High-energy, high-beam-quality, and widely tunable nanosecond KTA OPO-OPA laser system.

Simultaneously achieving high pulse energy, high beam quality, and a wide tuning range remains a major challenge for nanosecond optical parametric systems. To avoid the beam quality degradation typically observed in single-stage OPOs under high-energy pumping, a cascaded optical parametric oscillator and amplifier (OPO-OPA) architecture with angle-tuning applied to both stages was adopted. For KTiOAsO4 (KTA) crystals cut at 41.6° in the XZ plane, a wide tuning range from 1528 to 1579 nm was enabled by rotating them approximately ±0.4°. A maximum signal pulse energy of 34.6 mJ was achieved at 1568 nm, with corresponding beam quality factors of Mx2 = 2.16 and My2 = 2.67. Furthermore, such high beam quality was maintained across the entire tuning range. This work provides an effective approach for generating laser pulses with high energy, high beam quality, and wide tunability.