Photothermal effects in ultra-precisely stabilized tunable microcavities

TL;DR

This paper demonstrates ultra-precise stabilization of tunable microcavities using electronic and photothermal effects, revealing self-oscillations and achieving high feedback bandwidth and stability under ambient conditions.

Contribution

It introduces a novel combination of electronic and photothermal stabilization techniques to enhance microcavity stability and explores photothermal effects causing self-oscillations.

Findings

Photothermal mirror expansion improves cavity stability by nearly two orders of magnitude.

Self-oscillations occur at high intracavity power due to photothermal instability.

Achieved a feedback bandwidth of 500 kHz with a noise level of 1.1×10⁻¹³ m rms.

Abstract

We study the mechanical stability of a tunable high-finesse microcavity under ambient conditions and investigate light-induced effects that can both suppress and excite mechanical fluctuations. As an enabling step, we demonstrate the ultra-precise electronic stabilization of a microcavity. We then show that photothermal mirror expansion can provide high-bandwidth feedback and improve cavity stability by almost two orders of magnitude. At high intracavity power, we observe self-oscillations of mechanical resonances of the cavity. We explain the observations by a dynamic photothermal instability, leading to parametric driving of mechanical motion. For an optimized combination of electronic and photothermal stabilization, we achieve a feedback bandwidth of $500\,$kHz and a noise level of $1.1 \times 10^{-13}\,$m rms.