Fourth-harmonic generation of the CO2 laser wavelength at 10.5910 μm in BaGa4S7

This paper reports the 90° phase-matched fourth-harmonic generation of the CO2 laser wavelength at 10.5910 μm in BaGa4S7. The 1.4 cm long BaGa4S7 crystal used in the present experiment was cut at θ=9.2° in the xz(=bc) plane. The pump source was the second harmonic of the wave-guide CO2 laser (10.5910 μm) operating with an average output power of 18.3 W at 130 kHz. By focusing the 7.6 W, 5.2955 μm pulses (peak power is 6kW with 10 ns pulse duration) generated from the 2 cm long AgGa0.65In0.35Se2 crystal into the BaGa4S7 crystal (θPM=9.9°) with the 6 cm focal length ZnSe lens, the maximum average output power of 0.3 W was obtained at 2.6478 μm without any damage to the crystal. In addition, the new Sellmeier equations of BaGa4S7 are presented.