Rapid velocity sensor using a static confocal Fabry-Perot and a single frequency argon laser

The technique of laser anemometry based on direct optical frequency measurement has recently been successfully used to investigate supersonic two phase flow where the time averaged velocity spectrum was recorded. The present work proposes two systems which extend the technique to 'instantaneous' velocity measurement, such a system could be adopted for use in any experimental situation where it is desired to record rapid fluctuations in an optical frequency.