Limits Due to Instrumental Polarisation in CMB Experiments at Microwave Wavelengths

Abstract

An extended analysis of some instrumental polarisation sources has been done, as a consequence of the renewed interest in extremely sensitive polarisation measurements stimulated by Cosmic Microwave Background experiments. The case of correlation polarimeters, being them more suitable than other configurations, has been studied in detail and the algorithm has been derived to calculate their intrinsic sensitivity limit due to device characteristics as well as to the operating environment. The atmosphere emission, even though totally unpolarised, has been recognized to be the most important source of sensitivity degradation for ground based experiments. This happens through receiver component losses (mainly in the OMT), which generate instrumental polarisation in genuinely uncorrelated signals. The relevant result is that, also in best conditions (cfr. Antarctica), integration times longer than ~40s are not allowed on ground without modulation techniques. Finally, basic rules to estimate the maximum modulation period for each instrumental configuration have been provided.

20 pages, 5 postscript figures. Accepted for publication in New Astronomy (see http://www.elsevier.nl/locate/newast)

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• Systematic effects in the measurement of polarization by the PLANCK telescope
• Constraining the reionization history with large angle CMB polarization
• Astronomical Receiver Modelling Using Scattering Matrices
• Systematic effects induced by a flat isotropic dielectric slab
• Effects of Thermal Fluctuations in the SPOrt Experiment
• The BaR-SPOrt Experiment