Recent Applications of Coherent Optics in Aerospace Research

Abstract

The Royal Aircraft Establishment has an extensive programme of work on the application of coherent optical methods to problems arising in aerospace research. In addition to the use of both real-time and double-pulse holographic interferometry in the non-destructive testing of experimental aircraft components, techniques have been developed for the investigation of the mechanical properties of new composite materials and for studies of the behaviour of these and of more conventional materials under stress. Results obtained using a moire-type method for the determination of in-plane strain are presented; and an interferometric system is described which, incorporates an image-converter camera for study ing the surface deformation of a metal bar during the passage of a shockwave front. A simple interferometric method is being applied to the measurement of vibration amplitudes in the subnanometer range; some typical results showing the behaviour of a piezo-electric transducer at frequencies up to 1 megahertz are given. Current work in connection with aerial photography is described, including the incorporation of holographic optical elements into a very large Fizeau interferoscope being constructed for the examination of aircraft camera window. Laser anemometry techniques for supersonic wind tunnel applications using an argon laser and a photon-correlator have been developed. Results obtained in laminar and turbulent air flows at transonic and higher Mach numbers are discussed.