Our paper Fabrication of mirror templates in silica with micron-sized radii of curvature was published in Applied Physics Letters. Routinely, we use a laser ablation process to create mirror templates in silica, usually on flat substrates but also on the end facets of optical fibres. For cavity QED applications, the mode volume should be small. We therefore strive to make the radius of curvature as small as possible. However, while the standard process can produce radii down to 5 microns or so, there is a strong correlation between radius and depth – as the radius decreases, the depth increases – such that the smallest radii templates do not support stable cavity modes. In this paper we describe two techniques which allow shallow, small-radius mirror templates to be fabricated. The essential advantage of the laser ablation technique, the creation of super-smooth surfaces, is retained and we demonstrate stable, small-radius microcavity modes with mirror-limited finesse values up to 25,000.
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