A Polarimetry Module for CSO/SHARC-II

The Submillimeter High Angular Resolution Camera II (SHARC-II) is a 32 x 12 pixel submillimeter camera that is used with the ten-meter diameter Caltech Submillimeter Observatory (CSO) on Mauna Kea. SHARC-II can be operated at either 350 or 450 microns. We are developing an optics module that we will install at a position between the SHARC-II camera and the focus of the CSO's secondary mirror. With our module installed, SHARC-II will be converted into a sensitive imaging polarimeter. The basic idea is that the module will split the incident beam coming from the secondary into two orthogonally polarized beams which are then re-imaged onto opposite ends of the “long and skinny” SHARCII bolometer array. When this removable polarimetry module is in use, SHARC-II becomes a dual-polarization 12 x 12 pixel polarimeter. (The central 12 x 8 pixels of the SHARC-II array will remain unused.) Sky noise is a significant source of error for submillimeter continuum observations. Because our polarimetry module will allow simultaneous observation of two orthogonal polarization components, we will be able to eliminate or greatly reduce this source of error. Our optical design will include a rotating half-wave plate as well as a cold load to terminate the unused polarization components.