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Phase-Reference beam Profile Sensor (2REF-LDA)

By placing two photodiodes into one beam of a cross beam LDA one also gets a profile sensor. For a better mapping the receivers and their associated measuring volumes as well as their signals are painted green and red although the real beam colour is a single one. Depending on the trajectory of the scatterer the signals exhibit different phase relations. From the phase difference, the velocity and the geometry of the set-up the location of passage on the optical axis of the beams can be calculated. An advantage of this configuration is the use of only one beam for the receiver.