Efficient second harmonic generation in low-loss CdGeAs/sub 2/

Summary form only given. Cadmium germanium arsenide, CdGeAs/sub 2/, has long been sought after as the ultimate crystal for frequency-doubling the output of CO/sub 2/ lasers. It has an enormous nonlinear coefficient (d/sub 36/=236 pm/V, the highest among materials with an adequate transparency range), enough birefringence to allow phase matching (type I and type II), and sufficient thermal conductivity (0.04 W/cmK) for high average power operation. CdGeAs, has been limited, however, by defect-related absorption losses that peak in the mid-infrared in the wavelength range of the second harmonic. In order to achieve second harmonic generation (SHG), therefore, even the best crystals to date had to be cooled to 77 K in order to achieve output powers up to 2.25 W at a maximum conversion efficiency of /spl sim/27%. Here we report the result of recent loss reductions that allow comparable performance (28% conversion efficiency) near room temperature and a twofold improvement at 77 K.