Enhanced output power for phase-matched second-harmonic generation at 10.6 μm in a ZnGeP_2 crystal

Second-harmonic generation was phase-matched at the fundamental wavelength of 10.6 mum in an annealed ZnGeP(2) crystal at room temperature. Our results demonstrated that the phase-matching angle was decreased with increasing the pump power. Such a unique dependence resulted in a significant enhancement on the second-harmonic output power. The highest average output power at 5.3 mum was 55 mW for an average pump power of 5.0 W, which corresponded to a conversion efficiency of 1.1%. Due to the laser-induced heating effect, the second-harmonic output power was increased by 65%. Such an efficient conversion was made possible also by using a short-pulse repetition-frequency-excited waveguide and single-longitudinal-mode CO(2) laser as a fundamental beam.