Fabrication of mirror templates in silica with micron-sized radii of curvature

TL;DR

This paper reports a method to fabricate tiny concave silica microoptics with very small radii of curvature, suitable for quantum optics applications, achieving high optical quality and low surface roughness.

Contribution

The authors developed a novel fabrication protocol combining CO2 laser ablation and reactive ion etching to produce microoptics with radii of curvature less than 5 microns on silica substrates.

Findings

Achieved surface roughness of 2 angstroms.

Demonstrated high finesse (F=25,000) in microcavities.

Produced small focal lengths consistent with geometry.

Abstract

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.