X-RAY FOCUSING USING CYLINDRICAL-CHANNEL CAPILLARY ARRAYS .1. THEORY

A detailed analysis of the focusing and collimation of x rays by circu lar-pore microchannel plates (MCP's), or arrays of cylindrical capilla ries, is presented. The focusing effect derives from external reflecti on of grazing-incidence rays at the interior surfaces of the hollow ch annels of the MCP and is similar to optical focusing by a spherical mi rror. We give the point spread function of an MCP, taking into account surface roughness and misaligned channels. The calculation is based o n multiply reflected rays and skew rays and is valid for a spherically curved MCP of any thickness. For comparison with experimental results the effects of a finite source and a detector aperture are also evalu ated. This theory is compared with experiment.