Linear and nonlinear optical properties of AgGaS2, CuGaS2, and CuInS2, and theory of the wedge technique for the measurement of nonlinear coefficients

The refractive indices of the ternary semiconductors AgGaS2, CuGaS2, and CuInS2have been measured over the entire range of transparency of these crystals. The optical nonlinear coefficients for second-harmonic generation have also been determined. Three-frequency collinear phase matching is analyzed in detail for AgGaS2. The birefringences of CuGaS2and CuInS2are not large enough to permit three-frequency phase matching within the transparent regions. A parametric oscillator threshold calculation for a pump wavelength 0.89 μ, which is within the range of the GaAs injection laser, indicates that AgGaS2is promising for this application. The upconversion efficiency in AgGaS2for sum mixing of the CO2laser ( ) with the xenon ion laser ( ) is also calculated. The result indicates that, depending upon system requirements and the availability of high optical quality material, AgGaS2can be comparable to ZnGeP2for upconversion. In Appendix II, we present a theory of the wedge technique for the measurement of nonlinear coefficients. This theory takes into account losses and assumes a Gaussian beam geometry. Furthermore, a discussion of units in nonlinear optics is given.