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

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 <i>λ</i> ≈ 1 μm. With our current experimental setup, we achieve a sensitivity of about 260 <i>f</i> <i>m</i>/Hz at 1 Hz and 46 <i>f</i> <i>m</i>/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 μm. The tracking bandwidth and displacement range are limited by analog effects in the signal digitization and are extendable in the future.