Thermal stability of ultrafast laser-generated stress in fused silica

Ultrafast Laser Stress Figuring (ULSF) is a new process for shaping thin optics. The stability of ULSF generated stress, at room temperature and at elevated temperatures, is unknown. Exposing laser-figured samples to elevated temperature acts as a proxy for testing long-term stability of ultrafast laser-generated stress. We conducted an isochronal annealing study up to 500 °C, on fused silica wafers, figured with single-Zernike deformation components, measuring their shape after each cycle. We track changes in those deformations, demonstrating that figured samples show small amounts of relaxation under increasing temperature, beginning around 200-300 °C. This suggests ULSF produces stable mirror figuring only up to ~200 °C temperatures. Combined with previous measurements, this suggests ULSF may exhibit long-term stability at room-temperature.