FUSE Gratings

Caption: A prototype FUSE spectrograph grating being removed from a vacuum tank in a clean room at Jobin Yvon in France. The FUSE gratings are approximately a foot square, and contain some 5300 - 5800 lines per millimeter etched onto its surface. (The exact number changes as a function of position across each grating, and they are slightly curved, so we can't strictly call them parallel!) These etchings are what disperse far-UV light into a spectrum for analysis, and provide the high spectral resolution of the spectrograph. Placing these complicated etchings onto the curved surface of the grating was a particularly difficult task carried out by our French colleagues.

It is interesting to note that if the lines on a FUSE grating were all placed end to end, the resulting line would be over 300 miles long!

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Caption: A side view of the top end of FUSE during integration at JHU/APL. This picture shows two of the four FUSE gratings (under red covers) as mounted in the spectrograph. (May. 1998.)

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