Abstract
We report laser-induced transient grating experiments performed on a 4-μm-thick CdS platelet near its band edge at room temperature. With this technique the lifetime and the diffusion of the plasma, generating the optical nonlinearities, could be studied with a picosecond time resolution. The diffusion of the electrons and the holes constituting the generated plasma has been found to be ambipolar at low carrier densities. A diffusion constant D = 1.6 cm2/s and a lifetime T1 = 3 ns have been determined. Under high-excitation conditions the gratings show deviations from simple exponential decays for only their smaller spacings, when their smearing out is mainly governed by the diffusion. This behavior cannot be explained by higher recombination rates like radiative and Auger ones. To describe our experimental results, we consider a phenomenological model in which the diffusion is no longer ambipolar.
© 1991 Optical Society of America
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