Differential wavefront sensing and control using radio-frequency optical demodulation

TL;DR

This paper introduces a novel optical demodulation technique for differential wavefront sensing, achieving higher resolution measurements and effective wavefront error correction in interferometric setups, with potential applications in complex optical systems.

Contribution

The paper presents a new optical demodulation method for differential wavefront sensing that enhances resolution and enables closed-loop wavefront correction using commercial equipment.

Findings

Achieved 99.9% mode-matching into an optical cavity.

Demonstrated digital processing of optical images for wavefront error signals.

Showed potential for correcting higher order wavefront errors.

Abstract

Differential wavefront sensing is an essential technique for optimising the performance of many precision interferometric experiments. Perhaps the most extensive application of this is for alignment sensing using radio-frequency beats measured with quadrant photodiodes. Here we present a new technique that uses optical demodulation to measure such optical beats at significantly higher resolutions using commercial laboratory equipment. We experimentally demonstrate that the images captured can be digitally processed to generate wavefront error signals and use these in a closed loop control system for correct wavefront errors for alignment and mode-matching a beam into an optical cavity to 99.9\%. This experiment paves the way for the correction of even higher order errors when paired with higher order wavefront actuators. Such a sensing scheme could find use in optimizing complex interferometers consisting of coupled cavities, such as those found in gravitational wave detectors, or simply just for sensing higher order wavefront errors in heterodyne interferometric table-top experiments.