Many materials and fabrics fluoresce, meaning they shine after irradiation with light, especially UV light. With this method, it is possible to detect fluorescing substances with an extremely high degree of sensitivity. Since many functional coatings, but also impurities, have a characteristic intrinsic fluorescence, they can be detected by fluorescence analysis.
To use fluorescence in metrology, a light source, such as a laser or an LED, must be directed onto the object, which then emits light at a wavelength longer than that of the light source. Optical filters separate the fluorescent light from the excitation light. Cameras or photomultipliers are used for detection. In addition to the pure detection of organic contaminants on surfaces, the evaluation of the spectra is very informative, since in some cases it is possible to differentiate substances based on the spectra.
Fluorescence measurement during production
In production, the use of fluorescence measurement technology for the inspection of surfaces in terms of quality monitoring is of great importance. For example, it must be ensured that surfaces are free from contamination before coating or painting. Components must be checked for cleanness and medical devices for purity and sterility before assembly. Last but not least, the usability of a product often depends on adherence to the purity requirements during manufacture.
Fraunhofer IPM develops highly sensitive, imaging fluorescence measuring systems for very different applications. Examples include the 100 percent check of oiled sheets and the purity control of metal components prior to welding, soldering or gluing. In addition, this technique can be used to test transparent, organic coatings for completeness and thickness. Due to the high measurement and evaluation speed, the systems can be used directly in the production line. Mechanics, optics, electronics, software and interfaces are customized.
Use of camera technology and laser scanners
Small objects up to a few 100 cm² are examined with high resolution using the F-Camera system. This system enables high-resolution imaging, in which fluorescence - including in combination with other imaging procedures - generates very meaningful image data. Since test specimens are sometimes so large that they can not be inspected quickly enough with a camera-based fluorescence measuring system, the F-Scanner was used to develop an alternative system based on a laser scanner. The component is scanned with a UV laser whose beam is deflected two-dimensionally via a scanner mirror. A sensitive photodiode records the previously spectrally filtered fluorescent light. With a specially developed software, the image of the specimen is assembled and superimposed with the fluorescence information.