A method capable of giving quantitative information about the resolving power of large high-quality diffraction gratings has been developed. This method is based on the ability of the grating to resolve the perpendicular components of a normal Zeeman triplet when the central parallel component is removed. Since the splitting of these components is a known function of the field strength, one has in effect two lines whose separation can be varied at will, thus providing as stringent a test for the grating as is necessary. Suitable corrections are made for the effect of Doppler breadth in the source and for the finite width of the slit.
An excellent plane grating has been obtained from Bausch & Lomb Optical Company. Its resolving power has been measured by this method under various conditions and is shown to be a constant fraction of the theoretical value.
The effects of error of run on resolution and focus have been reviewed and investigated experimentally. Nonplaneness of the grating blank has been measured in order that the contribution of this defect to the focal curve can be calculated and separated from the shift of focus caused by linear error of run.
© 1955 Optical Society of AmericaFull Article | PDF Article
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