30 May 2003 Difference displacement measurement using digital holograms as coherent masks
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The rapid development of spatial light modulators in the past few years opened an exciting new area in coherent optical metrology. Commercially available liquid crystal spatial light modulators (LC SLM's) are capable to optically reconstruct digital holograms in quite good quality, so the reconstructed real image of an object can be used as a coherent illuminating mask in optical measurement methods like digital holography (DH) or Electronic Speckle Pattern Interferometry (ESPI). In our work we present experimental results of measuring the difference and sum of two displacements of an object pair (master and test object) using these two techniques. We describe the measurement setups in a DH and an ESPI arrangement, which are capable to project the real image of the master object -- using its previously recorded digital holograms in the SLM device -- onto the test object. If two digital holograms, recorded before and after the deformation of the master object, are used to illuminate the test object in its initial and deformed state, four images can be recorded either in the DH setup or in the ESPI setup. Using these four-four images, the contour fringes of the difference and sum of the master and test object displacements can be calculated. In the case of DH, these images are digital holograms, which are subject to numerical reconstruction, and in the case of ESPI the four images are plain speckled images, which can be used to obtain ESPI fringes (correlograms). As a result, we present several fringe images of our object pair made with these two methods.
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Balazs Gombkoto, Balazs Gombkoto, Janos Kornis, Janos Kornis, Zoltan Fuzessy, Zoltan Fuzessy, Tamas Rozsa, Tamas Rozsa, } "Difference displacement measurement using digital holograms as coherent masks", Proc. SPIE 5144, Optical Measurement Systems for Industrial Inspection III, (30 May 2003); doi: 10.1117/12.499794; https://doi.org/10.1117/12.499794

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