Resonantly Enhanced Axion-Photon Regeneration

We point out that photon regeneration-experiments that search for the axion,or axion-like particles, may be resonantly enhanced by employing matchedFabry-Perot optical cavities encompassing both the axion production andconversion magnetic field regions. Compared to a simple photon regenerationexperiment, which uses the laser in a single-pass geometry, this technique canresult in a gain in rate of order ${\cal F}^2$, where ${\cal F}$ is the finesseof the cavities. This gain could feasibly be $10^{(10-12)}$, corresponding toan improvement in sensitivity in the axion-photon coupling, $g_{a\gamma\gamma}$, of order ${\cal F}^{1/2} \sim 10^{(2.5-3)}$, permitting a practical purelylaboratory search to probe axion-photon couplings not previously excluded bystellar evolution limits, or solar axion searches.Comment: 4 pages, 2 figure