X-ray focusing using square channel-capillary arrays

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Abstract
A class of imaging, condensing, and collimating devices for x rays is investigated which is based on the use of an array of small channels of square cross section. The focusing and collimating effect arises from external reflection of near‐grazing‐incidence rays at the interior channel surfaces. Rays are redirected by being singly reflected from two orthogonal channel surfaces and are imaged from a source point to a square region with a side length MT+1 times that of the channel side length, where MT is the transverse magnification. The image and source locations are related by a thin‐lens formula. The point spread function and the efficiency of these focusing devices are calculated. Two energy regimes with different channel reflectivity characteristics are examined in detail: the hard x‐ray regime (E>8 keV) and the soft x‐ray regime (E<200 eV). For these cases the efficiency of focusing x rays depends only on the channel aspect ratio and reflectivity parameters. A discussion is made of channel plates of other configurations, such as arrays of rectangular channels. The results are supported by Monte Carlo simulations.