Integrating high-precision and fringe-scale displacement sensing using heterodyne cavity-tracking

TL;DR

This paper introduces a heterodyne cavity-tracking interferometer that combines high precision and fringe-scale range, achieving sub-femtometer sensitivity and a dynamic range of 0.15 micrometers for displacement sensing.

Contribution

The authors develop a compact heterodyne cavity-tracking scheme that significantly enhances displacement measurement range while maintaining high sensitivity.

Findings

Achieved a sensitivity of 260 fm/√Hz at 1 Hz

Demonstrated a dynamic range of 0.15 μm for displacement

Reaches a sub-femtometer noise floor theoretically

Abstract

We present a heterodyne stabilized cavity-based interferometer scheme that can serve as a compact and high-sensitivity displacement sensor with a fringe-scale operating range. The technique, in principle, can reach a sub-femtometer noise floor and an operating range on the order of one laser wavelength at $\lambda \approx 1\,\mu m$. With our current experimental setup, we achieve a sensitivity of about $260 fm/\sqrt{\mathrm{Hz}}$ at $1\,Hz$ and $46 fm/\sqrt{\mathrm{Hz}}$ at around $130\,Hz$. By probing a length actuated cavity, we demonstrate six orders of magnitude of dynamic range for displacement measurement, reaching a maximum motion of $0.15\,\mu m$. The tracking bandwidth and displacement range are limited by analog effects in the signal digitization and are extendable in the future.