Precision Measurement Using Disorder

High-finesse Fabry-Perot cavities are used to measure and lock laser frequencies down to linewidths on the order of 1 Hz. However, precise and unambiguous measurement of the frequency requires prior knowledge of the approximate laser frequency. If the laser is instead passed through a low-loss multi-path interferometer (MPI), the resulting intensity signals at the output ports may be computationally inverted to extract the laser frequency. This method is in principle highly sensitive to all wavelength changes and unambiguous in determining the frequency. In this work, we present the experimental realization of an MPI based on a modified Herriott cell that generates speckle patterns with unique dependence on the input frequency. We also demonstrate that a principal component analysis of the images can efficiently encode information about the interference patterns and track drifts caused by environmental disturbances.