Laser Doppler Velocimetry by Backscatter Modulation of the Source

It is well known that small quantities of stray light reflected back into a laser cavity can produce large perturbations in the laser characteristics. To the best of our knowledge, however, no one has recognized that this effect can be used as a sensitive detection process for making Doppler velocity measurements. This technique has the added featurs that the critical beamsplitter alignment requirements of conventional laser Doppler velocimetry have been eliminated by eliminating the beamsplitter. We report here a demonstration using a CO2 laser and a rotating disk target.