Observation of photo-thermal feed-back in a stable dual-carrier optical spring

TL;DR

This paper reports the experimental observation of photo-thermal feedback in a dual-carrier optical spring system, demonstrating how absorption-induced effects influence stability and proposing modifications for improved control.

Contribution

It provides the first measurement of photo-thermal feedback in a stable dual-carrier optical spring and suggests coating modifications to achieve stability.

Findings

Photo-thermal feedback observed and characterized.

Feedback tends to destabilize the optical spring.

Proposed coating modification can reverse feedback sign.

Abstract

We report on the observation of photo-thermal feed-back in a stable dual-carrier optical spring. The optical spring is realized in a 7 cm Fabry-Perot cavity comprised of a suspended 0.4 g small end mirror and a heavy input coupler, illuminated by two optical fields. The frequency, damping and stability of the optical spring resonance can be tuned by adjusting the power and detuning of the two optical fields, allowing for a precise measurement of the absorption-induced photo-thermal feedback. The magnitude and frequency dependence of the observed photo-thermal effect are consistent with predicted corrections due to transverse thermal diffusion and coating structure. While the observed photo-thermal feed-back tends to destabilize the optical spring, we also propose a small coating modification that would change the sign of the effect, making a single-carrier stable optical spring possible.