Scalable fabrication of ultrahigh-finesse micromirrors with variable geometry

Due to their unrivaled performance and versatility, high-finesse Fabry-P\'erot resonators have enabled scientific and technological breakthroughs in fields ranging from cavity QED to optical clocks and precision metrology. Scalable production of compact Fabry-P\'erot resonators could enable miniaturaization and integration of these technologies for new applications. However, it has proven difficult to identify a microfabrication approach that can yield world-class resonator performance and produce the range of required resonator geometries. In this paper, we demonstrate a wafer-scale fabrication technique that produces arrays of ultrahigh-finesse ($\geq 10^6$) mirrors with a user-defined radius of curvature spanning four orders of magnitude ($10^{-4}-10^0$ m). We employ photoresist reflow and reactive ion etching to shape and transfer mirror templates into a substrate while maintaining sub-Angstrom roughness. This substrate is coated and used to create arrays of compact Fabry-P\'erot resonators with finesse values as high as 1.3 million and measured excess loss $< 1$ ppm. Optical ringdown measurements of 43 devices across 5 substrates reveal that the fabricated cavity mirrors with both small and large radii of curvature produce an average coating-limited finesse of 1.05 million. This versatile new approach opens the door to scalable fabrication of high-finesse miniaturized Fabry-P\'erot cavities needed for next-generation quantum optics and frequency metrology technologies.