GB1261186A - Improvements in or relating to holographic methods of measurement - Google Patents

Abstract

1,261,186. Utilizing holography. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Dec.11, 1969 [Sept. 20, 1968], No.44938/68. Heading G2J. The amplitude and/or direction of an unknown motion at at least one point on the surface of a moving object is determined by:- (a) making three holograms or pairs of holograms of the surface including the point to provide live or frozen interference fringes on reconstruction corresponding to known displacements of the point in each of three known orthogonal directions 1, 2, 3 by known amplitudes; (b) observing said point in reconstructions of said holograms from at least three viewpoints 1 v , 2 v , 3 v in the planes of the holograms and determining the order of the live or frozen fringes produced at said point by each known displacement from each viewpoint; (c) calculating as constants the direction cosines of the measured direction of motion (defined) and the sensitivity factor (defined) for each viewpoint, said three viewpoints being chosen so that said measured directions of motion 1 s , 2 s , 3 s are not coplanar; (d) making a further hologram or pair of holograms of the surface to provide live or frozen fringes on reconstruction corresponding to the unknown motion; (e) observing in said reconstruction the point on the surface whose unknown motion is to be determined, determining the fringe order due to the unknown motion at said point from each of the three viewpoints; and (f) using the calculated constants to calculate the amplitude and/or direction of the unknown motion. The known displacements in the three known orthogonal directions may be translational or rotational. The measured direction of motion is defined as the vector bisecting the angle subtended at the point on the surface by the source of illumination I and the given viewing point 1 v , 2 v or 3 v . The sensitivity factor is half of this said angle. Preferably the holograms are recorded side-byside in strip form a set of four adjacent strips constituting a single viewpoint. The first three strips respectively being two superimposed holograms of each of the known displacements in the orthogonal displacements and the fourth strip being a single hologram of the vibrating object or two superimposed holograms of a distorted object. Desirably a continuous series of such groups are formed across a photographic plate subtending a large solid angle at the point of interest over the surface and thus giving a wide range of viewing points over the plate. One embodiment uses five viewing points, Fig.4 (not shown), three horizontally aligned lying in the common plane of the illuminating and viewing directions and the other two lying in a plane at right angles to the common plane of the first three.