Chania, Griechenland  /  9.10.2018  -  12.10.2018

International Conference on Space Optics ICSO 2018

Die Entwicklung von optischen Schichten für Anwendungen im Bereich der Luft- und Raumfahrt ist aus der Forschungsarbeit des Fraunhofer IST nicht mehr wegzudenken. Auf der diesjährigen International Conference on Space Optics ICSO stellt Dr. Michael Vergöhl, Leiter der Abteilung »Niederdruckplasmaverfahren« am Fraunhofer IST, seine Forschungsergebnisse zur Uniformität und Wellenfrontkontrolle optischer Filter vor und ergänzt damit das wissenschaftliche Programm der 4-tägigen Konferenz im griechischen Chania. Der Wissenschaftler gibt außerdem Einblicke in die Entwicklung eines Bandpassfilters bei 670nm, der auf einer Linse aufgebracht ist. Die durch Magnetron-Sputtern in der EOSS®-Beschichtungsanlage beschichtete Linse soll praktisch keine spektrale Verschiebung der Durchlassbandposition aufweisen.

 

Freitag, 12. Oktober 2018

11:20 - 12:40 Uhr

»Uniformity and wavefront control of optical filters«

Michael Vergöhl, Chris Britze, Stefan Bruns, Tobias Zickenrott, Andreas Pflug, Jennifer Ahrens, Bernd Schäfer, Klaus Mann, Volker Kirschner

The present paper addresses uniformity effects in demanding dielectric optical coatings made by magnetron sputtering. Recently it was observed that in a dielectric beamsplitter coating, surprisingly large, resonant like errors of the reflected wavefront occur at specific wavelengths [Venancio2016]. In the present paper, the origins of these wavefront errors (WFE) induced by coating non-uniformities are investigated in detail. The coating is a broad-band beamsplitter with a high reflectance between 400 and 900 nm and a high transmittance between 920 and 2300nm. It is found that the WFE can significantly be reduced with an optimized design. A new setup to measure the spectrally dependent WFE in the visual wider spectral range based on Hartmann-Shack measurements was built. A method for referencing the measurement data is presented. The WFE maps obtained by spectral Hartmann-Shack measurements are compared with those obtained by spectral photometric measurements. Uniformity and spatial control of the layer thickness is also important for the deposition on curved surfaces. The second part of the paper will address the development of a band pass filter centered at 670nm and with a broad blocking range from 200 to 1100nm on a curved lens surface. Virtually no spectral shift of the passband position overall the lens surface shall occur. A combination of a sub-rotation with a shaping mask was used to deposit the lens by magnetron sputtering with the EOSS® turntable coater. For theoretical analysis of the coating profile, the 3D plasma of the magnetron discharge in the sputter compartment was simulated with a particle in cell Monte Carlo Simulation code [Pflug2013]. To simulate the deposition profile on the (moving) lens and also to design the shaping mask, an improved method was used. Results of coatings and measured single layers and filters will be presented in the paper.