Concave reflecting holographic diffraction grating - is used with fixed entrance and exit slits and is rotated

摘要

A method is used for focussing concave diffraction gratings, operating on the reflection principle, in order to disperse the various radiations from a polychromatic light source. Fixed entrance and exit slits are used and the grating is simply rotated in order to spread out the various radiation in the plane of the exit-slit. The grating is a spherical or aspherical holographic grating. The point sources for recording the grating are positioned so that phase variations created on the grating compensate the phase variations related to the resultant astigmation of the mounting. The midpoint of the entrance and exit slits is positioned in a plane containing the normal to the grating and perpendicular to the direction of its lines.