Beam Collimation using Polycapillary X-ray optics for Large Area Diffraction Applications

Applications S.D. Padiyar, Hui Wang, M.V. Gubarev,* W.M. Gibson, and C.A. MacDonald Center for X-ray Optics, University at Albany, State University Of New York at Albany, 1400 Washington Avenue, Albany, New York 12222 *Currently at Marshall Space Flight Center, Huntsville, Alabama 35824. Abstract Polycapillary optics, arrays of thin-walled, hollow borosilicate glass channels, can be employed to redirect, collimate and focus x-ray photons. Polycapillary collimating optics collect x-rays over a wide solid angle (as large as lo-15 degrees cone angle) and a large energy bandwidth and provide a quasi-parallel beam with a small divergence (a few milliradians). Parallel beam geometry and uniform local divergence give symmetric uniform peak shapes. This combined with the diffracted beam intensity gain allows accurate analysis of thin complex multilayer diffraction peaks. Experimental results are compared to Monte-Carlo geometrical optics simulations to study performance characterization of polycapillary collimating optics. In-situ thin film growth monitoring times, utilizing x-ray diffraction, could be reduced significantly by employing capillary optics. Suppression of higher energy Bremsstrahlung and background rejection accompanied by the benefit of increased tube potential enhances the signal to noise ratio for thin film analysis. Introduction Polycapillary x-ray optics are composed of glass fibers, each made up of hundreds of hollow thin walled channels. Grazing incidence x-ray photons are guided along these microchannels by total reflection,’ as exploited in grazing incidence mirrors commonly used on synchrotron beam lines. The reflectivity of these channels remains high as long as the glancing angles are kept below the critical angle for total external reflection, 0,.2 The channels must be gently curved and kept small enough that the maximum angle of incidence is kept smaller than the critical angle &, as illustrated in figure 1. The reflectivity is higher at smaller angles, even at angles below the critical