Development of shearographic imaging system

Since the submission of the First Periodic Report no significant progress in these laboratories was made until the delivery of a 50 mW. helium-neon laser from Spectra Physics together with a spatial filtering unit. The present report gives details of the adopted experimental arrangements and also includes photographs of the shearographic fringes obtained for a number of displacements of a stainless steel sample. The basic arrangement for image shearing is shown in schematic form. In our arrangement the 1 degree optical wedge covering half the field was mounted in the filter-holder of a Toyo-View Model 45E Plate camera fitted with a 150 mm. f5.6 compound lens. The test samples employed in the present work were stainless steel discs of 0.15mm. thickness and 80 mm. diameter. One surface of the disc was sprayed matt white using a cellulose-based can of automobile touch-up paint in order to increase the reflectivity of the sample surface. Also drawn on this white surface were two fine intersecting lines, one in the horizontal plane and the other in the vertical plane. The sample was mounted on a block of aluminum which had a central cut-out through a point force could be applied.