| 摘要 |
A concave grating having grooves formed in a concave blank surface in which the grooves are so formed as to have a non-uniform, spacing in accordance with the following relationship: <IMAGE> wherein b1, b2 and b3 represent constants; sigma o represents groove spacings at the center of the gratings when the grooves are projected onto a plane which is in contact with a concave surface at the center of the gratings; sigma represents groove spacings at positions w at right angles with the lines from the center of the gratings to the grooves; and R represents a radius of curvature of the concave surface.
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