Relativistic coupling of phase and amplitude noise in optical interferometry

TL;DR

This paper investigates how relativistic effects cause coupling between phase and amplitude noise in optical interferometers, even when optical elements move purely along the axis, potentially impacting measurement sensitivity.

Contribution

It introduces a relativistic correction mechanism for noise coupling in optical interferometry, which had not been previously considered.

Findings

Relativistic effects induce measurable phase and amplitude noise coupling.

The effect scales with the velocity of optical elements relative to the speed of light.

Potential limitations on interferometer sensitivity due to relativistic noise coupling.

Abstract

Extraneous motion of optical elements in an interferometer lead to excess noise. Typically, fluctuations in the effective path length lead to phase noise, while beam-pointing leads to apparent amplitude noise. For a transmissive optic moving along the optical axis, neither effect should exist. However, relativity of motion suggests that even in this case, small corrections of order $v/c$ ($v$ the velocity of the optic), give rise to phase and amplitude noise on the light. Here we calculate the effect of this relativistic mechanism of noise coupling, and discuss when such an effect would limit the sensitivity of optical interferometers.