By measuring, as a function of temperature, the nonlinear light transmittance from neodymium and ruby lasers, the ZnTe two-photon absorption (TPA) has been studied both near the direct band gap and close to the critical point E₁. The TPA absolute coefficients have been determined by means of the two-channel normalization technique. It has been found that for 2ω≥Eg, the TPA spectrum line shape has a dependence that is peculiar to absorption involving exciton levels, while for 2ω close to E₁, the line shape has a (2ω-Eg)3/2 dependence, which is typical of the "allowed-forbidden" mechanisms corresponding to the two-band model. By comparing the TPA experimental and theoretical values, it has been found that the TPA is strongly influenced both by the exciton effect and by the valence-band degeneracy.
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Catalano et al. (1979) studied this question.
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