Precise etching of fused silica for micro-optical applications

The current challenge of laser processing is the high quality etching of transparent materials for micro-optical applications. Laser ablation of transparent material with UV and ultrashort pulse lasers is characterized by a high etch rate and a considerable surface roughness. The combination of specific laser processing techniques, e.g., scanning contour mask technique and direct writing with a small laser spot, with laser-induced backside wet etching (LIBWE) allows both the direct machining of diffractive as well as refractive topographies into dielectric materials with almost optical quality. The etching of variable depth gratings and free-form surface topographies with a PV-value of less than 500 nm, a nanometer depth resolution, and a low roughness of less than 10 nm rms is presented and demonstrates the capabilities of this laser processing approach.