Investigations of whisper gallery mirrors for extreme ultraviolet and soft x rays

Abstract

We have examined optical constants and predicted reflectivities of candidate surface coatings for whisper gallery mirrors in the extreme ultraviolet (<100-500 Å). Previous work by Vinogradov and co-workers has identified the spectral regime near 100-150 Å to be particularly promising owing to the high whisper gallery mirror reflectivities of the noble metals near their Cooper minima in this regime. We have confirmed this basic result using new optical data, and we have sought surface materials that would extend the range over which the whisper gallery mirrors may be used: 100-500 Å. We have found that substantial whisper gallery mirror reflectivities (near or greater than 50%) are predicted for a variety of elements and that TE peak reflection is larger than TM peak reflection by approximately 10%. However, most of the elements that reflect well have surfaces that are vulnerable to oxygen contamination, which seriously degrades mirror performance. A cryogenic mirror design using a dynamic-solid rare gas surface that has the potential to defeat such surface contaminations will be described, it has peak reflectivity >50% centered near 280 Å.