Cyclops: A single beam 1.3 millimeter polarimeter

We present the design of a broad band, 1.3 mm polarimeter for astronomical observations and the results of first light observations at the Heinrich Hertz Telescope (HHT). The systematic polarization of the instrument plus telescope is 1.1%. The observed linear polarization of DR 21,P=1.65%±0.14% andθ=16°±2°, is consistent with previous measurements. Our 0.9% upper limit on the linear polarization of Cepheus A is the first 1.3 mm measurement reported. With Cyclops it is possible to map the magnetic fields in several of the brightest molecular cloud dust cores in the Milky Way. We comment on the expected performance of an achromatic Rexolite half-waveplate for λ=800μm to 1.3 mm.