Dispersion of the second-order nonlinear susceptibility in ZnTe, ZnSe, and ZnS

We have measured the absolute values of the second-harmonic generation (SHG) coefficient |d| for the zinc-blende II-VI semiconductors ZnTe, ZnSe, and ZnS at room temperature. The investigated spectral region of the fundamental radiation ${\lambda }_F$ ranges from 520 to 1321 nm using various pulsed laser sources. In the transparent region of the II-VI semiconductors, the SHG coefficient exceeds the values of birefringent materials as ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP) by one or two orders of magnitudes. Above the $E_0$ band gap a strong dispersion of |d| is observed, showing a maximum for a second-harmonic frequency close to the $E_1$ gap. The experimental results are compared to calculated values using a simple three-band model including spin-orbit splitting. Substantial agreement is found to the experimentally observed dispersion of the second-order nonlinear susceptibility.