Abstract: A scanning interferometer that is capable of measuring the complete relative movement of up to 10 or more measurement sites on a test structure, to determine thermal distortion or expansion. The interferometer includes means for dividing a source beam into signal and reference beams, and an acousto-optic deflector for deflecting the signal beam in response to a control signal to produce a deflected signal beam. The control signal is generated such that deflected signal beams are sequentially directed to the different measurement sites. Reflection means at each measurement site reflects the deflected signal beam to produce a reflected signal beam. Each reflected signal beam is combined with the reference beam to produce an interference pattern, and a photodetector positioned in the interference pattern produces a fringe signal. Signal processing means are provided for periodically measuring the phase of the fringe signal for each deflected signal beam, to thereby measure the movement of each measurement site.

Abstract: A filter and beam combiner is comprised of a small glass plate having a microscopic two sided elliptical mirror on one side thereof. The signal beam is spatially filtered on one side of the mirror and then directed to a target. On the other side of the mirror there is a compensating glass plate through which the reference beam passes, to correct for refraction relative to its passing through the first plate, before it enters the other glass plate and is directed onto said other side. The reference beam is spatially filtered by the mirror for combination with the signal beam, which returns from the target substantially enlarged by diffraction so as to pass around the mirror and through the plate to be combined with the reference beam.The signal beam is passed through acousto-optic modulator (AOM). The reference beam is passed through an 81 MHz AOM. The AOM's produce a doppler shift of the coherent light source frequency as the light is diffracted by a moving sound wave in the modulator.

Abstract: A shearing interferometer which includes a laser source, a reflector structure and an interference detection system. The reflector structure is mounted on an object, the angle of which, relative to a reference line, is to be determined. The reflector structure includes a transmission hologram and a retroreflector, wherein the transmission hologram is so constructed and positioned relative to the retroreflector that two or more parallel beams of preselected separation (shear) are produced for each incident beam. The difference in optical path length of a given pair of the parallel beams will vary depending on the object angle, and hence, the interference effect of the given pair of parallel beams will also vary in accordance with object angle. The interference effect is summed at a detector, and then analyzed by a tracking circuit to determine object angle.

Abstract: A modulated light beam is projected from a transmitter aircraft toward a receiver aircraft and reflected back toward the receiver aircraft by a retroreflector mounted on the receiver aircraft. The reflected light beam is received by the transmitter aircraft and is focused onto the face of an image dissector tube. The location of the reflected light beam on the face of the tube defines the position of the receiver aircraft in azimuth and elevation with respect to the position of the transmitter aircraft. The range difference between the two aircraft is determined by phase comparing the transmitted light beam with the received light beam. When used for in-flight refueling, further retroreflectors are mounted on a refueling boom and a similar technique is used to determine the exact location of the boom and its associated refueling nozzle.