2018/05/08 by G. Zavattini, F. Della Valle, A. Ejlli +6
Biochemistry, Genetics and Molecular Biology · Decision Sciences · Physics and Astronomy · #Birefringence #Fabry–Pérot interferometer #Faraday cage #Faraday effect #Finesse #Geomagnetism and Paleomagnetism Studies #Laser #Magnetic field #Noise (video) #Optical path #Optical path length #Optics #Physics #Polarimeter #Polarimetry #Quantum mechanics #Scattering #Scientific Measurement and Uncertainty Evaluation #Stellar, planetary, and galactic studies #hep-ex #physics.ins-det #physics.optics
paper · pdf · doi:10.1140/epjc/s10052-018-6063-y
arxiv created 2018/05/08 · openalex created_date 2018/05/17 · openalex publication_date 2018/07/01 · arxiv updated 2018/08/15 · openalex updated_date 2026/08/05
Although experimental efforts have been active for about 30 years, a direct laboratory observation of vacuum magnetic birefringence, due to vacuum fluctuations, still needs confirmation: the predicted birefringence of vacuum is Δ n = 4.0× 10-24 @ 1 T. Key ingredients of a polarimeter for detecting such a small birefringence are a long optical path within the magnetic field and a time dependent effect. To lengthen the optical path a Fabry–Perot is generally used with a finesse ranging from \mathscr F ≈ 104 to \mathscr F ≈ 7× 105 . 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 Cotton-Mouton and Faraday effects 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 \hbox Hz is S_Δ \mathscr D=6× 10-19 \hbox m/√(Hz) , a value which we believe is consistent with an intrinsic thermal noise in the mirror coatings. Our findings prove that the continuous efforts to increase the finesse of the cavity to improve the sensitivity has reached a limit.