K. Ishidoshiro, Y. Chinone, M. Hasegawa, M. Hazumi, M. Nagai, O. Tajima
We propose an innovative demodulation scheme for coherent detectors used in cosmic microwave background polarization experiments. Line removal of detector noise is one of the key requirements for the experiments. In experiments that use coherent detectors, a combination of modulation and demodulation is used to extract polarization signals as well as to suppress line noise. Traditional demodulation, which is based on the two- point numerical differentiation, works as a first-order high pass filter for such non-white noise. The proposed demodulation is based on the three-point numerical differentiation. It works as a second-order high pass filter. We evaluated its impact by applying it to data collected from a real coherent detector. Line noise is significantly suppressed as expected. We also found improvement of the noise floor in the demodulated data. This improvement results from minimization of 1/f noise contamination at around the modulation frequency.
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http://arxiv.org/abs/1203.2407
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