POL-2: a Polarimeter for SCUBA-2

SCUBA-2 is a bolometer array camera for use at the James Clerk Maxwell Telescope (JCMT) and is currently under development in the UK, Canada, and the USA. This new instrument will work in two wavelength bands, 850 and 450 microns, and is currently scheduled to start operation in 2006. Here we present current options for a polarimeter, POL-2, that is being built for SCUBA-2. The polarimeter will have an achromatic continuously rotating half-wave plate in order to modulate the signal at a rate faster than atmospheric transparency fluctuations. Such a modulation should improve significantly the reliability and accuracy of sub-mm polarimetric measurements. The signal will be analyzed by a wire-grid polarizer. For calibration, a removable polarizer will also be available. The components, in the order that the radiation will encounter them, are the calibration polarizer, the rotating wave plate, and the polarizer. The components will be mounted in a box fixed permanently in front of the entrance window of the main cryostat of SCUBA-2. All components will be mounted so that they can be taken in and out of the beam remotely, making it very easy and fast to start doing polarimetry at the telescope. Software will be provided to control all the basic functions of the polarimeter. A data reduction pipeline capable of producing near publication quality results will be provided for both on-line and off-line reduction of polarimetric data. This polarimeter will be the most sensitive instrument for the detection of polarized radiation in the submillimetre regime. This will be possible by taking advantage of the extra sensitivity, imaging speed, and improved image fidelity of the new SCUBA-2 camera.