Examination of the Spectral Efficiency of an Echelle Grating Monochromator

Abstract
The spectral efficiency of an echelle grating monochromator has been examined. The frequently cited advantage that “echelles are blazed at all wavelengths” is observed to be a result of the periodic character of the echelle efficiency as compared with the continually decreasing efficiency from the blaze wavelength for conventional gratings. The periodic character of the echelle efficiency may be also a disadvantage, particularly when regions near the ends of the orders are utilized, since the efficiency may drop significantly below the theoretical decrease of 50%. An awareness of the efficiency character of the echelle grating monochromator should facilitate the choice of wavelength region in which to work