Explain the theory of formation of spectra by a concave grating and describe the Eagle's mounting.
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Answer:
The theory of the concave grating has been examined in considerable detail by methods of geometrical optics. The results derived by means of geometrical optics were checked by comparing them with those based on physical optics in special cases. The conditions for image formation and aberrations in the image may be expressed by equations somewhat different from those given by Beutler which are shown to be in error. The astigmatism and other aberrations are treated with respect to finite length of slit illumination, finite grating size and deviations of the optical components from the Rowland plane but still lying on the Rowland cylinder. Within certain limitations, it is shown that the aberrations present in an off-plane Eagle mounting may be corrected by a very small rotation of the slit in a plane perpendicular to the optic axis. The optimum width of the grating, instrumental line half-width, and resolving power of the grating are also discussed. Finally, the Beutler treatment of the concave grating is examined in detail and the important errors are pointed out.
Answer:
The idea of the concave grating has been tested in big element through strategies of geometrical optics. The effects derived by way of geometrical optics have been checked through evaluating them with the ones primarily based totally on bodily optics in unique cases. The situations for photograph formation and aberrations withinside the photograph can be expressed through equations quite exceptional from the ones given through Beutler which might be proven to be in error. The astigmatism and different aberrations are handled with appreciate to finite duration of slit illumination, finite grating length and deviations of the optical additives from the Rowland aircraft however nevertheless mendacity at the Rowland cylinder. Within positive limitations, it's miles proven that the aberrations found in an off-aircraft Eagle mounting can be corrected through a totally small rotation of the slit in a aircraft perpendicular to the optic axis. The premier width of the grating, instrumental line half-width, and resolving energy of the grating also are discussed. Finally, the Beutler remedy of the concave grating is tested in element and the vital mistakes are pointed out.
A mounting for a diffraction grating, primarily based totally at the precept of the Rowland circle, wherein the diffracted ray is again alongside almost the equal route because the incident beam.
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