Towards freeform reflective fused silica optics using ultrafast laser-assisted etching

Image slicers are key components in many astronomical instruments, notably in the VLT-MUSE instrument. However, the precision manufacturing of image slicers is costly and time-consuming. One technology that could transform the manufacturing of fused silica image slicers is ultrafast laser-assisted etching (ULAE), as it enables micron-level precision shaping of fused silica over multi-mm scales. In this paper, we demonstrate the fabrication of a 10 x 1 mm fused silica surface with ~700 nm (peak-to-valley) surface form error and ~70 nm (rms) roughness. If combined with post-processing polishing techniques, such as CO2 laser polishing, ULAE could yield high-performance freeform fused silica image slicers for diverse applications, including astronomy.