To reduce the uncorrected higher-order aberrations for holographic
gratings requiring an extreme dispersion, we have modified the Rowland
mounting by moving the recording laser sources away from the
grating. Then, with a multimode deformable plane mirror to record
the grating, the correction of all the aberrations up to the fourth
order inclusive is found sufficient to obtain a high-quality
image. Applied to the FUSE-LYMAN grating, with a groove density of
as much as 5740 grooves/mm, for which a resolution of 30,000 was
required, this new recording device produces a resolution from 139,000
to 222,000 over the spectral range.
© 2000 Optical Society of America
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