On the theory of the johann focusing spectrometer

The focusing of a spherical X-ray beam according to the Johann scheme is considered based on the dynamic theory of Bragg’s diffraction in a thick crystal. With an allowance for the aberration of a diffracted beam, the beam intensity in the focal region can be described by one of the two analytical expressions, depending on the model selected for the crystal surface bending. The spectral characteristics of the Johann focusing spectrometer are considered in comparison to the existing theory of such spectrometers.