Two-photon spin generation and detection

Abstract

A time- and polarization-resolved two-photon pump-probe investigation is performed in lightly doped GaAs. We generate spin-polarized electrons in bulk GaAs at various temperatures using right-circularly polarized two-photon excitation and detect them by probing the spin-dependent transmission of the sample. The spin polarization (P) of conduction band electrons, as measured using probe pulses with the same (right) and opposite (left) circular polarization, is measured in dependences of pump-probe delay (?t), lattice temperature (TL), doping density (n) as well as of the excess photon energy ?E2? = planck2? - Eg, where Eg is the band gap energy. P is found to be decayed with ?t and enhanced with the decrease in TL or the increase in n. It is also found that P decreases with the increase in ?E2? and depolarizes rapidly for ?E2? > ?ESO, where ?ESO is the spin-orbit splitting energy. The results demonstrate that due to a much longer absorption depth highly polarized spins can be generated optically by two-photon pumping of bulk semiconductors.