FUSE microchannel plate detectors: models and data for resolution at the pore limit

For detectors using microchannel plates (MCPs), the nonuniform response introduced by the finite size of the MCP pores has a significant effect when the size of a resolution element is comparable to the spacing between the pores (approximately 10 - 15 micrometers ). For the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrograph, which will employ a delay line detector, the instrument plate scale, nominal slit width (1 arcsecond), and well-corrected optical design combine to produce slit-limited images 25 micrometers in width with resolution elements 32 micrometers wide, and a nominal resolution of (lambda) /(Delta) (lambda) equals 30,000. At these scales, the MCPs will sparsely sample spectral line images, resulting in significant pixellation effects. We have constructed a computer model of a microchannel plate detector to simulate these effects and evaluate the performance that can be expected from the FUSE detector. These simulations have been compared to actual images obtained with a laboratory version of a delay line detector. Slit patterns imaged onto the detector were chosen to simulate the resolution expected from the FUSE spectrograph in order to provide an estimate of the expected resolving power and test the effects of several detector parameters on resolution. Details of the model are described, and a comparison of the results with laboratory data is made. The implications for FUSE are also discussed.