Diffraction efficiency and decay times of free-carrier gratings in silicon

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Abstract
A spatially periodic distribution of electron‐hole pairs has been produced in silicon crystals by excitation with a pulsed neodymium yttrium aluminum garnet (Nd: YAG) laser. The diffraction efficiency and the decay time of the grating structure has been measured by diffraction of an independent quasi‐cw laser beam as a function of the energy density of the exciting laser. At low energy‐densities the diffraction efficiency is given by a squared Bessel function dependent on the carrier density as expected from theory. At higher incident energy densities deviations occur which can be explained by free‐carrier absorption and intensity fluctuations across the beam. The grating decay time is determined by ambipolar diffusion and Auger recombination.