As for x-ray Fresnel lenses, the paper John Denker pointed out is a good
paper, and I'm glad he pointed it out and that I read it. But it should
also be stated that they were barely working with x-rays; they indeed
referred to them as "soft x-rays." The line between x-rays and UV is
fuzzy, but some put it at roughly 10nm wavelength (124 eV) or at roughly
100 eV (12 nm).
In the paper they achieved a spatial resolution of about 5 nm using
x-rays of about 3 nm. While "soft x-rays" is legitimate wording for
that, it's pretty close to "hard UV." The real challenge is to develop
lenses for higher-energy x-rays with energies of hundreds, thousands, or
tens-of-thousands eV energies.
It's difficult to imagine Fresnel technology for x-rays that are more
clearly what one thinks of as traditional x-rays. In order to get the
fine zones, the Fresnel-plate fabrication (of the paper JD referenced)
used thin-film fabrication techniques. In order for the "opaque
regions" to block the more energetic x-rays, a zone plate would have to
be much thicker than "thin film" and that would eliminate the thin-film
fabrication technique that is capable if producing the fine structure
needed.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu