Year: 2026
Type: preprint
Abstract: We present the Axion Polarimetric Experiment (APE), a cavity-enhanced polarimeter designed to search for ultralight axion and axion-like-particle dark matter through a time-dependent rotation of the linear polarization of laser light. In cavity-based schemes, intracavity quarter-wave plates can restore coherent buildup of the axion-induced orthogonal polarization, but their transmissive loss limits the achievable finesse. To avoid transmissive intracavity optics, we propose a folded Fabry-Perot cavity that employs dielectric phase-shifting mirrors. At an incidence angle near $45^\circ$, these mirrors provide a reflection-phase difference $Δϕ\equiv ϕ_s-ϕ_p \simeq π/2$ between $s$ and $p$ polarizations and therefore act as reflective quarter-wave plates. We present the coating design, thickness optimization, and measurements of the phase shift and optical loss of the phase-shifting mirrors. Using a heterodyne polarimetric readout and an explicitly stated noise model, we derive design-level sensitivity projections for the axion-photon coupling $g_{aγγ}$. These projections should be interpreted as target sensitivities for the proposed cavity configuration, since the full-system birefringence noise and angular-jitter coupling remain to be measured.
Source: arXiv (Cornell University)
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: Deutsche Forschungsgemeinschaft
OpenAlex ID: W7167013640
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