On the sensitivity of a laser heterodyne polarimeter for vacuum birefringence detection

Abstract

Detecting vacuum magnetic birefringence (VMB) requires an immensely accurate, precisely calibrated experiment. We are working on a new design to detect the birefringence (BF) of individual optical components without a cavity that can also be used to measure VMB in reflection off a cavity. Our design uses two overlapping, orthogonally polarized laser beams to measure the relative phase difference between a reference path and one with rotating polarizations, which may experience oscillating phase shifts in vacuum in the presence of a magnetic field. To test the design, we developed a small-scale setup without cavities that can analyze different birefringent sources with the same principle. Our early results from testing mirrors show spatial variations in BF due to imperfect mirror coatings and show no correlation between the strength of a magnetic field applied parallel to the mirror’s surface and BF amplitude. In addition to assisting in the selection of suitable components for the final design, our laser heterodyne polarimeter (LHP) promises more sensitive results than previous experiments and may very well be the basis for the very first detection of VMB.