Mode-locked CO laser frequency doubling in ZnGeP2 with 25% efficiency

Frequency doubling of mode-locked frequency-tunable CO laser emission in high quality 17-mm long ZnGeP2 nonlinear optical crystal was studied. The internal efficiency of frequency doubling exceeded 25%, which was obtained by stabilization of mode-locking regime and increasing peak power of pump radiation in the scheme ``master oscillator – power amplifier''. A feasibility of difference frequency conversion of both fundamental and first overtone CO laser lines to cover ~ 4.0 – 5.0 μm spectral range and a possibility of getting spectral range of ~ 1.25 – 10 μm by mixing of all CO laser lines were estimated.