Optical limiting in solutions of diphenyl polyenes

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Abstract
The optical-limiting behavior of a series of trans-α, ω-diphenyl polyene compounds was observed in solutions of chloroform. The influence of planarity, the substitution of donor and acceptor groups, and the extent of π-electron delocalization on the nonlinear thresholds of the diphenyl polyenes in an optical-limiting geometry were examined. A saturation effect of optical-limiting nonlinear thresholds, consistent with the theoretical work, was observed at 10–11 π-electron bonds. The temporal profiles of the transmitted laser pulses and the power dependence of the nonlinear thresholds as a function of spot size and wavelength were examined. These examinations led to the conclusion that the predominant nonlinear mechanism was quasi-steady-state self-focusing. Nonlinear thresholds an order of magnitude lower, and thus effective n2 and χ3 values an order of magnitude higher, than the well-known self-focusing medium CS2 were observed. Our studies demonstrate that this series of polyenes consists of efficient broadband nonresonant optical-limiting materials.