title: Millimeter-wave achromatic half-wave plate.
abstract: We have constructed an achromatic half-wave plate (AHWP) suitable for the millimeter wavelength band. The AHWP was made from a stack of three sapphire a-cut birefringent plates with the opticalaxes of the middle plate rotated by 50.5 deg with respect to the aligned axes of the other plates. The measured modulation efficiency of the AHWP at 110 GHz was 96 +/- 1.5%. In contrast, the modulation efficiency of a single sapphire plate of the same thickness was 43 +/- 4%. Both results are in close agreement with theoretical predictions. The modulation efficiency of the AHWP was constant as a function of incidence angles between 0 and 15 deg. We discuss design parameters of an AHWP in the context of astrophysical broadband polarimetry at the millimeter wavelength band.
authors.affiliation: School of Physics and Astronomy, University of Minnesota, 116 Church Street, SE, Minneapolis, Minnesota 55455, USA. hanany@physics.umn.edu
authors.forename: Shaul
authors.initials: S
authors.lastname: Hanany
authors.forename: Johannes
authors.initials: J
authors.lastname: Hubmayr
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Johnson
authors.forename: Tomotake
authors.initials: T
authors.lastname: Matsumura
authors.forename: Paul
authors.initials: P
authors.lastname: Oxley
authors.forename: Matthew
authors.initials: M
authors.lastname: Thibodeau