Instrumental aspects of x-ray microbeams in the range above 1 keV

X-ray microscopy has the capability of looking into normally opaque samples with high resolution. X rays are sensitive to elemental, structural, and c hemical content and thus can provide microscopic maps of the composition an d structure of a sample. X-ray microscopy has seen great growth in the last two decades in the number and types of operating instruments as well as th eir capabilities. This growth is due to two developments. The first is the development of high-brightness second- and third-generation synchrotron lig ht sources that can be used with small-aperture optics. The second is a rev olution in x-ray optics. In addition to the extension of commonly used visi ble optics, such as Fresnel zone plates and multilayer mirrors, into the x- ray regime, there has also been a dramatic improvement in grazing-incidence optics fabrication. In the range up to a few keV, Fresnel zone plates offe r the highest resolution, which is below 100 nm in several instruments. Rec ent developments in fabrication may lead to their application at higher ene rgies; for now, however, sub-mu m diffractive microfocusing at higher energ ies is usually achieved by Bragg-Fresnel optics, Fresnel optics operated in reflection using either crystal planes or multilayer coatings. Although th ese offer very high resolution, they have small collection apertures and li mited wavelength range of operation. The Kirkpatrick-Baez mirror combinatio n remains the most popular and versatile microprobe in the x-ray regime. Th ese systems can operate over a very broad energy range and several faciliti es are now operating with micron-scale resolution. We will discuss these an d some newer types of x-ray focusing schemes. (C) 1999 American Institute o f Physics. [S0034-6748(99)01304-0].