Spectrum of two-photon interband absorption of laser radiation in semiconducting GaAs

An experimental investigation was made of the two-photon absorption in GaAs using laser radiation of 2$\hbar\omega$ = 1.50, 1.75, 1.89, and 2.34 eV energies at room temperature (the for jidden band width of the semiconductor was $\Delta$ = 1.43 eV). An anomalous rise in the absorption was observed at the band edge and this was interpreted theoretically as the influence of a deep impurity level in the middle of the forbidden band.