Laser doppler velocimeter detector

Claim 1

A balanced detector for a laser doppler velocimeter comprising means for generating a single laser beam for utilization in determining velocity information in flow fields, means to split said single laser beam into first and second equally intense beams, means to rotate the plane of polarization of said first beam 90* to provide a third beam, means to focus said second and third beam to cross over at a common point with light scattering out of the region of said common point, said scattered light being composed of two components with one beam having its plane of polarization rotated by 90*, means to collect said scattered light at a preselected position, polarization beam splitter means passing the collected light, said polarization beam splitter means rotating said passed collected light 45* operating to mix a portion of each oppositely polarized beam to produce doppler information in the form of fourth and fifth beams, first and second phototube means detecting said fourth and fifth beams to provide first and second electrical signals, respectively, means to invert electrically said first electrical signals to provide a third electrical signal, and means to add said second and third electrical signal to produce only the frequency content of said doppler information.