Indirect two-photon transitions in Si at 1.06 m

We have studied the nonlinear optical absorption in silicon at 1.06 m using picosecond pulses. By measuring the time dependence of the induced absorption we are able to separate the effects of indirect simultaneous two-photon absorption and stepwise absorption processes. Values of the two-photon absorption coefficient at 1.06 m were measured to be 1.9 cm/GW (20 K) and 1.5 cm/GW (100 K). © 1973 The American Physical Society.