Multiple Diffraction in Grating Spectroscopy

Double mirrors are used in the focused spectrum of diffraction gratings to invert the spectrum and return the radiation to the grating a number of times. After three or four diffractions from low orders, resolution is observed which is equivalent to that available in the highest orders. An additional double-mirror system is described which separates the spectra, obtained after several diffractions, from other spectra. The problem of multiple diffraction with long-curved slits is discussed, and a modification of the Ebert monochromator is suggested for high-resolution multiple-diffraction spectrometry.