Detailed design of a resonantly-enhanced axion-photon regeneration experiment

TL;DR

This paper proposes a resonantly-enhanced photon-regeneration experiment using Fabry-Perot cavities to significantly improve the sensitivity in detecting axion-like particles, potentially surpassing astrophysical limits.

Contribution

It introduces a detailed design for a resonantly-enhanced axion-photon regeneration experiment employing matched optical cavities for the first time.

Findings

Potential sensitivity improvement of up to 10^10 in axion-photon coupling detection.

Feasibility of a purely laboratory experiment surpassing stellar and solar axion search limits.

Detailed control scheme for the cavities and laser frequencies described.

Abstract

A resonantly-enhanced photon-regeneration experiment to search for the axion or axion-like particles is described. This experiment is a shining light through walls study, where photons travelling through a strong magnetic field are (in part) converted to axions; the axions can pass through an opaque wall and convert (in part) back to photons in a second region of strong magnetic field. The photon regeneration is enhanced by employing matched Fabry-Perot optical cavities, with one cavity within the axion generation magnet and the second within the photon regeneration magnet. Compared to simple single-pass photon regeneration, this technique would result in a gain of (F/pi)^2, where F is the finesse of each cavity. This gain could feasibly be as high as 10^(10), corresponding to an improvement in the sensitivity to the axion-photon coupling, g_(agg), of order (F/pi)^(1/2) ~ 300. This improvement would enable, for the first time, a purely laboratory experiment to probe axion-photon couplings at a level competitive with, or superior to, limits from stellar evolution or solar axion searches. This report gives a detailed discussion of the scheme for actively controlling the two Fabry-Perot cavities and the laser frequencies, and describes the heterodyne signal detection system, with limits ultimately imposed by shot noise.