Theory of Monochromators Using Concave Holographic Diffraction Grating and Collimated Illumination

Abstract

In this paper we have discussed the basic principle and aberration properties of monochromators in which a concave holographically produced diffraction grating is used as the dispersing and focusing optical element and a concave mirror as the collimating device. The grating is constructed by recording the interference fringes on a concave spherical surface, formed by two beams of coherent radiation. One beam is parallel to the axis of the spherical surface whereas the other beam diverges from an axial point of the spherical surface. While in actual use, the grating is kept in its original recording position and illuminated with a collimated beam of polychromatic light. For scanning the spectrum the grating is moved along the axis on both sides of its original recording position. Based on the above principle some possible instrument geometries having moderate dispersion and resolution properties have been discussed.