Realization of High Aspect Ratio Anti-reflection Structures via Laser Irradiation inside Liquid

Anti-reflection structures (ARS) in micro/nano-scales provide remarkable opportunities for broadband and omnidirectional anti-reflection performance. In this work, laser-induced surface structures at a high aspect ratio of 3.4 and a period of 50 m are firstly created on crystalline silicon wafers by nanosecond pulsed laser ablation in air. Meanwhile, a high aspect ratio of 5.0 structures for enhanced light trapping are realized via laser ablation inside water. Such enhancement is attributed to the limitation of plasma inside water. The processing rate is increased by 2.34 times with the localized chemical etching inside NaOH solution. The average reflection of 3.28% is achieved from 380 to 780 nm, 15% lower than laser ablation in air. Laser ablation with the liquid assistance provides a new method to generate high aspect ratio ARS.