Laser doppler velocimeter

Claim 1

A laser Doppler velocimeter for measuring the velocity of a target, comprising: a) a laser producing a laser beam, b) a beam splitting means for splitting said laser beam into a probe beam and a reference beam said probe beam being directed at said target, c) a collection-forming means for collecting light of said probe beam reflected from said target and forming at least a portion of said reflected light into a reflected beam, d) a directing means for directing both said reference beam and said reflected beam into at least one atomic line filter said atomic fine filter comprising: 1) a vapor cell, 2) a first magnet means for providing a constant magnetic field at said vapor cell, 3) a second magnet means for providing an alternating magnetic field at said vapor cell, said alternating magnetic field defining a first frequency, 4) crossed polarizers, e) a detection means for detecting light of said reference beam and said reflected beam passing through said at least one atomic line filter, said reflected light detected by said detection means containing light oscillating at said first frequency and oscillating at a second frequency equal to twice said first frequency and said reference beam containing light modulated at a frequency equal to twice said first frequency, said first and said second frequencies each defining amplitudes, f) a frequency measuring means for measuring the relative amplitudes of said first and said second frequencies in the light detected by said detection means, the velocity of said target being determinable from said amplitude measurements.