Decoding the interference signal in white light interferometry for precision temperature sensing

Abstract

Thermal fluctuations have a key role in the performance of LISA space mission, which aims to detect gravitational waves. Equipment based on White Light Interferometry (WLI) is a promising technology to measure microkelvin thermal fluctuations at very low frequencies. The aim of this project, carried out by IEEC researchers, is to achieve measuring temperature fluctuations as low as 1 μK/√Hz in the 1 Hz down to 0.1 mHz range. The interference output signal obtained by the photodiode utilized in IEEC installations is described using a physical model, where the measured intensity is deduced from the interaction of electromagnetic waves within the equipment. Expressions for the outputs of the sensing and reference interferometers are provided, allowing for the absolute temperature measurement through the utilization of the cross-correlation function between the reference and sensing signals. It is shown that the adjustment of the coherence length of the incident white light facilitates the measurement process by reducing sensitivity to noise