Analysis of powder X-ray diffraction resolution using collimating and focusing polycapillary optics

Focusing X-ray optics can be used to increase the intensity onto small samples, greatly reducing data collection time. Typically, the beam convergence is restricted to avoid loss of resolution, since the focused beams broaden the resulting powder diffraction rings. However, with smooth Gaussian peaks, the resolution defined by the uncertainty in peak location can be much less than the peak width. Polycapillary X-ray optics were used to collimate and focus X-rays onto standard inorganic powder diffraction samples. Comparisons were made of system resolution and diffracted beam intensity with and without focusing and collimating optics using a standard small spot rotating anode system in point source geometry. The area detector and optics also allowed for the use of a low power 60 W source, without increasing either the collection time or the peak center error compared to the rotating anode no optic case. Resolution and intensity were in good agreement with those obtained from a simple geometrical model developed for the optics, which allows for system design and optimization for the desired sample characteristics. Foils and powders were used to model thin film samples while allowing both reflection and transmission measurements to more effectively verify theoretical modeling of beam parameters.