Transverse-mode coupling effects in scanning cavity microscopy

TL;DR

This paper investigates how microscopic mirror surface imperfections affect the performance of high-resolution scanning cavity microscopy, revealing the roles of resonant and non-resonant mode coupling caused by surface topography.

Contribution

It provides a detailed analysis of transverse-mode coupling effects in scanning cavity microscopy due to mirror surface imperfections, enhancing understanding of imaging limits.

Findings

Localized cavity transmission reductions from resonant mode coupling

Background patterns caused by micro-roughness of mirrors

Impact of mirror topography on imaging accuracy

Abstract

Tunable open-access Fabry-P\'erot microcavities enable the combination of cavity enhancement with high resolution imaging. To assess the limits of this technique originating from background variations, we perform high-finesse scanning cavity microscopy of pristine planar mirrors. We observe spatially localized features of strong cavity transmission reduction for certain cavity mode orders, and periodic background patterns with high spatial frequency. We show in detailed measurements that the localized structures originate from resonant transverse-mode coupling and arise from the topography of the planar mirror surface, in particular its local curvature and gradient. We further examine the background patterns and find that they derive from non-resonant mode coupling, and we attribute it to the micro roughness of the mirror. Our measurements and analysis elucidate the impact of imperfect mirrors and reveal the influence of their microscopic topography. This is crucial for the interpretation of scanning cavity images, and could provide relevant insight for precision applications such as gravitational wave detectors, laser gyroscopes, and reference cavities.