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A number of photomultiplier tubes have been assessed for application in experiments where the counting of individual photoelectrons from the photocathode is necessary or advantageous. Pulse height distributions, signal-to-noise-in-signal ratios, over-all quantum-counting efficiencies, time dependent statistical correlations, and dark current properties have been investigated and compared with theoretical expectations. Amajor finding has been the general low value of over-all quantum-counting efficiency. Direct measurements of this figure have not, to our knowledge, been published previously. A second conclusion has been that, although there seems to be no reason why high performance with respect to each of the features considered should not be achieved in a single tube, we have not yet found one in which this is so.

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A detailed comparison of experimental and theoretical SNR in an IR laser heterodyne system has been made with three different signal analyzers. Good agreement, considerably better than a factor of 1.5, is reported. Accurate allowance was made for transmission in the receiver optics, the effective quantum efficiency of the detector due to shot noise domination by the local oscillator, and for coherent speckle effects across the collection aperture. The evaluation of SNR with a surface acoustic wave spectrum analyzer and digital integrator is described in some detail. As an illustration an absolute measurement of backscattering strength in the atmosphere from an airborne equipment at altitudes up to 13.1 km is provided.

A novel integrated optic approach to the design and manufacture of an optical subsystem for a Range-Doppler imaging lidar is described and demonstrated. The approach uses hollow waveguides to guide light between system components which are integrated into a common substrate. The design, manufacture and operation of an eleven element subsystem which is compact, rugged and provides coherent mixing efficiencies in excess of 800/0 of the theoretical maximum, are discussed. The results of trials of the subsystem at the Army Missile Optical Range (AMOR), involving measurements of Range-Doppler images of representative targets are described.