Beam quality improvement of the high-energy KTA-OPO based on a confocal unstable cavity with Gaussian reflectivity mirror

A high-energy 100-Hz optical parametric oscillator(OPO)based on a confocal unstable resonator with a Gaussian reflectivity mirror was demonstrated.A KTA-based OPO with a good beam quality was obtained when the magnification factor was 1.5,corresponding to the maximum signal(1.53 pm)energy of 56 mJ and idler(3.47 pm)energy of 20 mJ,respectively.The beam quality factors(M2)were measured to be M2x=5.7,M2y=5.9 for signal and M2x=8.4,M2y=8.1 for idler accordingly.The experimental results indicated that the beam quality positively changed with the increase of magnification factors,accom-panied by an acceptable loss of pulse energy.