SHARP: the SHARC-II polarimeter for CSO

Abstract

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. This camera can be operated at either 350 or 450 microns. We developed a module that is installed at the CSO Nasmyth focus in order to convert SHARC-II into a sensitive imaging polarimeter, which we refer to as "SHARP". SHARP splits the incident beam into two orthogonally polarized beams that are then re-imaged onto different halves of the SHARC-II bolometer array. When this removable polarimetry module is in use, SHARC-II becomes a dual-beam 12 x 12 pixel polarimeter. Sky noise is a significant source of error for submillimeter continuum observations. Because SHARP simultaneously observes two orthogonal polarization components, we are able to eliminate or greatly reduce this source of error. Here we describe the design of SHARP and report preliminary results of tests and observations carried out during our first two runs at CSO

Design and initial performance of SHARP, a polarimeter for the SHARC-II camera at the Caltech Submillimeter Observatory

“…By making a judicious choice for the location of the final focus fЈ, we eliminate the need to move any component of the SHARC-II system when installing SHARP (see Subsection 2.C). The focus of the first mirror is placed on f, and f is reimaged at fЈ, the focus of the second paraboloid, with minimal aberration [26]. All the polarimetry components are installed after P1.…”

“…The left view shows this reconstituted image being directed into the relay optics by flats F4 and F5. P1 and P2h (or P2v) form a pair of crossed paraboloids [26]. SHARC-II is easily converted back to photometric mode by removing P1 and F5 (Box 4; see Two important elements of the reimaging design are that the angles of incidence at the two paraboloids are identical, and that the pupil is located approximately halfway between the two paraboloids [27].…”

“…In previous papers we described an early version of the optical design [25], and our firstlight tests [26]. Initial scientific results will be described in future papers.…”

“…In this paper we describe the optical design of SHARP (section 2) and present results of tests carried out during the first 18 months of operation at CSO (section 3). In previous papers we described an early version of the optical design 24 , and our first-light tests 25 . Initial scientific results will be described in future papers.…”

Angular and polarization response of multimode sensors with resistive-grid absorbers

“…1, S2) [17][18][19][20]. Multimoded sensors for imaging have also achieved polarization sensitivity through a wire-grid analyzer [21][22][23][24] (Fig. 1, M1 and MP1).…”