Since the 1960s speckle patterns are used for the evaluation of quality-relevant material parameters and defects. The laser speckle photometry works without reference beam unlike other speckle-based processes. This allows for a simple and robust construction, which can be easily integrated into the process control. Measurement and calculation of the obtained data are performed in real time. Current research at IKTS focuses on in-line process monitoring, e.g. of additive processes, coating and biotechnological processes. This non-destructive test method is also suitable for many other applications in process monitoring and control.
The laser speckle photometry is based on the evaluation of the temporal change of speckle patterns, and offers the possibility to easily determine porosity and surface defects of various materials. A speckle pattern only becomes visible when a rough surface is illuminated by a coherent light source. In the process, a spatial structure with randomly distributed intensities is produced, which can be read out by a CMOS chip. If the test object is also thermally or mechanically stimulated, conclusions on material properties can be drawn from slightest changes of speckle patterns.
“The system developed at Fraunhofer IKTS consists of sensor, electronics, hardware, software and evaluation algorithmics. The modular design of the test method can be adapted to a variety of problems“ says Dr. Beatrice Bendjus, project manager at Fraunhofer IKTS. “In addition to geometric parameters, material parameters, such as porosity and hardness, voltage changes at the surface or specific process parameters can be non-destructively determined“ continues Bendjus. This new method has already proven itself in the laboratory and is now transferred to industrial application.