Improving ellipticity detection sensitivity for the Q & A vacuum birefringence experiment

TL;DR

This paper discusses advancements in ellipticity detection sensitivity for the Q & A vacuum birefringence experiment, including new optical components and control schemes to enhance measurement precision.

Contribution

The paper introduces a new scheme and control methods to improve ellipticity detection sensitivity in the Q & A experiment, surpassing previous limitations.

Findings

Enhanced ellipticity detection sensitivity achieved.

Implementation of new polarizers with extinction ratio below 10^{-8}.

Design of automatic alignment control for better measurement accuracy.

Abstract

Q & A (quantum electrodynamics test and search for axion) experiment was first proposed in 1994 and a 3.5 m high-finesse Fabry-Perot prototype detector extendable to 7 m has been built and tested. We now enter into the 2nd phase of improving the ellipticity detection sensitivity. We present our scheme, compare with other ongoing experiments, analyze the displacement spectra of our suspension system, and use them for designing automatic alignment control to improve the ellipticicy detection sensitivity. To improve ellipsometry resolution, we use new polarizers of extinction ratio smaller than 10^{-8}.