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Uniformity and wavefront control of optical filters

: Vergöhl, M.; Britze, C.; Bruns, S.; Pflug, A.; Zimara, J.; Schäfer, B.; Mann, K.; Kirschner, V.

Fulltext ()

Sodnik, Z. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
International Conference on Space Optics, ICSO 2018 : Chania, Greece, 9-12 October 2018
Bellingham, WA: SPIE, 2019 (Proceedings of SPIE 11180)
Paper 1118046, 11 pp.
International Conference on Space Optics (ICSO) <12, 2018, Chania>
Conference Paper, Electronic Publication
Fraunhofer IST ()
broadband beam splitter; magnetron sputtering; spectral wavefront error; curved substrate surface; lens coating; band pass filter

The present paper addresses uniformity effects in demanding dielectric optical coatings. The origins of spectral resonant wavefront errors (WFE) induced by non-uniformities in complex dielectric filters 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. The WFE can significantly be reduced with an optimized design. A new setup based on Hartmann-Shack sensors measures the spectrally dependent WFE in the visual spectral range. The paper presents a method for referencing the measured data. The experimental WFE maps obtained by spectral Hartmann-Shack measurements agree well with the expected spectra taken from spectral photometric measurements and the coating design. The paper also addresses coatings on curved surfaces. A band pass filter centered at 670 nm on the convex side of a lens was developed. Using a combination of a sub-rotation and special uniformity masks, a very low spectral shift of the passband position overall the lens surface could be demonstrated. The deposition concept and mask design, respectively, are developed via simulation studies based on a simulation approach shown in [10]. Extension of the model framework by plasma simulation and a concept for computing deposition profiles on moving 3D substrates was required for solving the problem.