Investigation and mitigation of noise contributions in a compact heterodyne interferometer

TL;DR

This paper introduces a noise estimation and subtraction algorithm that significantly enhances the sensitivity of heterodyne laser interferometers, enabling more precise dynamic measurements in inertial sensing applications.

Contribution

The paper presents a novel noise correction algorithm applicable to heterodyne laser interferometers, improving sensitivity by an order of magnitude through targeted noise source removal.

Findings

Achieved a noise floor of 3.31E-11 m/rtHz at 100mHz after noise subtraction.

Demonstrated effective removal of non-linear optical pathlength, laser frequency, and temperature noise.

Validated the algorithm on a benchtop prototype in vacuum conditions.

Abstract

We present a noise estimation and subtraction algorithm capable of increasing the sensitivity of heterodyne laser interferometers by one order of magnitude. The heterodyne interferometer is specially designed for dynamic measurements of a test mass in the application of sub-Hz inertial sensing. A noise floor of 3.31E-11 m/rtHz at 100mHz is achieved after applying our noise subtraction algorithm to a benchtop prototype interferometer that showed a noise level of 2.76E-10 m/rtHz at 100mHz when tested in vacuum at levels of 3E-5 Torr. Based on the previous results, we investigated noise estimation and subtraction techniques of non-linear optical pathlength noise, laser frequency noise, and temperature fluctuations in heterodyne laser interferometers. For each noise source, we identified its contribution and removed it from the measurement by linear fitting or a spectral analysis algorithm. The noise correction algorithm we present in this article can be generally applied to heterodyne laser interferometers.