Laser-induced gratings and wave mixing in large-gap semiconductors

There are numerous optical nonlinearities that may lead to the creation of laser-induced gratings and to four-wave mixing in the vicinity of the band edge. In direct, large-gap semiconductors some of the most dominant processes are a density-dependent (collision) broadening of the excitonic resonances, two-polariton transitions to the excitonic molecule, and the formation of an electron–hole plasma. The appearance of the diffracted beams is described both in the wave and in the quasi-particle picture. The relation is sketched between four-wave mixing and other scattering experiments, such as two-photon Raman scattering. The efficiency of the laser-induced gratings is studied as a function of the photon energies and the intensities of the two interfering beams as well as the temporal evolution of transmitted and diffracted beams.