Abstract: An electrooptical sensor system directly measures the angle between two nearly parallel collimated laser beams. After focussing with a positive lens, the beams pass through a photoelastic modulator, a quarter wave retardation plate, and two polarizers. The beams then hit a lateral cell position sensor. Electrical signals from the lateral cell are processed with special electronics to yield a voltage which is proportional to the angular difference between the two beams. The sensor measures extremely small angles and operates at a high bandwidth. Its primary application is in the control of phased array optical telescopes.

Abstract: An apparatus and technique are described for phasing the outputs of a multiplier telescope array used as a laser transmitter. The technique uses samples of the transmitted beams to control optical path lengths through the separate telescopes so that the beams add coherently at the receiver. The phasing concept is applicable both to systems which provide inputs to the multiple telescopes by dividing a single laser beam and to systems in which the inputs to the telescopes and multiple, phase-locked laser beams. The approach is also compatible with single line and multi-line lasers, and it does not entail stringent alignment requirements. The concept uses a procedure to find the zero optical path difference condition and to effect fine control of the optical path lengths through the different telescopes. Algorithms are described for estimating the phase mismatch from focal plane measurements.