Cascaded second-harmonic and sum-frequency generation of a CO_2 laser by use of a single quasi-phase-matched GaAs crystal

Abstract
Cascaded second-harmonic and sum-frequency generation were used to obtain the third harmonic of a CO2 laser in a single quasi-phase-matched GaAs crystal. Both continuous-wave and pulsed regimes with a single-pass configuration were studied. The continuous case confirmed the good capability of the GaAs stack to bear high average power density. In the pulsed regime a 0.66% peak power conversion efficiency was achieved for the third harmonic when the laser was pumping at 8.2 MW/cm2, in fair agreement with theoretical predictions.