Electronic and optical moire interference with microchannel plates: artifacts and benefits

The spatial resolution of position-sensitive detectors that use stacks of m icrochannel plates (MCP's) with high-resolution anodes can be better than 2 0-mu m FWHM [Proc. SPIE 3114, 283-294 (1997)]. At this level of accuracy, c hannel misalignments of the MCP's in the stack can cause observable moire i nterference patterns. We show that the flat-field detector response can hav e moire beat pattern modulations of as great as similar to 27% with periods from as small as a few channel diameters to as great as the size of a MCP multifiber. These modulations, however, may he essentially eliminated by ro tation of the MCP's or by a mismatch of the channel sizes. We also discuss how the modulation phenomena can be a useful tool for mapping the metric no nlinearities of MCP detector readout systems. Employing the optical moire e ffect, we demonstrate a simple, but effective, technique for evaluation of geometrical deformations simultaneously over a large MCP area. For a typica l MCP, with a 60-channel-wide multifiber, we can obtain accuracies of 1.2 m rad for multifiber rotations and twists and 35/(L/p) mrad for channel-long axis distortions (where L/p is MCP thickness to interchannel distance ratio ). This technique may be used for the development of MCP x-ray optics, whic h impose tight limitations on geometrical distortions, which in turn are no t otherwise easily measurable with high accuracy. (C) 1999 Optical Society of America.