TOROIDAL CONDENSER OPTICS FOR DARK-FIELD X-RAY MICROSCOPY

The optical system for a dark-field X-ray microscope is described. In particular, the optics for condensing the X-rays onto the specimen are discussed in detail. The microscope is designed for use with two type s of source, line and continuum; for the former a toroidal mirror will be used while for the latter the mirror will be replaced by a toroida l grating to perform simultaneous focusing and dispersion. The design criteria for these optics are discussed and a procedure for minimising the aberrations at the specimen plane is described; this allows a goo d spectral resolution and minimises loss of flux due to non-dispersive aberration of the grating.