Abstract: A shearogram representing an object and including a fringe pattern arising from a change in local surface strain brought about by an applied stress during the making of the shearogram is reconstructed by a special viewer. The viewer holds the shearogram transparency adjacent to a focusing lens having an optical axis, and projects off-axis white light through the lens and transparency to a focal plane where the resulting diffraction pattern is viewed directly on a screen or by a video camera and display monitor. By projecting the light from different positions around the axis a first position can be found which tunes the diffraction efficiency to an optimum for the best view of fringe patterns and a second position can be found which eliminates the fringe patterns and shows only a photographic image of the object. The light source is a rotatable disk with two apertures containing light diffusing elements which are illuminated by a lamp. The disk is rotated to change the projection angle.

Abstract: Method and apparatus for analyzing the deformation of an object resulting from the application of stress. A novel optical element is used to perform shearometric analysis upon a test object. The novel optical element has an overall pattern of first and second pluralities of regions having significantly different indices of transmissivity. The pattern of variations causes pairs of light rays which are reflected from two distinct points on the test object at a divergent angle to emerge from the optical element so that they are nearly parallel. The nearly parallel rays are then received upon a photoelectrical sensing means such as a video camera or photoelectric array. Because the rays impinging thereon are nearly parallel, they may be adequately resolved by the photoelectric sensing means, thus enabling shearometric analysis to be performed electronically in a rapid and cost-effective manner.

Abstract: The present invention relates to a test block for use with interferometric analysis apperatus which simulates defects of known dimension in a test object. The known defects created by cavities in the test block which is positioned within the interferometric analysis apparatus test chamber for analysis to determine whether the apparatus is properly calibrated. The cavities have a predetermined geometry and location within the test block which control flexure of a sheet of flexible material associated with the test block. The predetermined flexure can be correctly detected only by a properly calibrated interferometric device. The test block provides for a vent line to communicate with the cavities when the test block is placed inside a vacuum chamber associated with the interferometric analysis device to allow a pressure differential to create the forces for the predetermined fixture.

Abstract: In order to detect subsurface defects in a vehicle tire the tire is placed in a sealed pressure chamber and the pressure is rapidly reduced to a very low level, and maintained at that level for a period of time. The body of the tire creeps for a period of time following the pressure change as a result of the stresses imposed by the pressure change. During this creep period a section on the surface of the tire is illuminated with coherent light and two separate exposures of interferograms are made using the reflected light and recorded on either a photographic media or the cathode of a television image tube. The exposure may either be holographic, in which case the interferogram is produced by using a reference beam of light derived from the same source that illuminates the object surface, or shearography, in which case two focused images of the tire surface section are formed on the photosensitive media, displaced with respect to one another and overlapping one another.

Abstract: A method and apparatus for measuring strains in a test object in any of a plurality of directions. The object is illuminated with coherent light so that light is reflected to a focussing lens and a shearing diffraction grating having lines extending in a plurality of directions. The various diffracted orders interfere at the focal plane of the lens and are recorded on a photographic media. The object is then stressed and a second exposure is made on the same media, resulting in interference between the fringes produced on the two exposures. The media is developed as a transparency and subjected to optical processing to detect strain in any direction.

Abstract: For purposes of eye examination, a method is provided for determining the presence or absence of structural anomaly in the retina. In this method, the surface of the retina (under zero stress or any one of a selected variety of stress conditions to produce deformation) is illuminated with coherent light and separate exposures or interferograms are made using the reflected light and recorded either photographically or electronically such as by storage or display via the cathode of a television image tube. The exposure may either be holographic, in which case the interferogram is produced by using a reference beam of light derived from the same source that illuminates the object surface, or shearographic, in which case two focused images of the retinal surface section are formed on a photosensitive medium, displaced with respect to one another and overlapping one another.

Abstract: A machine for performing double exposure, interferometric analysis of the changes in an object surface that result from changes in the ambient pressure on the object, as by holography, includes a pressure chamber partially formed by a horizontal base operative to support the test object and interferometric camera on its upper surface. A semispherical pressure dome is placed on the base over the test object and camera. A manifold volume bounded by a thin resilient steel disc supported beneath the base plate on a rubber gasket has its pressure equalized with the area beneath the dome by passages formed beneath the base plate. When the pressure is changed beneath the dome a similar pressure change occurs in the manifold volume beneath the base so that no net pressure forces are exerted on the base plate and no deformation of the camera or test object occurs.

Abstract: To obtain a photographic record of an object surface having superimposed interference fringes arrayed as a function of the deformation which results in the object from an applied stress, which may be mechanical, thermal, or the like, the object is first illuminated with coherent light. The illuminated surface is then photographed with a camera having an optical wedge disposed over half of its lens to record two slightly displaced overlapping images of the object on the camera film. The object is then stressed by changing the ambient temperature or pressure or other mechanical loading, and the undeveloped film is exposed to a second set of overlapping images. The developed photograph contains a set of equal amplitude fringes representing the interference pattern between the two fringe sets generated by the two exposures and arrayed as a function of the strain in the object as a result of the stress.

Abstract: To form a hologram of a section of an object surface one end of each of a pair of elongated, flexible, optical fibers is illuminated with a laser beam through an optical mechanism which allows adjustment of the amount of light that falls on each of the fiber ends. The opposite end of one of the fibers is disposed adjacent to the object of which the hologram is to be formed so that the light output of that fiber diffuses and illuminates the relevant surface. A photographic plate is disposed to receive light reflected from the object surface as well as a reference beam radiating from the output end of the other fiber. A photodetector device receives a portion of the reference beam at one input and a portion of the object beam at another input and provides a visual indication of the relative intensity of the beams. The input to the fiber elements is adjusted to achieve the desired beam ratio for forming a hologram.