Free space experimental characterization of a multilayer Fabry-Pérot resonator for DALI

The axion is a long-postulated boson that can simultaneously solve two crucial problems of Modern Physics: the unexpected charge and parity symmetry observed in the strong nuclear force and the enigma of dark matter. The Dark-photons and Axion- Like particles Interferometer (DALI) is a proposal for a new generation axion detector designed to probe dark matter in a broad band that ranges from microwaves to mm-wave employing a tunable multilayer Fabry-Pérot interferometer. This frequency range remains poorly explored owing to the technological challenges associated with the development of the experimental approach required to scan it. The DALI instrument, which is currently in the prototyping phase, imports technology and techniques from radio astronomy. This apparatus may also be sensitive to other hypothetical particles, such as the dark photon.

A resonator is needed to enhance the weak signal originating from axion to photon conversion by the action of an external magnetic field. It is composed of ceramic plates and an electro-mechanical tuner. A fixed-plate prototype of a resonator has been manufactured and tested in an optical laboratory setup devised to excite it with a horn antenna and observe its resonant spectral feature from reflectivity measurements. A detailed description of the setup, the post-processing of the data and the observed resonant structure are treated in this work.