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Holographic Interferometry
Published in Raymond K. Kostuk, Holography, 2019
Holographic interferometry is a method of comparing optical fields that are transmitted or reflected from an object. One or both of the waves used in forming the interference pattern are produced by the hologram. It is a non-contact, non-destructive technique for measuring changes in the optical path length that occur when the physical properties of the object are altered in some way. Changes in the optical path length indicate variations to the thickness, surface topography, refractive index, or any combination of these parameters. Since changes in optical path length as small as 1/100th of the wavelength can be detected, the technique is very useful for sensing small changes or perturbations of a test object. The high sensitivity of the process places some restrictions on the total change in phase that can be measured. In addition, since this is an interferometric process, the temporal and spatial coherence properties of the light must be sufficient for the geometry of the setup. Nevertheless, the technique has proven very valuable for non-destructive testing of components and in manufacturing.
Optical Holographic Imaging
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
Double exposure holographic interferometry is a variant on the vibration method. A hologram is made of a stationary object. The object is then distorted, perhaps by the application of pressure. A second hologram is recorded on the same recording medium. The reconstruction process produces two superimposed images, one of the object before the distortion and one after. The two images combine interferometrically, producing again a fringe pattern which is dark where the images are out of phase and bright where they are in phase. This form of holographic interferometry is useful, for example, for studying the response of a rigid object to various applied stresses.
Holography
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
More generally, holographic interferometry uses the interference produced between either an object and a hologram, or two holograms. An example of a setup is presented in Figure 8.35. A hologram with a wavefront similar to the object has been recorded. It is then replayed with a reading beam, and the diffraction is superimposed with the object beam going through the hologram. If the object is deformed between recording and replaying, the deformation is visible through the fringe pattern Figure 8.36[45].
Wigner–Ville distribution based diffraction phase microscopy for non-destructive testing
Published in Journal of Modern Optics, 2019
Ankur Vishnoi, Ajithaprasad Sreeprasad, Gannavarpu Rajshekhar
Optical interferometric techniques such as electronic speckle pattern interferometry (1, 2), shearography (3) and digital holographic interferometry (4) have been extensively used for non-destructive metrology in diverse areas such as experimental mechanics, material science, biomechanics and precision engineering. These techniques operate by encoding the measurand information in a fringe pattern, and require a fringe demodulation or analysis (5) method to retrieve the desired information. An important problem in this domain is reliable extraction of phase derivatives from a fringe pattern, which has several practical applications. In electronic speckle pattern interferometry, phase derivatives have been applied for measuring slopes (6) and strain (7, 8), and for dynamic deformation analysis (9). Similarly, there are several applications of digital holographic interferometry involving the use of phase derivatives such as strain, curvature and twist measurements (10–12) and defect identification (13, 14). Compared to the aforementioned techniques, shearography is an optical technique where the influence of the spatial derivative is significantly evident since the experimental setup is designed such that the resulting fringe pattern directly maps the derivative information due to the interference of the wave scattered from the test specimen and its sheared or spatially shifted counterpart generated by a shearing element such as wedge prism (15). Additionally, shearography eliminates the need for a separate reference arm for interference, and is resistant to vibrations. These elegant properties have enabled widespread use of shearography for non-destructive evaluation (15), material characterization (16), leak detection (17) and residual stress analysis (18). However, fringe processing accuracy in shearography is strongly affected by the presence of shearing introduced in the experimental setup and the performance is also sensitive to noise.