  We present the fabrication of exceptionally small-radius concave microoptics
on fused silica substrates using CO2 laser ablation and subsequent reactive ion
etching. The protocol yields on-axis near-Gaussian depressions with radius of
curvature $\lesssim5$ microns at shallow depth and low surface roughness of 2
angstroms. This geometry is appealing for cavity quantum electrodynamics where
small mode volumes and low scattering losses are desired. We study the optical
performance of the structure within a tunable Fabry-Perot type microcavity,
demonstrate near-coating-limited loss rates (F = 25,000) and small focal
lengths consistent with their geometrical dimensions.
