X-RAY FOCUSING USING SQUARE CHANNEL-CAPILLARY ARRAYS

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 M(T) + 1 times that of the channel side length, where M(T) 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.