A 350 Micron Array Polarimeter Using Translational Modulators

We describe a polarimeter that will be a testbed for a novel polarization modulator. This modulator is composed of two modified Martin-Puplett interferometers in which the input polarization state is transformed by adjusting the phase delays between linear orthogonal polarizations in each of the two stages. This type of modulator represents a potential improvement over existing technology in the following three ways. First, these modulators can fully characterize the polarization state by measuring Stokes Q, U , and V . The characterization of V is especially useful as a diagnostic for systematic errors. Second, the Martin-Puplett modulators can be easily retuned to observe at multiple frequencies. Finally, the small translations required for modulation can be accomplished with fewer moving parts than the rotational motions in wave plate modulators, thus potentially leading to modulators with longer lifetimes than those currently employed in polarimeters. The next generation of polarimeters, designed for both the study of Galactic magnetic fields in the far-infrared and submillimeter and the measurement of the polarized component of the Cosmic Microwave Background, will need to incorporate modulators with these attributes. This prototype polarimeter will be a modified version of the Hertz polarimeter that had until recently been operating on the Caltech Submillimeter Observatory. After modification, Hertz will be moved to the Heinrich Hertz Telescope in Arizona. We will utilize dynamic scheduling to efficiently observe during the best fraction of weather at this site.

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