High-dispersion spherical holographic gratings in a modified Rowland mounting

For holographic gratings requiring an extreme dispersion, I consider a modi fied Rowland mounting, in which the recording laser sources are moved away from the grating, to reduce the uncorrected higher-order aberrations. In ad dition, I choose the geometric parameters such that first-type coma is corr ected. Then a plane multimode deformable mirror (MDM) or two auxiliary sphe rical holographic gratings (R3 device) are used to aberrate the grating's r ecording sources; correction up to the fourth order is sufficient to obtain high image quality. Applied to the FUSE-Lyman (FUSE is Far Ultraviolet Spe ctroscopic Explorer) grating, with a groove density as high as 5767 grooves /mm, these recording devices produce a resolution (chromatic resolving powe r) as great as 611,000 with the MDM and 3,030,000 with the R3 device. These results far exceed the specified performance of 30,000. Since diffraction limits the resolution to 482,000, the images are diffraction limited with b oth devices. (C) 2001 Optical Society of America.