Optical Second-Harmonic Generation in ZnS—CdS and CdS—CdSe Alloys

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Abstract
Optical second‐harmonic generation has been measured as a function of alloy composition in wurtzite ZnS—CdS and CdS—CdSe monocrystals. The relative values of the nonlinear susceptibilities were determined; χ33 increased by nearly one order of magnitude as the band gap was decreased from 1.52(2h/ω) to 0.73 (2h/ω). (Because of this strong increase in χ33, appreciable second‐harmonic signals were detected in the crystals of the series which were highly absorbing at the harmonic frequency.) This agreed with the predictions of a quantum‐mechanical analysis. Studies of other II‐VI and III‐V compounds indicated a strong dependence of the second‐order susceptibilities upon the band gap.