxalines</title>

Abstract

Two-photon absorption, excited state absorption, nonlinear refraction and scattering are the processes explored for optical power limiting applications. We report a novel approach for power limiting in polyphenylquinoxalines (PPQ) solutions based on two-photon induced cluster formation. The samples of PPQ were measured in solution in chloroform. The solutions are completely transparent at 532 nm. The contributions of the real and imaginary parts of the susceptibility were studied using the Z-scan technique. The nonlinear index of refraction of the samples is found to be positive. Open aperture Z-scan experiments indicate two photon absorption induced cluster formation and scattering. Values for the effective nonlinear absorption coefficient and the nonlinear index of refraction were obtained. Though two-photon absorption is responsible for triggering the process of cluster formation, optical power limiting in this case is due both to two-photon absorption and to scattering of light by the molecular clusters. The process of two- photon absorption and induced scattering yield a very attractive figure of merit of 10.3 for a solution sample of 2 mg/ml concentration compared to values reported in the recent literature. PPQ is an interesting candidate for applications in optical power limiting.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.