DEVELOPMENT OF THE MULTI-MODED PIXELS FOR THE LSPE/SWIPE FOCAL PLANE

The Large Scale Polarization Explorer (LSPE) is a balloon-borne telescope devoted to the measurement of Cosmic Microwave Background polarization at large angular scales, funded by the Italian Space Agency. SWIPE, its high frequency instrument, is a bolometric polarimeter operating in 3 bands, centered at 140, 220, and 240 GHz. Its optical design relies on multi-mode coupling in order to maximize photon collection efficiency, boosting per-pixel sensitivity under photon noise limited operation, at the price of unnecessary angular resolution. We describe the quasioptical system that couples the SWIPE detectors to the telescope through a multimoded antenna/waveguide/cavity assembly. Numerical simulations have been carried out to model the pixel response, both in intensity and polarization, and to forecast and optimize the final performance of the SWIPE detectors in CMB polarization measurements. Tests of pixel prototypes are being performed and an assessment of the final scientific performance for the full focal plane assembly is underway