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13 October 1986 A Grazing Incidence Extreme Ultraviolet Spectrometer For Use With A Diverging Beam
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Although previous work has emphasized the usefulness of gratings placed at grazing incidence in converging beams1'2 for extreme ultraviolet astronomy specific applications may well require a design that can be placed behind a slit at the prime focus of a telescope. Hence we have designed a grazing incidence spectrometer that accepts a diverging beam and performs moderate resolution spectroscopy. To enable a comparison with other recently pro-posed designs we limit our analysis here to an extreme ultraviolet spectrometer covering the 100 to 350 A bandpass. We assume that the diverging beam from the telescope has a focal ratio of 10. We find that an efficient spectrograph can be designed which has as its first optic an off-axis ellipsoid used at grazing incidence to refocus the diverging beam and increase the focal ratio. Any of a variety of gratings could be placed at grazing incidence in this slowly converging beam; we study in detail the performance of a plane, straight groove variable line space grating. Grating aberrations are evaluated analytically and verified by geometrical ray-tracing. Off-axis aberrations are determined by geometrical raytracing. The resolution of the system is a function of the telescope image quality. An optimum design is found by varying six parameters and maximizing the average resolution over the bandpass, assuming a telescope blur of 75 microns (corresponding to 1.5" at the focus of a telescope with focal length 10 meters). The resolution of this optimized design varies from 300 to 800 across the bandpass. The spectrometer can be located far from the optical axis of the telescope and fed by a small grazing incidence pick-off mirror. This represents a spectrometer which can be removed from the light path easily and thus would be a particularly compatible adjunct to other spectrometers that also utilize the f/10 diverging beam.
© (1986) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mark Hurwitz and Stuart Bowyer "A Grazing Incidence Extreme Ultraviolet Spectrometer For Use With A Diverging Beam", Proc. SPIE 0627, Instrumentation in Astronomy VI, (13 October 1986);

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