Etude du spectre solaire à l'aide d'un réseau utilisé en incidence rasante.

A lensless grazing incidence reflective focal grating system is described, and the observation of solar spectra in the visible range attaining resolutions of 0.2 to 0.1 A is reported. Using a grating of 30 mm length and 1200 lines/mm, and a telephoto focal length of 200 mm and aperture of F/8, photography of continuous, essentially metallic absorption spectra is achieved. The effective resolution is conditioned by such factors as the theoretical grating resolution, the enlargement due to solar diameter, and the effect of the photographic grain, the telephoto optics, and the Doppler-Fizeau effect. To achieve a similar resolution using a slit light source focused by a lens and a grating of 2500 lines/mm would require a slit width of 0.02 mm, one that is not easy to realize.