A Traveling Michelson Interferometer with Phase-Locked Fringe Interpolation

The advent of single-mode cw dye lasers and their application to Doppler-free spectroscopy makes essential the capability of rapidly measuring the dye laser s wavelength with sub-Doppler absolute accuracy. Our wavelength measuring apparatus [1] is basically an automatic-scanning Michelson interferometer utilizing corner-cube retroreflectors, with phase multiplication for extending the resolution. The interferometer measures an unknown wavelength in terms of a reference laser wavelength. Motion of the carriage holding the corner-cubes lengthens one arm and shortens the other arm of this interferometer. For a given distance traveled by the carriage, a different number of fringes will be counted for the unknown laser and the reference laser (since their wavelengths are different). Naturally, a higher resolution level for the measured wavelength will require a longer travel, and consequently, a longer measuring time. Our resolution-extension concept, however, enables us to obtain wavelength information of a given resolution level in 100-fold less time than is required with direct fringe counting.