Abstract: Holographic optical elements (HOEs) become more and more important in modern optics. The most important application of HOEs is a holographic lens working as an imaging element. It is often used in monochromatic light because in polichromatic light the image location strongly depends on wavelength, which is usually a great disadvantage. However, in some cases this drawback can be changed into an advantage when a spectral device is regarded. This single diffractive lens can be applied as a basic element of monochromator or spectroscope. In a spectroscope, an input slit is illuminated by polichromatic light of which the spectral content is to be investigated. Each wavelength is focused into a different point and can be observed at the same time. For spectroscopy of good quality all light spots should be small and spatially separated. There are some difficulties in obtaining such spots sensibly separated along direction different from an optical axis. This difficulty disappears when we regard a monochromator. In a monochromator an input slit is illuminated by the light of continuous spectrum. Each wavelength is focused in a different point along optical axis. By moving an output slit one can choose an image of proper wavelength. For reasons stated above our investigations are limited to the monochromator. To establish optimum geometry parameters of this device it is necessary to analyze the sphero-chromatic aberration of a single holo-lens.!6
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