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. A wet‐etching‐assisted laser polarization domain inversion (WE‐LPDI) technology is proposed for the fabrication of LiNbO3 anti‐reflective subwavelength structures (ASSs). The fabricated ASSs on LiNbO3 exhibit an average transmittance improvement from 78% to 85% at 3–5 µm, and a high transmittance of 88% is achieved at 5 µm.