Development of an ion beam sputtering process for 2 meter optics in astronomy - IBS2000

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Resolution and reach of the telescopes in astronomical research depend directly on the optical design and specifically on the size of the optics. All currently planned telescopes and those under construction utilize the approach of very large primary mirrors to collect more than an order of magnitude more light and supply higher resolution. Among these are the European Extremely Large Telescope, the Thirty Meter Telescope or the Giant Magellan Telescope, to name a few.With large primary optics, of course also the instrument and detector optics follow a design of increased optical apertures compared to state-of-the-art concepts. Other than the metallic broadband reflecting mirrors of the primary optic, these instruments are in need of filter coatings that can only be realized with dielectric multi-layer coatings. For these components, selecting a specific spectral range or combining or separation of the guide star laser beam are necessary characteristics that call for complex multi-layer dielectric mirrors. For example the MAORI instrument of the E-ELT will need dichroic and filter optics in the range between 1m and 2m in diameter. These challenging optical features and the requirements in environmental stability will need a filter produced by a precise sputtering technique, others do not provide dense enough films and a stable enough production process in order to meet the spectral requirements. In specific, ion beam sputtering (IBS) is the process of choice for these kind of coatings. However, coating processes available on the commercial market only have capabilities of coating optical apertures of 500mm – 600mm in diameter, some have shown 1m on a trade fair show, but do not offer these coatings anymore. Clearly, there is no coating process available at the moment to supply the filter coatings for the astronomical instruments. Part of the reason for this is that up-scaling the coating process area is nothing that can be achieved without assisting with theoretical considerations in the process design. This work requires a simulation tool that can derive the synthesis of a dielectric film in vacuum coming from a vacuum sputter environment. In addition, the sputtering ion source needs to be designed in a way that a movement within the vacuum chamber is possible. Over the past years this expertise has been built up at Laser Zentrum Hannover and combined with a detailed experience in gridded ion sources and vacuum machine design, it is possible to develop a process that can deposit dielectric multi-layer coatings on up to 2m free apertures. By means of this large aperture IBS coating system, these required filter optics for the instruments are made possible and the full potential of these upcoming telescope systems will be accessible.