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Abstract

Axions have attracted attention promising candidates for dark matter (DM).
Although axions have been intensively searched for, they have not been observed
yet. Recently, novel experiments to search for axion DM have been proposed that
use optical cavities to amplify polarization rotation of laser light induced by
the axion-photon interaction. One such experiment employs a ring cavity
composed of four mirrors. However, its sensitivity to the axion-photon coupling
$\gag$ in the low axion mass region is limited due to the reflection phase
difference between s- and p-polarizations. In this paper, we propose a new
method to improve the sensitivity using zero-phase shift mirrors and a
wavelength tunable laser. Moreover, the laser makes it easier to scan the high
axion mass region by tuning the reflection phase difference between s- and
p-polarizations. We experimentally confirmed that the phase difference
generated upon reflection on a zero phase shift mirror satisfies the
requirement of $8.6 \times 10^{-3}~\si{deg}$, which corresponds to the half
width at half maximum (HWHM) of the p-polarization with the mirror fixed on a
folded cavity and a wavelength tunable laser.