Modulation and compression of Nd: YAG laser pulses by self-tuning of a silicon cavity

A Nd: YAG laser pulse (20 ns halfwidth) passing a silicon crystal (0.5 mm thickness) produces refractive index changes by free carrier production. The polished crystal with parallel faces behaves therefore like a Fabry-Perot cavity with time dependent transmission. With an incident energy density of up to 300 mJ/cm² the cavity can be tuned over up to 5 resonances. The temporal shape of the transmitted pulse exhibits a corresponding number of maxima. Experimentally observed pulse shapes are compared with calculations. Deviations between theory and experiment at high energy densities are explained by increasing absorption due to the free-carriers. If the cavity is tuned over a single resonance a pulse compression can be achieved.