Theory and design of unusual concave gratings

Thesis (Ph.D.)--University of Rochester. College of Engineering and Applied Science. Institute of Optics, 1970.Technological advances in rocket techniques have made possible the study of far ultraviolet spectra of stellar sources with high resolution spectrographs. It is found that spectrographs of this type require special techniques for aberration control. These techniques include deforming the grating surface, using an off-plane mount, and altering the rulings. Using an optical path difference approach as a basis for an aberration theory of the concave reflection grating, the first few chapters of this thesis presents the derivation of those expressions required for predicting the necessary grating modifications to control astigmatism, coma, and off-plane image rotation. The theoretical development sets no requirements on the location of the object, the shape of the grating surface, or even on the shape and spacing of the rulings. Expressions that accurately predict the ray deviations, at any wavelength, of an arbitrary ray are found. Special ray trace equations are developed for use in verifying the theoretical predictions. A computer design program, based on the theoretical results, is presented. This program has been used to obtain significant improvements in the performance of three Wadsworth type, far-ultraviolet high resolution rocket borne spectrographs. While the methods proposed for aberration control in this case are unconventional the results they produce merit serious consideration in any attempt to optimize the performance of a spectrograph. The present art of grating manufacture allows the production of gratings with unusual surface figures. Consequently, some of the theoretical results are immediately applicable. With regard to gratings with unusual ruling patterns, the theory presented here advances the state of the art of grating design beyond present capabilities of grating manufacture. In view of this it is hoped that added impetus for the development of methods for producing such gratings has been provided since it is shown that unusual ruling patterns can be used effectively to control aberrations