Measurement of surface displacement normal to the line of sight
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Two methods for measuring the displacement of a surface normal to the line of sight are described and experimental results presented. The displacement in either case may consist of a simple lateral or rotational shift of the body in total, or it may consist of small local displacements due to some type of mechanical stress. The displacement is displayed as a system of interference fringes over the image of the surface. The first method permits observation of the displacement fringes in real time; or, if a double exposure is recorded, the fringes can be observed directly on the doubly exposed photograph in white light. The second method requires spatial filtering of the image after recording a double exposure of the surface before and after displacement. However it permits selection of the component of displacement in any direction normal to the line of sight with a continuously variable sensitivity from the single (doubly exposed) transparency. Both methods are noncontacting, use only a single laser beam for illuminating the object and require no previously constructed grids or rulings.
KeywordsMechanical Engineer Laser Beam Fluid Dynamics Mechanical Stress White Light
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