Abstract

The principle of directional sensing in laser Doppler velocimetry is to measure the Doppler shift relative to an offset frequency whereby the sign of the velocity component is determined. Introducing this offset frequency is usually done by using a Bragg cell to shift the frequency of one of the two laser beams in the velocimeter. To avoid this bulk optic component other techniques based on frequency modulation of the field from a laser diode by applying a modulation to its drive current may be used. Especially one method using a sawtooth modulation scheme has been shown to succesfully produce the desired optical frequency difference when the modulated optical field is split into two fields propagating along paths of different lengts.¹

© 1986 Optical Society of America