Position offsets in curved-channel microchannel plate detectors

Electronic and optical moi? Interference with microchannel plates: artifacts and benefits

The spatial resolution of position-sensitive detectors that use stacks of microchannel plates (MCP's) with high-resolution anodes can be better than 20-microm FWHM [Proc. SPIE 3114, 283-294 (1997)]. At this level of accuracy, channel misalignments of the MCP's in the stack can cause observable moiré interference patterns. We show that the flat-field detector response can have moiré beat pattern modulations of as great as approximately 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 be essentially eliminated by rotation 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 nonlinearities of MCP detector readout systems. Employing the optical moiré effect, we demonstrate a simple, but effective, technique for evaluation of geometrical deformations simultaneously over a large MCP area. For a typical MCP, with a 60-channel-wide multifiber, we can obtain accuracies of 1.2 mrad 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, which impose tight limitations on geometrical distortions, which in turn are not otherwise easily measurable with high accuracy.

Comparison of the imaging characteristics of curved-channel and straight-channel microchannel plates

We have measured and compared the spatial fidelity of two types of microchannel plates over roughly half of their active area. Measurements of the spatial fidelity of curved-channel microchannel plates confirm earlier reports of large (>25 microm), irregular position offsets between the front and the back of the microchannel plates. Straight-pore microchannel plates used in a chevron configuration, on the other hand, showed almost no such position offsets (<4 microm).