Generation of the difference frequency of two CO2 lasers in a ZnSe crystal

Tunable far-infrared (2–50 cm^–1) radiation was generated by optical mixing of radiations from two CO₂ lasers in a ZnSe crystal. The power of this far-infrared radiation was ~0.1 W when the power supplied by the lasers was ~2×10⁵ W. An estimate of the nonlinear susceptibility of the ZnSe crystal was obtained for this mixing process.