5 October 2005 Optical monitoring of rugate filters
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Rugate filters have a high potential for solving specific design problems in many applications of modern optics and lighting technology. However, the exact manufacture of these gradual layer systems is still a challenge which could not be solved completely until today. One of the prominent approaches for the production of rugate filters is based on independent quartz crystal devices measuring the rate of the different coating materials. As an alternative, optical broadband monitoring has been already qualified for controlling the deposition of complicated non quarterwave stacks. In the present study, promising results of this deposition control concept as a direct monitoring of rugate filters will be presented. In a first attempt, the continuous change of refractive indices in the graded layers was transformed to a set of discrete homogeneous sub-layers with thicknesses values of around 5 nm. These discrete layers are realized by defined mixtures of two materials. A data base for the dispersion behavior was created for the different mixing ratios and is employed for the production of such quasi-rugate filters. The optical monitor is operated in the routine mode determining the switching points of the layers. Selected examples will be presented for quasi rugate coatings produced by ion beam sputtering from a movable zone target. Different designs will be discussed considering production problems as well as achievable optical properties.
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Marc Lappschies, Marc Lappschies, Björn Görtz, Björn Görtz, Detlev Ristau, Detlev Ristau, "Optical monitoring of rugate filters", Proc. SPIE 5963, Advances in Optical Thin Films II, 59631Z (5 October 2005); doi: 10.1117/12.625122; https://doi.org/10.1117/12.625122

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