Nanofabrication of Lithium Niobate Anti-Reflective Subwavelength Structures for High Power Mid-Infrared Lasers

Lithium niobate (LN) crystal with anti-reflective subwavelength structures (ASSs) has great applications in high-power tunable optical parametric oscillator (OPO) lasers. However, it is still a great challenge to 3D nanofabrication of LN ASSs. Herein, a wet-etching-assisted laser polarization domain inversion (WE-LPDI) technology is proposed to fabricate periodic cone arrays with a period from 200 nm to 4 µm on LN. Based on the optimized structural parameters, large-area LN ASSs with a period of 1.3 µm and a height of 1.7 µm were fabricated on LN, which exhibits an average transmittance of 3–5 µm increasing from 78% to 85% and a highest transmittance of 88% at 5 µm. It has been demonstrated that the LN ASSs show high stability under high-temperature and high-power laser irradiation, which shows potential applications for high-power mid-IR lasers. The results indicate that the WE-LPDI technology provides a novel way for 3D nanofabrication of LN.