Fabrication of collimating grids for an x-ray solar telescope using LIGA methods

Abstract

 We are fabricating sub-collimating X-ray grids that are to be used in an orbiting solar X-ray telescope. The telescope optics consist of twelve rotating pairs of high aspect ratio grids. The pitch for the grids ranges from 34 μm to 317 μm. The grid thickness-to-grid-slit ratio must be approximately 50:1, resulting in grid thicknesses of 1 to 10 millimeters. We are implementing a design in which a 34 μm pitch, free-standing PMMA grid is fabricated with 20 μm wide slits through a 800 μm thickness. After exposure and developing, metal is electrodeposited into the slits in the PMMA grid and the PMMA is left in place to hold the individual metal pieces. For optimum imaging performance, the root-mean-square pitch of the two grids of each pair must match to within 1 part in 10000 and simultaneous exposures of stacked sheets of PMMA have insured that this requirement is met.