A laser-Doppler velocimeter, for measuring the velocity of particles passing a test location, comprises first and second lasers for providing a measurement laser beam directed along a first axis and a guide laser beam that is parallel to the measurement beam. The guide beam and the measurement beam are...http://www.google.com/patents/US4818101?utm_source=gb-gplus-sharePatent US4818101 - Laser-doppler velocimetry
