Micro-mirror laser machining for ultra-low birefringence cavities

The development of high-finesse optical micro-cavities has significantly advanced applications in spectroscopy, quantum optics, and sensing. We introduce a novel CO 2 laser machining method for fabricating optical micro-mirrors with high concentricity, as well as ultra-low birefringence and surface roughness. This process, which involves spinning the substrate at high speeds during machining, improves on previous methods in both the time and complexity of the process while also achieving superior mirror symmetry. We demonstrate the production of micro-mirrors with radii of curvature ranging from 100 μ m to 700 μ m, achieving surfaces with roughness below 0.15 nm and scattering losses as low as 4 ppm at 854 nm. Cavities made with these mirrors exhibit no measurable birefringence and their low scattering losses suggest that cavity finesses exceeding 600,000 at 854 nm are possible.