Collinear cascaded mid-IR frequency conversion in a single nonlinear optical crystal was accomplished. Concurrent collinear generation of the sum frequency of multiline fundamental band carbon monoxide laser radiation as a first frequency conversion cascade resulted in collinear difference frequency generation within the 4.3 to 4.9 μm spectral range when mixing this sum frequency radiation with the fundamental one as the second cascade in the same ZnGeP(2) nonlinear optical crystal.

Frequency doubling of mode-locked frequencytunable 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. Internal efficiency of SHG in ZnGeP2 crystal versus pump energy when the nonlinear crystal after focal plate. CO Laser transition 9→8 P(10) (λ ≈ 5.274 μm)

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