Efficient harmonic generation of CO2 laser radiation in thallium arsenic selenide

The material TAS is a ternary chalcogenide salt with space group symmetry R3m, transparent between 1.3 and 17μm. Its large nonlinear optic coefficient and high damage threshold make TAS a promising candidate for nonlinear frequency conversion processes throughout the infrared.1 Recently, large, good quality crystals of TAS have been grown, cut, polished, and coated for CO2 laser second harmonic conversion by Westinghouse Research Laboratory. At NRL, a 2.5-cm diam 6-cm long crystal was pumped by a Lumonics 822 H P CO2 laser operating on the 9-μm P(20) transition with energy of 350 mJ in a 100 ns FWHM pulse. In type I doubling conditions, we have observed up to 25% total energy conversion to the second harmonic at 1 J/cm2 with no apparent crystal damage. Additionally, in a second similar TAS crystal we have observed both type I and type II sum frequency generation to the third harmonic with an overall total energy conversion of 1.5%. Progress toward a TAS-based OPO in the 8-12-μm range is also reported. (12min)