Second harmonic generation under two-photon resonance conditions

A study is made of the influence of two-photon resonance on phase matching in the case of doubling of the fundamental radiation frequency. It is found that maximum conversion is achieved either for a specific pump pulse duration or with preliminary wave mismatch of the interacting waves. An experiment on second harmonic generation in tellurium gives results which agree qualitatively with the theoretical predictions. An estimate is made of the real and imaginary parts of the third-order nonlinear susceptibility for tellurium.