Quantum kinetic theory of two-beam current injection in bulk semiconductors

We develop a theory of current injection in bulk semiconductors by simultaneous excitation with two laser beams with frequencies $2{\omega }_0,$ ${\omega }_0.$ Coherent mixing of the resulting one- and two-photon transitions generates an effective field $A_{\mathrm{eff}}\left(\mathbf{k}\right)$ with different strengths at $\pm \mathbf{k}$ points in momentum space. This asymmetry in carrier generation, producing the induced current, is controlled by the relative phase of the two fields. Quantum kinetic equations for the photogenerated carriers are derived from nonequilibrium Green functions. They are simplified here to the Boltzmann limit, and applied to a model of GaAs in the presence of LO phonons. Different forms of the conduction electron distributions result for generation from light- and heavy-hole bands, and give different saturation and relaxation rates for the induced current. Generation of THz radiation by the current is also discussed.