Deep phase modulation interferometry

TL;DR

This paper introduces a novel method for homodyne interferometers that maintains high sensitivity over many fringes, enabling continuous real-time tracking of length and angle with exceptional precision.

Contribution

The authors extend existing phase modulation techniques to achieve stable, high-sensitivity measurements over extended periods, suitable for real-time applications.

Findings

Achieved 0.1 mrad/√Hz sensitivity in phase over thousands of seconds

Demonstrated 20 pm/√Hz length measurement sensitivity

Achieved 10 nrad/√Hz angular measurement sensitivity at millihertz frequencies

Abstract

We have developed a method to equip homodyne interferometers with the capability to operate with constant high sensitivity over many fringes for continuous real-time tracking. The method can be considered as an extension of the "J_1...J_4" methods, and its enhancement to deliver very sensitive angular measurements through Differential Wavefront Sensing is straightforward. Beam generation requires a sinusoidal phase modulation of several radians in one interferometer arm. On a stable optical bench, we have demonstrated a long-term sensitivity over thousands of seconds of 0.1 mrad/sqrt[Hz] that correspond to 20 pm/sqrt[Hz] in length, and 10 nrad/sqrt[Hz] in angle at millihertz frequencies.