26.1 SPECIFIC REQUIREMENTS FOR SYNCHROTRON X-RAY OPTICS

X-ray mirrors have been discussed in detail by Harvey in Chap. 11, Vol. II, of the Handbook of Optics .1 In particular, the basic scattering processes of X rays by surfaces, the effects of surface figure and finish on mirror performance, and the influence of aberrations on the efficiency of various focusing schemes have been described. The applications mentioned were mainly in the field of astrophysics and often in the soft X-ray range. The present section will therefore be limited to facts that are specific to synchrotron radiation applications in the medium and hard X-ray range (i.e., for energies E>1 keV). Recent more general reviews of synchrotron X-ray beam optics have been given by Hart,2 Freund,3 and Hart and Berman.4 More detailed papers on the subject can be found in Vol. 34 of Optical Engineering5 and in recent Proceedings of SPIE Conferences , for example, Vol. 3773.6

Specular reflection of X rays is based on the refractive index whose real part of the decrement, ?, is of the order of 10 ⁵ for X rays, so that the so-called critical angle ? _c=(2 ?) ^1/2 below which total reflection is observed, is very small, of the order of 3 mrad for 20 keV radiation and a heavy metal such as platinum or palladium. The evanescent wave penetrates only a few nm and nearly 100...