A laser Doppler velocimeter has been developed that uses two of the colors emitted from an argon-ion laser for the simultaneous measurement of orthogonal velocities. Designed for use in a 2.13-m by 3.05-m wind tunnel, it is capable of traversing its focal volume across spatially unstable flows at scan speeds of up to 1.5 m/sec. Its optical layout and principles of operation are discussed, and the data from a typical traversal of a trailing wing-tip vortex are presented.

Maximum quantum efficiencies attainable with commercially available semitransparent photocathodes are near 30% (for blue light). Work in the Instrumentation Division at Ames Research Center, NASA, has achieved quantum efficiencies as high as 58% with these same photocathodes through the use of optical enhancement. Improvement ratios in the red and near ir are even larger, but of course, the original sensitivities are smaller at these wavelengths. In addition to simply improving sensitivity, effort is also directed toward extending the applicability of the technique. A new class of devices recently conceived at Ames Research Center will allow application of optical enhancement to TV camera tubes, image intensifiers, and other imaging detectors. This paper describes the optical enhancement work in detail with major emphasis on results in the areas mentioned above.

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