HETERODYNE LASER TRACKING AT HIGH DOPPLER RATES

A design is described for a transmitter/receiver system that may be us ed in a spaceborne laser heterodyne tracking system to produce a high- precision interferometer. We present a two-color laser scheme that ena bles accurate phase measurement even in the presence of a large Dopple r offset between the incoming and outgoing signals. The beat note betw een the two lasers provides a built-in frequency reference, while the delay line produced by the travel time of the tracking signal provides a stable self-comparison that measures drift in the frequency referen ce so that it may be corrected for. The resulting noise in the link is only the residual laser phase jitter and the shot noise in the phase measurement.