Optimized single-shot laser ablation of concave mirror templates on optical fibers*

In recent years, techniques have been developed to realize concave mirror templates on the tip of optical fibers. These can be used to define tunable open-access Fabry-Perot microcavities with high finesse. The combination of spectral tunability, high finesse, intrinsic fiber coupling and uniquely small dimensions offered by these optical cavities has led to their widespread adoption in the cavity quantum electrodynamics (CQED) community and to a lesser extent in the optomechanics community.
We realize mirror templates on the tips of optical fibers using a single-shot CO2 laser ablation procedure. We perform a systematic study of the influence of the pulse power, pulse duration, and laser spot size on the radius of curvature, depth, and diameter of the mirror templates. We find that these geometrical characteristics can be tuned to a larger extent than has been previously reported, and notably observe that compound convex-concave shapes can be obtained. This detailed investigation should help further the understanding of the physics of CO2 laser ablation processes and help improve current models. We additionally identify regimes of ablation parameters that lead to mirror templates with favorable geometries for use in cavity quantum electrodynamics and optomechanics.