# Control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry

## TL;DR

This paper demonstrates real-time control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry, achieving high sensitivity and potential applications in gravitational-wave detection.

## Contribution

It introduces a novel digitally-enhanced heterodyne interferometry method for real-time control of suspended optical cavities, suitable for complex interferometric systems.

## Key findings

- Achieved a peak sensitivity of ~10 pm/√Hz over 10-1000 Hz.
- First demonstration of closed-loop control of an independently suspended Fabry-Perot cavity.
- Method is extensible to multiple coupled cavities, relevant for gravitational-wave detectors.

## Abstract

We present the first demonstration of real-time closed-loop control and deterministic tuning of an independently suspended Fabry-Perot optical cavity using digitally-enhanced heterodyne interferometry, realising a peak sensitivity of $\sim$10 pm$/\sqrt{\mathrm{Hz}}$ over the 10-1000 Hz frequency band. The methods presented are readily extensible to multiple coupled cavities. As such, we anticipate that refinements of this technique may find application in future interferometric gravitational-wave detectors.