Difference-frequency generation in a GaAs crystal with a periodic domain structure in the field of a few-cycle laser pulse is considered for the case of weakly pronounced material dispersion. The straight-line method is used to solve numerically the system of coupled nonlinear partial differential equations describing the evolution of the electric field of this laser pulse in GaAs crystals with periodic and chirped domain structures. It is shown that application of a GaAs crystal with a chirped domain structure makes it possible to control the frequency-modulation law for a broadband differencefrequency pulse.
Photoacoustic (PA) measurements were carried out at 95 K for semi-insulating (SI) GaAs. A broad peak at 0.92 eV and humps in the higher-energy region are observed. Onsets of the humps are at 1.04 and 1.25 eV. Among these structures in the PA spectra, the broad peak at 0.92 eV is partly photoquenched upon illumination of a secondary light (hν=1.12 eV) and thermal recovery occurs after heating to around 150 K. The spatial profiles of this photoquenching along the wafer diameter show a W-shaped distribution. These results indicate that the quenching component of the peak at 0.92 eV in the PA spectra is due to nonradiative recombination of electrons excited from the EL2 level to the Γ-conduction band minimum. The electron transitions involving the EL2 level can be resolved by the PA measurements for the first time. Source:IOPscience