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10 December 2001 Compact optic for 50-nm UV imaging with a diffraction-limited 1-deg angular field
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A four-mirror optic has been derived from a previous three- mirror system, with characteristics that have significant advantages for imaging in the EUV. The compact format enables the total length to be less than the entrance pupil diameter; the focal surface is flat and with rear access; the aperture stop is located coplanar with the secondary, thus ensuring that bignetting is zero and that the pupil is identical at all field angles. Stray light baffling is 100% when the optic is fully enclosed. The aberration correction is good enough for diffraction- limited imaging over most of a 1 degree(s) field angle at wavelengths down to 50nm for a typical 1m entrance pupil diameter. The speed of the 1m pupil diameter example system is f/2.4, but trade-off can be made with other characteristics to achieve faster or slower systems. An f/1.2 system has been designed as an exercise. For all derived systems, scaling is possible to much larger pupil diameters by sacrificing field angle. Realization of the most complex design would require significantly advanced optical fabrication technology. All four surfaces are aspheric, the convex secondary being the only pure hyperboloid. The primary and tertiary can be fabricated on a single substrate. The quaternary mirror is in the form of a zone plate. The performance data for this design show that 90% enclosed energy does not exceed 1 micrometers diameter at all field angles up to 0.4 degree(s) off-axis. Simplified designs are possible for imager devices with larger pixels. For a given pupil diameter, [mass x volume to orbit]-related costs would be unusually favorable.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David A. Beach "Compact optic for 50-nm UV imaging with a diffraction-limited 1-deg angular field", Proc. SPIE 4498, UV/EUV and Visible Space Instrumentation for Astronomy and Solar Physics, (10 December 2001);


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