Coherent control of charge currents, spin currents and carrier density in bulk gallium arsenide using non-degenerate transient grating techniques.

摘要

Coherent control processes are studied in bulk GaAs at room temperature using nondegenerate transient grating techniques. These processes occur due to the phase dependent quantum interference between one- and two-photon absorption pathways of two non-collinear 775 and 1550 nm optical beams. Due to the beams' propagation directions, quantum interference is spatially modulated resulting in the generation of different types of gratings. Depending on the beams' polarizations and sample orientation, a current-induced grating or a directly-induced carrier density grating is observed. The grating diffraction efficiency is measured as a function of time with 830 nm probe pulses.; The temporal evolution of a charge current-induced grating generated by p-polarized optical beams is investigated. The grating diffraction efficiency initially rises, as the pump pulses arrive, then decays in ∼ 400 fs to a non-zero value from which it rises again and peaks in ∼ 5 ps, followed again by a decay within ∼13 ps. A hydrodynamic model is developed to explain the temporal behavior of this grating. Evolution of the charge current grating to the carrier density and temperature grating and its subsequent decay in time are described. The role of different carrier kinetics such as carrier cooling, inter-valley scattering and ambipolar diffusion in the temporal evolution of current-induced grating are also investigated. The use of the hydrodynamic model to describe the experimental results indicates an injection of carriers with a net quasi-particle momentum during the grating generation.; Generation of a spin current grating by cross-linearly polarized optical beams and its evolution to a spin density grating is also demonstrated. The grating diffraction efficiency initially rises with the pump pulses, followed by a decay within ∼3 ps, attributed to electron diffusion.; Carrier density gratings are also generated directly by the quantum interference between the optical beams. For beams' polarizations and crystal orientations that permit both directly-induced density grating and charge current-induced density grating to form, interference is observed between the two types of gratings which have approximately the same amplitude despite the different processes need to form them. This interference is investigated by measuring the diffraction efficiency as a function of sample orientation.