High Frame-Rate Phase Camera for High-Resolution Wavefront Sensing in Gravitational-Wave Detectors

TL;DR

This paper introduces a high-resolution, high-frame-rate phase camera using a commercial CMOS sensor for wavefront sensing in gravitational-wave detectors, capable of detecting nanometer-scale optical path distortions.

Contribution

The work demonstrates a novel application of a commercially available CMOS phase camera for high-precision wavefront sensing in gravitational-wave detectors, enabling improved alignment diagnostics.

Findings

Capable of sensing optical path distortions >2 nm in LIGO mirrors

Achieves phase resolution down to -62 dBc/second/pixel

Performance reaches 0.1 nm in homodyne readout

Abstract

We present a novel way of wavefront sensing using a commercially available, continuous-wave time-of-flight camera with QVGA-resolution. This CMOS phase camera is capable of sensing externally modulated light sources with frequencies up to 100 MHz. The high-spatial-resolution of the sensor, combined with our integrated control electronics, allows the camera to image power modulation index as low as -62 dBc/second/pixel. The phase camera is applicable to problems where alignment and mode-mismatch sensing is needed and suited for diagnostic and control applications in gravitational-wave detectors. Specifically, we explore the use of the phase camera in sensing the beat signals due to thermal distortions from point-like heat absorbers on the test masses in the Advanced LIGO detectors. The camera is capable of sensing optical path distortions greater than about two nanometers in the Advanced LIGO input mirrors, limited by the phase resolution. In homodyne readout, the performance can reach up to 0.1 nm, limited by the modulation amplitude sensitivity.