Progress toward high-performance reflective and anti-reflection coatings for astronomical optics

There is a continued need for efficient reflective and anti-reflection (AR) coatings for increasingly large optics in astronomy. The requirements for these coatings differ in several respects from those developed for commercial use. In general, they require a broad spectral coverage, high-efficiency, long life under semi-exposed conditions, and the ability to be removed without damage to expensive substrates. UCO/Lick Observatory has undertaken an effort to develop improved coatings for astronomical optics. In this paper, we report on progress toward (a) robust protected silver coatings for telescopes; (b) enhanced silver and aluminum coatings for instruments; and (c) hardened sol-gel AR coatings. Examples of some of our new coatings are in use at Lick and Keck Observatories. The problems involved in successful coatings are multifaceted and we summarize our major findings to date. This includes our requirements, test procedures, and performance and durability results for the three types of coatings mentioned.

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