Spin resonant optical mixing in InSb — CW-measurements and transient effects

Optical four-wave mixing due to the resonant spin nonlinearity in n-InSb was observed in magnetic fields up to 1.4 T. The mixing of two CO-laser frequencies ω₁ and ω₂ = ω₁ - Δω yields radiation with frequencies ω₁ + 2Δω, ω₁ + Δω, ω₁ - 2Δω, and ω₁ - 3Δω. We found the resonant contribution to the third order nonlinear susceptibility arising from the spin-flip interaction to increase by more than two orders of magnitude when ω₁ is varied from 1760 cm^-1 to 1896 cm^-1. With the lasers working simultaneously Q-switched we observed radiation at ω₁ + Δω and ω₁ - 2Δω due to the mixing caused by the nonparabolicity of the conduction electrons even without an external magnetic field. At the resonant magnetic field the intensity of the mixed radiation is increased by more than one order of magnitude and is also observed when the laser pulses do not hit the sample simultaneously as long as the time difference between the two pulses does not exceed 450 ns. This points to a spin dephasing time T₂ of about 100 ns.