New intensity and visibility aspects of a double-loop neutron interferometer

Various phase shifters and absorbers can be put into the arms of a double-loop neutron interferometer. The mean intensity levels of the forward and diffracted beams behind an empty four-plate interferometer of this type have been calculated. It is shown that the intensities in the forward and diffracted directions can be made equal using certain absorbers. In this case the interferometer can be regarded as a 50/50 beam splitter. Furthermore, the visibilities of single- and double-loop interferometers are compared to each other by varying the transmission in the first loop using different absorbers. It can be shown that the visibility becomes exactly unity using a phase shifter in the second loop. In this case the phase shifter in the second loop must be strongly correlated to the transmission coefficient of the absorber in the first loop. Using such a device homodyne-like measurements of very weak signals should become possible.