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
A^{I}B^{III}C_{2}^{VI}
semiconductors AgGaS
2
, CuGaS
2
, and CuInS
2
have 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 AgGaS
2
. The birefringences of CuGaS
2
and CuInS
2
are 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 AgGaS
2
is promising for this application. The upconversion efficiency in AgGaS
2
for sum mixing of the CO
2
laser (
\lambda = 10.5 \mu
) with the xenon ion laser (
\lambda = 0.597 \mu
) is also calculated. The result indicates that, depending upon system requirements and the availability of high optical quality material, AgGaS
2
can be comparable to ZnGeP
2
for 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.