Time-resolved specular inverse faraday effect: direct measurement of carrier spin relaxation times and optical nonlinearities in opaque solids

Abstract

The Specular Inverse Faraday Effect (SIFE) is the nonlinear optical effect of stimulation of a medium with a strong circularly polarized pump wave, resulting in alteration of the polarization state of a liearly polarized probe wave reflected from the medium’s surface (see inset in Fig. 1). This effect has been recently demonstrated but not temporally resolved with picosecond optical pulses in various solids, including semiconductor,’.‘ diluted magnetic semiconductor: and superconducting materials4 There is no obvious limitation (except the laser pulse duration) on the time resolution of the method in the study of transient effects. Here we report on first observation of transient incoherent and coherent SIFE. In incoherent SIFE, the probe polarisation azimuth rotation in reflected light is dependent on the pump-induced difference of absorption coefficients for right and left circularly polarized light. This difference appears because of the transfer of the pump-light pulse momentum to the sample. Incoherent SIFE is directly spin-polarization sensitive. Coherent SIFE is a result of a degenerate four-wave mixing process on cubic nonlinearity in the skin layer of the crystal. It depends on the phase difference between the pump and the probe waves. Observation of the transient coherent and incoherent SIFE was performed with a bulk sample of good substrate quality GaAs crystal at room temperature. The light source used was a mode-locked Ti: sapphire laser pumped by an argon-ion laser. It produced T~ = 2 ps pulses at the wavelength A = 750 nm. GaAs is completely opaque at this wavelength with ... & more.