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Laser speckle photometry - Optical sensor systems for condition and process monitoring

: Chen, Lili; Cikalova, Ulana; Bendjus, Beatrice; Gommlich, Andreas; Sudip, Shohag Roy; Schott, Carolin; Steingroewer, Juliane; Belting, Matthias; Kleszczynski, Stefan


MP materials testing 61 (2019), Nr.3, S.213-219
ISSN: 0025-5300
Fraunhofer IKTS ()
Laser-Speckle-Photometry; Process monitoring; defect-monitoring; build-up welding; Additive manufacturing; Biomass

Laser speckle photometry (LSP) is an innovative, non-destructive monitoring technique based on the detection and analysis of thermally or mechanically activated speckle dynamics in a non-stationary optical field. With the development of speckle theories, it has been found that speckle patterns carry information about surface characteristics. Therefore, LSP offers a great potential for the characterization of material properties and monitoring of manufacturing processes. In contrast to the speckle interferometry method, LSP is very simple and robust. The sample is illuminated by only one laser beam to generate a speckle pattern on the surface. The signals obtained are directly recorded by a CCD or CMOS camera. By appropriate optical solutions for the beam path, typically, resolutions of less than 10 mu m are reached if larger areas are illuminated. LSP is definitely a contactless, quick and quality relevant material characterization and defect detection method, allowing process monitoring in many industrial fields. Examples from online biotechnological monitoring and laser based manufacturing demonstrate further potentials of the method for process monitoring and controlling.