  A further development of a focusing monochromator concept for X-ray energy
resolution of 0.1 meV and below is presented. Theoretical analysis of several
optical layouts based on this concept was supported by numerical simulations
performed in the "Synchrotron Radiation Workshop" software package using the
physical-optics approach and careful modeling of partially-coherent synchrotron
(undulator) radiation. Along with the energy resolution, the spectral shape of
the energy resolution function was investigated. It was shown that under
certain conditions the decay of the resolution function tails can be faster
than that of the Gaussian function.
