A precise real-time wavemeter

A wavemeter has been built utilizing a coincidence start/stop fringe counting technique with a standard, simple division-of-amplitude type interferometer. We utilize a microprocessor to control the counting and to calculate and display, in real time, the unknown wavelength and to indicate when the result is outside of a preset tolerance (e.g. mode hop). This system, utilizing the coincidence technique, gives an enhancement in the precision of at least a factor of 15 over standard fringe counting techniques.