Ultrafast optical imaging of the spin Hall effect of light in semiconductors

We experimentally demonstrate a general optical pump-probe technique to observe the spin Hall effect of light SHEL in an absorbing medium. In essence, a locally confined pump-induced modification of a material’s absorptivity can effectively be used as an induced aperture allowing one to detect the transversely displaced circular polarization components of an incident beam through differential transmission techniques. We consider linear absorption mechanisms such as free-carrier absorption and Pauli blocking as well as nonlinear absorption processes such as two-photon absorption. For absorption mechanisms that do not depend on light polarization, the SHEL of the probe beam is obtained directly, while polarization-dependent properties give an effective SHEL displacement that depends on the action of the SHEL on both pump and probe beams. Using 150 fs pump, 820 nm pump and probe pulses we observe SHEL effects in silicon via free-carrier absorption. SHEL effects are also observed via Pauli blocking at 820 nm and two-photon absorption at 1550 nm in GaAs using 150 fs pump and probe pulses.