Laser-induced damage threshold comparison of untreated, antireflection-coated and antireflection-microstructured LiGaS 2 nonlinear crystals

Abstract LiGaS 2 crystals are prospective media for optical parametric oscillators. In such systems efficiency and maximum power output are often limited by the laser-induced damage threshold (LIDT) of nonlinear crystals. In addition, most nonlinear crystals have a high refractive index and consequently large Fresnel losses, thus encouraging the use of antireflection coatings. However, antireflection coatings are known to compromise the LIDT. This work presents results of the LIDT testing of LiGaS 2 nonlinear crystals in untreated, antireflection-coated and antireflection-microstructured variations. The tests were performed using a one-on-one method with pulsed lasers operating at 1.57, 2.09 and 2.5 μm wavelengths with pulse durations of 9, 149 and 12 ns, respectively. The paper covers damage site feature investigation and LIDT comparison of antireflection coating and antireflection microstructures. The key finding of the work is that antireflection microstructures can provide an increase in transmittance for both the pump and the signal, while maintaining a high LIDT.