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Introduction Periodic Multilayers Normal-Incidence Multilayer Optics Depth-Graded Multilayers Grazing-Incidence Multilayer Optics Aperiodic and Laterally-Graded
Multilayers Facilities
The short-wavelength/high-energy region of the electromagnetic spectrum
spanning the extreme ultraviolet (EUV) to the hard X-ray presents a particular
challenge to the development of efficient reflective optical elements such as
mirrors and gratings: at normal incidence, the reflectance of even the best
materials begins to plummet in the EUV, and continues to fall rapidly with
increasing photon energy (like E4, in fact), as illustrated, for
example, in the next figure. Consequently, conventional front-surface mirrors
and single-layer reflective coatings are far too inefficient to be useful for
the construction of optical instruments such as telescopes and spectrometers
that are meant to operate at normal incidence with high sensitivity at these
short wavelengths.
Figure 1. Reflectance of aluminum,
silver, and gold, as a function of photon energy at normal incidence. These
materials (and others) can be used to produce conventional front-surface
mirrors that have very high reflectance in the UV, Visible, and IR bands. But
such mirrors are far too inefficient for the construction of high-performance
optical instruments operating near normal incidence in the EUV and X-ray bands.
Multilayer
Coatings, on the other hand, make use of the principle
of optical interference to achieve high reflectance at normal incidence in the
EUV and soft X-ray bands, and in the hard X-ray band at grazing incidence angles
that are several times larger than those possible using front-surface mirrors.
Their high reflection efficiency has enabled remarkable advancements in a
variety of scientific and technological disciplines over the past three
decades, particularly solar physics and astronomy, but also microlithography,
ultrafast science, plasma diagnostics, synchrotron optics, and many other areas
as well.
Introduction Periodic Multilayers Normal-Incidence Multilayer Optics Depth-Graded Multilayers Grazing-Incidence Multilayer Optics Aperiodic and Laterally-Graded
Multilayers Facilities