A polarization fabry-perot duochromator.

A two-channel Fabry-Perot interferometer for the measurement of very small displacements of spectral lines has been constructed. Advantage is taken both of the superior throughput and resolution of the Fabry-Perot. The two-channel operation is produced by the use of two concentric polarizers and a rotating analyzer. Application is made to the study of ion drifts in a Schüler hollow cathode plasma.