Comparative Study on Grating Fabrication in Transparent Materials by TWIN-LIBWE and Ultrashort Pulsed Ablation Techniques

Abstract

Two methods for micro-structuring of transparent dielectric were compared in this study: the two-beam interferometric laser-induced backside wet etching (TWIN-LIBWE) and the two beam interferometric ablation by ultrashort laser pulses. In TWIN-LIBWE we used the 4 th harmonic of Nd:YAG laser (λ=266 nm, τFWHM=8 ns, fuence: 265-500 mJ/cm 2 ), while a Ti:Sapphire-based femtosecond system (λ=800 nm, τFWHM=30 fs, pulse energy: 600-900 µJ) was used for direct ablation. Fused silica, sapphire and glass were used as bulk targets, while Al2O3, Y2O3, HfO2 and ZrO2 thin films (thickness: 160-1000 nm) on fused silica substrates were used as transparent film targets. The incident angle of the interfering beams was adjusted to result in 1 µm period structures in both arrangements. The surface morphologies of gratings were studied by atomic force microscope (AFM). After the comparison of best quality gratings produced by both setup in each material, we cannot determined which is the universally optimal method. The grating quality depends on the target material, their thickness, and certainly on the laser parameter.