Aberration-corrected aspheric gratings for far-ultraviolet spectrographs: holographic approach.

Two approaches to reducing the optical aberrations of concave diffraction gratings have been studied: holographically controlling the groove curvature and spacing, and shaping the optical substrate while keeping the grooves straight and equally spaced. We develop the theory of ellipsoidal holographic diffraction gratings and apply this theory to Rowland circle spectrographs. We show that ellipsoidal holographic gratings used in second order can yield high spectral resolutions across the spectral band. These gratings may be suitable for use in far-ultraviolet Rowland spectrographs with small bandpasses.