Retro-Reflection Ellipsometry

Flat surfaces can be checked very well automatically by evaluating the reflection of a light source on the surface. Evaluable reflections, however, only occur if the alignment of both the lighting and the sensor relative to the surface is exactly the same. If the surfaces under consideration are not flat, this alignment does not fit everywhere and evaluation of the reflection requires considerably more effort.

The Fraunhofer IOSB's RRE principle (retro-reflection ellipsometry) is used to evaluate the reflection of a light source on the surface in retro-reflection. It is not necessary to align the components of the inspection system precisely with the surface under investigation. The real-time image acquisition and evaluation of an RRE inspection system allows the inspection of flat and curved surfaces in a continuous process.

The principle

Ellipsometry as a tool for the examination of surfaces has so far been used rather rarely in industry despite its wide range of applications. One reason for this is the necessary accuracy in matching the positions of light source and detector. The light from the light source is reflected on the test specimen according to the law of reflection and enters the detector. The deviation from the law of reflection may only be 1°. By using a transceiver and retroreflector, the examination of the surface of the object can be carried out under all possible position settings of light source and detector. Thus, even objects with unusual geometry can be examined. The light beam changes its polarisation twice. By measuring the intensity of different polarisation directions, the surface of the object under test can then be reconstructed.