28-W, 1.49-µm, 300-Hz ring-cavity OPO with critically phase-matched KTiOAsO ₄ enabled by walk-off compensation and transverse cavity-mode bias compensation via orthogonal walk-off directions

Walk-off compensation and transverse cavity-mode bias compensation are simultaneously implemented in a four-mirror ring-cavity optical parametric oscillator (OPO). Four 41.2°-cut KTiOAsO 4 (KTA) crystals are arranged into two walk-off-compensating pairs, and the two pairs are oriented in orthogonal walk-off directions, enabling effective intracavity exchange and averaging of the walk-off-induced transverse gain asymmetry. In addition, secondary energy extraction is implemented by reusing the residual pump. At 300 Hz, a 28.1-W output at 1.49 µm is obtained. With these combined measures, the spatial output characteristics of critically phase-matched OPOs affected by spatial walk-off are improved, and the parametric conversion efficiency is enhanced.