Theory of the resonant filter for polarized radiation

A technique of the resonant filtering is used in the Mössbauer spectroscopy for receiving polarized radiation. Two main contributions suppressing the filter quality are revealed. The first contribution results from unwanted small absorption located at the resonance energy. The second one is caused by large, unwanted absorption located far from the resonance energy. It is shown that both contributions can be parametrized by a small parameter r; the effective thickness is proportional to 1/r2, while the departure of the maximum polarization degree from the unity is proportional to r. The properties of the filters constructed so far for linear and for circular polarization are discussed within the presented approach.