Analysis of the performance of a thermal defocusing optical limiter in the transient regime

A theoretical analysis of the performance of a thermal defocusing optical limiter in the transient regime-i.e., when the laser pulse duration is comparable to the acoustic transit time which governs the limiter response-is presented. First, an expression is obtained for the time- and space-dependent refractive index changes induced by a laser pulse in an absorbing liquid. This is used to calculate the nonlinear phase change experienced by the laser pulse while traversing the absorbing medium and then the transmission of the optical limiter. Results on the dependence of the optical limiter's performance on laser pulse duration are presented in a general form and also by considering a specific example.