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A pulsed TEA CO2 laser was used in an investigation of the influence of the pump radiation parameters (mode composition, wavelength, pulse duration), of the focusing conditions, of the properties of the material (absorption coefficient), and of the operating conditions (temperature) on the efficiency of conversion to the second harmonic and on the angular dependences of phase matching in ZnGeP2 crystals. The calculated results were found to be in good agreement with the experimental data.

We have succeeded in generating the second harmonic of the radiation from a DF laser for the first time, using single crystals of ZnGeP2. For crystals with lengths of 10.1 and 13.6 mm, the overall external efficiencies of the entire oscillator system were 4 and 6.2%. The internal efficiencies of second-harmonic generation in the crystals were 7.6 and 11.8%, respectively.

The second harmonic of radiation from a molecular NH3 laser was generated for the first time in CdGeAs2 single crystals. The internal efficiency of the frequency doubling reached 5% for radiation at the wavelength of 11.7 μ, when the efficiency of conversion of CO2 laser radiation power (used for direct optical pumping of the NH3 laser) into 6-μ radiation was highest.

The frequencies of CO2 and CO lasers were summed in a ZnGeP2 crystal as a result of a type I three-frequency interaction: the phase-matching angle was θpm =56° and the angular width of the phase-matching curve was 2°50'. The output power of the sum-frequency radiation was ~0.6 mW.

The second harmonic of CO2 laser radiation was generated for the first time in ZnGeP2 single crystals under phase-matching conditions when the pump (fundamental-frequency) radiation was tuned within the ranges 9.19–9.7 and 10.15–10.8 μ. A study was made of the spectral, angular, and temperature widths of the phase-matching curve, of the dependence of the efficiency of conversion to the second harmonic on the pump wavelength and temperature of a crystal, and of the rate of reduction in the phase-matching angle as a result of heating.

Frequency conversion of nontraditional CO2 laser radiation bands was performed for the first time. The second harmonic of the 4.3μ (1001–1000) band was generated and this was summed with the second sequence band at 10.4μ (0002-1001). The phase matching angles were 55°50' and 54°20', respectively. The spectral and angular phase-matching bandwidths were investigated. The efficiency of doubling of the P(26) line in the 4.3μ band by conversion in a ZnGeP single crystal exceeded 10%.

A study was made of second-harmonic generation in a high-quality ZnGeP2 crystal (absorption coefficient 0.1 cm−1 ) . The second-harmonic power ranged from 2.45 to 4 mW when the CO laser power was 81.25–194 mW. The maximum external efficiency of second-harmonic generation reached 3%.

Efficient (49 ± 5%) second harmonic generation was demonstrated for the first time in the infrared. The frequency of CO2 laser radiation with a pulse duration of ~2 nsec and an intensity of up to 1GW/cm2 was doubled in an unbleached ZnGeP2 crystal. The internal energy efficiency was ~80%.

An experimental investigation was made of cascade generation of the fourth harmonic of CO2 laser radiation and of the second harmonic of CO laser radiation in single crystals of zinc germanium diphosphide. The radiation was converted to the spectral range 2.3–3.1 μ. The overall efficiency of conversion of CO2 laser radiation to the fourth harmonic was ~ 0.1 %, but it should be possible to increase it to 20%. The efficiency of conversion of CO laser radiation to the second harmonic was (2.5–10)×10−3%.