Investigation of transient nonlinear optical mechanisms using a variable pulselength laser

We show a variable pulselength laser to be extremely useful when investigating the dynamics and parameters of optomechanical nonlinarities in optical materials. Pulselength variability allows observation of the transient nonlinear behavior using nanosecond pulses and determination of the underlying physical mechanisms using subnanosecond pulses. It also enables observation of the transition response between the two time regimes where intrinsic polarizabilities compete with optomechanical effects. We examine the transient nonlinear scattering properties of an optical power limiter, platinum ethynyl, and compare it to carbon disulfide using degenerate four-wave mixing. Intensity, polarization, and pulselength control allow us to measure acoustic scattering and decay parameters, /spl chi//sup (3)/ magnitudes, and the transient laser-induced grating behavior.