Istituto Nazionale Di Fisica Nucleare

Augusto Marcelli

Mikhail I Mazuritsky

Alexandre V Soldatov

A diffractor for electromagnetic radiation with a spherical stepped geometry constructed under the constant step width conditions (here defined as pseudo-spherical geometry). The diffractor consists of a plurality of spherically curved dispersive elements (oriented monocrystals, crystal surfaces or gratings) that are located on a focal circle. The location on the focal circle of each element is made to guarantee the same Bragg angle for the incident radiation. Thus a diffractor is an array of diffracting elements (&ldquo;steps&rdquo;) each one contributing to the total solid angle of the diffractor, that increase the spectral output of the device without decreasing the resolution. Because the steps are spherically curved, they are curved also in the direction perpendicular to the focal circle in order to satisfy Bragg's law for diffraction over a maximum area of the diffractor. The geometry proposed for the diffractor, is defined as pseudo-spherical because the footprint of the Bragg diffraction area on each step is that of a spherical crystal, therefore superior to any alternative cylindrical, also stepped, geometries. Scheme and parameters of different devices based on the analysis of x-rays secondary are described. Indeed, many standard devices may be rebuilt using this geometry: high resolution secondary monochromators for x-ray absorption spectroscopy, extremely high resolution monochromators for hard x-ray and neutron radiation, monochromators for x-ray microanalyzer and x-ray photoelectron spectrometers for chemical analysis (ESCA).

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Frascati, Italy

Augusto Marcelli