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For the first time, to the best of our knowledge, a broadband two-stage frequency conversion of multiline CO laser radiation was theoretically and experimentally demonstrated in a single AgGaSe₂ crystal. The first stage is sum frequency generation of CO laser radiation. The second stage is concurrent difference frequency generation within 4.3-4.9 μm spectral range when mixing sum frequency radiation with the pump radiation in the same AgGaSe₂ crystal. Internal sum frequency generation efficiency of multiline CO laser was up to 1%, while internal difference frequency generation efficiency was up to 0.065%.

Frequency conversion of CO laser radiation was experimentally studied in ZnGeP(2) and GaSe nonlinear crystals. To enhance conversion efficiency, we applied a CO laser system "master oscillator power amplifier" with concurrent mode locking and Q switching. The laser system emitted ∼1-μs train of ns pulses. Internal efficiency of frequency doubling reached 37% in ZnGeP(2) crystal and 5% in GaSe crystal. Two-stage frequency conversion (including second-harmonic and difference-frequency generation) in ZnGeP(2) crystal under optical pumping by a selective two-spectral line CO laser was studied.

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