The Fraunhofer IST's EOSS® system platform saw further development in 2015 as well. Industrial users make high demands of the system's stability in production. Unvarying implementation of specifications requires a stable distribution of layer thickness. With the EOSS® it could be demonstrated that the concept of rotating cathodes and optimized sputtering targets is well suited for delivering outstanding homogeneity in optical filter coatings even over very long periods of weeks and months.

EOSS® coating concept

In the production of optical coatings the Fraunhofer IST relies on using magnetron sputtering technology. With the EOSS® platform an approach has been selected in which a batch often substrates each with a diameter of 200 mm is arranged on a turntable which rotates continuously at a fast speed. Using cylindrical magnetron sources rather than planar magnetrons yields decisive advantages, since the layer thickness distribution is extremely stable in the long term. The advantage is obvious: readjustments, batch planning or other measures are no longer necessary. In the case of the sputtering cathodes, sub-stoichiometric oxides among other things are used as targets. Previous research showed that this leads to improved values for the layer thickness distribution and that conditioning can be simplified significantly. Current measurements at the Fraunhofer IST show that absorption is even improved in the case of Ta2O5 as a high-index material.

Precision optical filters for laser projection

The Picture shows an example of an optical filter which was produced with the new EOSS® technology. This is a so-called “notch“ filter, in which light transmission in the “green“ spectral region of 532 ±10 nm is reduced by 6 orders of magnitude. Transmission here is thus less than 10– 4 %. In the remaining spectral region between 200 and 1100 nm the filter has a high transmission of more than 95 %. This kind of filter serves as a blocking filter. The high blocking effect is necessary due to the fact that fluorescent intensities are very low and the detectors can measure extremely low light intensities, which means that a high level of scattered-light suppression must be assured. In some cases notch filters with over OD10 are required today and this calls for almost flawless coatings. EOSS® technology is able to satisfy even extreme requirements of this kind.

The Fraunhofer Group for Light & Surfaces

Further information about the Hannover Messe 2019 and on the exhibits exhibited by the Fraunhofer Light & Surfaces Group can be received on a regular basis on our homepage under “Press & Events“.

The Fraunhofer Light & Surfaces Alliance brings together the expertise of six Fraunhofer Institutes. The institutes combine coordinated competencies in the fields of laser manufacturing processes, laser beam sources, measurement technology, medicine and life sciences, optical systems and optical manufacturing, EUV technology, process and system simulation, materials technology, micro- and nanotechnology, thin-film as well as plasma and electron beam technology.