New monochromators of concave grating suitable for space telescopes.

Three types of new monochromators based on the new mounting of concave grating by Singh-Majumdar (SM) are described. These monochromators are very compact and simple in operation, fulfilling the requirements of a monochromator in a space telescope in the VUV region. It is found theoretically (by geometric optics theory of concave diffraction grating given by Beutler and modified by Namioka, and by a ray tracing procedure by drawing spot diagrams at different wavelengths) as well as experimentally in the laboratory by setting up the monochromator and taking sample spectra photographically that the spectral images have very little aberration as compared to other monochromators in the VUV region. The improvement obtained is three times.