Intrinsic mirror noise in Fabry-Perot based polarimeters: the case for the measurement of vacuum magnetic birefringence

Abstract

Although experimental efforts have been active for about 30 years now, a direct laboratory observation of vacuum magnetic birefringence, an effect due to vacuum fluctuations, still needs confirmation. Indeed, the predicted birefringence of vacuum is $\Delta n=4.0\times 10^{-24}$ @ 1~T. One of the key ingredients when designing a polarimeter capable of detecting such a small birefringence is a long optical path length within the magnetic field and a time dependent effect. To lengthen the optical path within the magnetic field a Fabry-Perot optical cavity is generally used with a finesse ranging from $\mathcal{F}\approx 10^4$ to $\mathcal{F}\approx 7\times 10^5$. Interestingly, there is a difficulty in reaching the predicted shot noise limit of such polarimeters. We have measured the ellipticity and rotation noises along with a Cotton-Mouton and a Faraday effect as a function of the finesse of the cavity of the PVLAS polarimeter. The observations are consistent with the idea that the cavity mirrors generate a birefringence-dominated noise whose ellipticity is amplified by the cavity itself. The optical path difference sensitivity at $10$Hz is $S_{\Delta \mathcal{D}}=6\times 10^{-19}$m$/\sqrt{\mathrm{Hz}}$, a value which we believe is consistent with an intrinsic thermal noise in the mirror coatings.

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Cited by in corpus (7)

• Monte Carlo study of the BMV vacuum linear magnetic birefringence experiment
• Effects of mirror birefringence and its fluctuations to laser interferometric gravitational wave detectors
• Polarimetry for measuring the vacuum magnetic birefringence with quasi-static fields: a systematics study for the VMB@CERN experiment
• Astrophysics in Strong Electromagnetic Fields and Laboratory Astrophysics
• The PVLAS experiment: a 25 year effort to measure vacuum magnetic birefringence
• Magnetic response from constant backgrounds to Coulomb sources
• Singular electromagnetic fields in nonlinear electrodynamics with a constant background field