1 mm Dual-polarization science with CARMA

We have constructed dual polarization 1 mm receivers for the CARMA array. A key science goal for these receivers is to map the linearly polarized thermal emission from dust grains in interstellar clouds, which may be used to infer the magnetic-field morphologies in these regions. Polarization fractions of a few percent are typical of this radiation. For an aperture synthesis array like CARMA it is advantageous to measure this weak linear polarization by cross-correlating the signals from circularly polarized feeds. To observe circular polarization, we install a waveguide polarizer between the feed horn and the OMT (orthomode transducer), at a temperature of 4 K, to convert incoming circularly polarized signals into linearly polarized signals. The receivers use waveguide OMTs to split the incoming radiation into orthogonal linear polarizations. The two OMT outputs are coupled to separate SIS (superconductor-insulator-superconductor) mixers and WBA-13 LNAs (low-noise amplifiers).