SCATTERED-LIGHT PROPERTIES OF DIFFRACTION GRATINGS

One of the many calibrations performed for a scientific-quality spectr ometer is the characterization of its scattered-light properties. The scattered light can arise from any optical surface, and light leaks or scattering from baffles can also contribute to the instrumental stray -light level. For a diffraction-grating spectrometer the primary contr ibution to instrumental scattered light has been found to be the scatt ered light from the grating. The results from measuring the scattered- light properties of 10 diffraction gratings are discussed along with t he application of these results in analyzing the total scattered light measured for three spectrometers. It has been found from these measur ements that there are two components of the grating scattered light: a Lorentzian-type component and a constant background component. The Lo rentzian component is predicted from the diffraction theory for a grat ing, and the constant background component is consistent with Rayleigh scattering from the microscopic surface imperfections. It was also di scovered that multiple replicas of gratings from the same master grati ng exhibit significantly more scattered light than the preceding repli ca by factors of 1.1-2.