Diffraction of Soft X-Rays by Two Successive Concave Gratings (Diffraction de Rayons X Mous Produit per deux Reseaux Concaves Successifs),

The spectra of soft X-rays having wavelengths greater than about 20 A have been studied by means of optical gratings with grazing incidence. Concave gratings are generally used for this. It seems possible to increase the resolving power of the spectrograph by using two gratings in series. Indeed, the use of two plane gratings increases the dispersion without increasing the diffraction efficiency concave gratings offer better efficiency, but concavity introduces aberrations which modify the distribution of light in the final image. In order to make an attempt at predicting the effect of adding a second grating, the authors have undertaken a calculation of this distributions using a point source whose rays follow paths close to the plane of the Rowland circle. Author