Broadband (1.7–6.0 μm) multiline CO laser system with intra- and extracavity sum frequency generation in BaGa2GeSe6 crystals

•Slab RF discharge Q-switched multiline CO laser with intracavity frequency conversion.•BGGSe crystal operating both intracavity frequency converter and output coupler.•Optimized mode of slab RF discharge Q-switched multiline CO laser.•Second and third harmonic generation of CO laser. Broadband sum frequency conversion of a slab RF discharge Q-switched CO laser system was performed with two BaGa2GeSe6 crystals resulting in its spectrum lying within 1.7–6.0 μm spectral range. The first BaGa2GeSe6 crystal was located in the CO laser cavity and operated as both CO laser sum frequency (second harmonic) generator and laser output coupler. Another BaGa2GeSe6 crystal was applied for external third harmonic generation, i.e. as sum frequency generator for fundamental CO laser radiation and its sum frequencies obtained within the cavity. Peak powers of fundamental CO laser radiation, its second and third harmonics were up to 4.7 kW, 100 W and 0.5 W, respectively.