title: Note: In situ measurement of vacuum window birefringence by atomic spectroscopy.
abstract: We present an in situ method to measure the birefringence of a single vacuum window by means of microwave spectroscopy on an ensemble of cold atoms. Stress-induced birefringence can cause an ellipticity in the polarization of an initially linearly polarized laser beam. The amount of ellipticity can be reconstructed by measuring the differential vector light shift of an atomic hyperfine transition. Measuring the ellipticity as a function of the linear polarization angle allows us to infer the amount of birefringence Δn at the level of 10(-8) and identify the orientation of the optical axes. The key benefit of this method is the ability to separately characterize each vacuum window, allowing the birefringence to be precisely compensated in existing vacuum apparatuses.
authors.affiliation: Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Steffen
authors.affiliation: Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Alt
authors.affiliation: Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Genske
authors.affiliation: Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Meschede
authors.affiliation: Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Robens
authors.affiliation: Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Alberti