title: Achromatic half-wave plate for submillimeter instruments in cosmic microwave background astronomy: experimental characterization.
abstract: An achromatic half-wave plate (HWP) to be used in millimeter cosmic microwave background (CMB) polarization experiments has been designed, manufactured, and tested. The design is based on the 5-plates Pancharatnam recipe and it works in the frequency range 85-185 GHz. A model has been used to predict the transmission, reflection, absorption, and phase shift as a function of frequency. The HWP has been tested by using coherent radiation from a back-wave oscillator to investigate its modulation efficiency and with incoherent radiation from a polarizing Fourier transform spectrometer (FTS) to explore its frequency behavior. The FTS measurements have been fitted with an optical performance model which is in excellent agreement with the data. A detailed analysis of the data also allows a precise determination of the HWP fast and slow axes in the frequency band of operation. A list of the HWP performance characteristics is reported including estimates of its cross polarization.
authors.affiliation: University of Wales-Cardiff, UK. giampaolo.pisano@astro.cf.ac.uk
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Pisano
authors.forename: Giorgio
authors.initials: G
authors.lastname: Savini
authors.forename: Peter A R
authors.initials: PA
authors.lastname: Ade
authors.forename: Vic
authors.initials: V
authors.lastname: Haynes
authors.forename: Walter K
authors.initials: WK
authors.lastname: Gear