Fully compensated Michelson interferometer of fixed-path difference.

A Michelson interferometer of fixed-path difference, capable of scanning over only one fringe, has been shown to be useful for the measurement of Doppler shifts from isolated emission lines. It is straightforward to field widen this type of configuration, but if different wavelengths are to be selected, the field widening must be achromatic. Further, for Doppler shift measurement, one requires a path difference that is highly stable with respect to temperature. The generalized requirements for meeting all these conditions are set out and a configuration that satisfies them is described. Sample characteristics are given for a number of different systems.