An efficient phase-shifting scheme for bolometricadditive interferometry

摘要

Context. Most upcoming CMB polarization experiments will use direct imaging to search for primordial gravitational waves throughthe B-modes. Bolometric interferometry is an appealing alternative to direct imaging that combines the advantages of interferometryin terms of systematic effects handling and those of bolometric detectors in terms of sensitivity.Aims. We calculate the signal from a bolometric interferometer in order to investigate its sensitivity to the Stokes parameters payingparticular attention to the choice of the phase shifting scheme applied to the input channels in order to modulate the signal.Methods. The signal is expressed as a linear combination of the Stokes parameter visibilities whose coefficients are functions of thephase shifts.Results. We show that the signal to noise ratio on the reconstructed visibilities can be maximized provided the fact that the phaseshifting scheme is chosen in a particular way called "coherent summation of equivalent baselines". As a result, a bolometric interfer-ometer is competitive with an imager having the same number of horns, but only if the coherent summation of equivalent baselinesis performed. We confirm our calculations using a Monte-Carlo simulation. We also discuss the impact of the uncertainties on therelative calibration between bolometers and propose a way to avoid this systematic effect.