Strategies for Improving Ultrafast Laser Stress Figuring Range and Resolution

Optical stress figuring relies on the precise generation of stress fields to bend an optical component to a final desired shape. Previous work by our group shows that our in-house ultrafast laser stress figuring (ULSF) system can accurately flatten large aspect ratio fused silica mirrors (both dielectric and aluminum coated). Our current system and process allows us to take fused silica mirrors (100 mm diameter, 1 mm thick) with 5 mu m RMS amplitude and correct them down to <20 nm RMS over 6 orders of Zernike polynomials. The current process throughput is similar to other deterministic figuring techniques but could be orders of magnitude faster with the currently available laser power. To expand our production capabilities to accommodate rapid generation of free-form optical shapes, we will need to be able to generate larger magnitudes of stress in shorter amounts of time while maintaining or improving our current accuracy. To lay the groundwork towards this, we investigated three strategies to increase stress generation magnitude and improve stress generation resolution. Here we present results showing 5.22 x improvement in achievable stress magnitude and also present a method to generate arbitrarily small stress fields.