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Design and development of an oblique incidence interferometer Bajaj, Vijay Kumar

Abstract

Interferometry offers great scope in the study of surface topography and small surface displacements. The fundamentals of surface as encountered in engineering practice and a few of the optical methods available for the metrology of surface have been reviewed. In particular, Oblique Incidence Interferometry has been developed in detail for the study of relatively rough surfaces. The relationship between this method and the recent and more general method of holography has been explained. Some preliminary experiments were conducted to gain a feeling for the latter two methods and an oblique incidence interferometer was designed, constructed, and tested for its suitability for measuring industrial surfaces of approximately 22 inches in span from the following aspects: 1. The determination of surface topography of rough surfaces; 2. The measurement of small surface displacements; 3. The execution of forward scatter and back scatter holography for normal qualitative recording and subsequent comparison—holographic interferometry. A rough turned surface of a 12 inch diameter circular aluminium plate was examined. Small surface displacements of the same plate were measured and compared with theoretical predictions. Further holographic interferometry was performed on a turbine blade. Some of the difficulties encountered, such as the significance of diffraction effects at edges and marks on the surface and the determination of scale were studied and are discussed. Future studies on tubes and cylinders are discussed.

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