Self-defocusing and self-phase modulation in InSb measured with picosecond infrared pulses

The nonlinear distortion of the beam profile by self-defocusing is studied at the absorption edge of InSb with tunable picosecond pulses. In addition, the rapid change of the refractive index Δn is monitored by self-phase modulation of the infrared pulses. A quantitative analysis of the results gives a Δn≂4×10−2 at a pulse energy of 10−6 J. The optical nonlinearity occurs on a time scale shorter than 4 ps.