Investigation of ultrafast laser stress generation in fused silica, Corning Eagle XG glass, Corning ULE glass, and sapphire

Previous work has demonstrated the feasibility of using ultrafast laser generated stress to deform fused silica substrates to a desired flatness in a process called ultrafast laser stress figuring (ULSF). Materials other than fused silica may offer superior optomechanical properties that are more suited to certain applications or environments. In this work we explore the stress generated by focused ultrafast laser pulses in several common optical materials: Corning Ultra Low Expansion (ULE) glass, Corning Eagle XG glass, fused silica, and sapphire. Using a laser polarization state perpendicular to the writing direction, we find that the laser induced stress depends on the energy of the ultrafast laser pulses, the distance between two adjacent focused pulses, and the repetition rate at which the pulses are delivered into the material. Each material explored showcases unique dependence on these parameters. The results from this investigation will be used to characterize the potential equivalent material removal rates that would be theoretically achievable by ultrafast laser stress figuring for commercially available sapphire and Eagle XG substrates.