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

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 $\hat{I}»\approx 1\hat{I}¼m$. With our current experimental setup, we achieve a sensitivity of about $260fm/\sqrt{\mathrm{Hz}}$ at $1Hz$ and $46fm/\sqrt{\mathrm{Hz}}$ at around $130Hz$. By probing a length actuated cavity, we demonstrate six orders of magnitude of dynamic range for displacement measurement, reaching a maximum motion of $0.15\hat{I}¼m$. The tracking bandwidth and displacement range are limited by analog effects in the signal digitization and are extendable in the future.

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