Practically all thin film systems for normal incidence can be realized using only two-layer materials. But for oblique incidence, polarization effects occur, designs may become complex, and polarization control is difficult or impossible to achieve. Here multi-index or gradient designs offer additional degrees of freedom, and can simplify or even enable challenging designs. Such gradient thin film stacks can be designed ab initio without any start or index profile approximations using a new design software developed by Carl Zeiss. With this software, a rugate omnidirectional AR coating was calculated and transferred to three different multi-index systems. All three examples were realized using ion beam sputter technology, and characterized at Laser Zentrum Hannover. Here we present comparative measurements of the optical performance together with femtosecond laser-induced damage threshold measurements.
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