Active stabilization of an open-access optical microcavity for low-noise operation in a standard closed-cycle cryostat

Abstract

Open-access optical microcavities are Fabry–Perot type cavities consisting of two micrometer-size mirrors, separated by an air (or vacuum) gap typically of a few micrometers. Compared to integrated microcavities, this configuration is more flexible as the relative position of the two mirrors can be tuned, allowing for easy changes in parameters such as cavity length and mode volume and the selection of specific transverse cavity modes. These advantages come at the expense of the mechanical stability of the cavity itself, which is particularly relevant in noisy closed-cycle cryostats. Here, we show an open-access optical microcavity based on scanning-probe microscope design principles. When operated at 4 K in a tabletop optical closed-cycle cryostat without any dedicated mechanical low-pass filter, we obtain stabilities of 5.7 and 10.6 pm rms in the quiet and full periods of the cryocooler cycle, respectively. Our device has free-space optical access, essential, for instance, for full polarization control.