High-efficiency Coherence-Preserving Harmonic Rejection with Crystal Optics
Fan Zhang, Andrew J. Allen, Lyle E. Levine, Gabrielle G. Long, Ivan Kuzmenko, Jan Ilavsky
We report a harmonic rejection scheme based on the combination of Si (111) monochromator and Si (220) harmonic-rejection crystal optics. This approach is of importance to a wide range of X- ray applications in all three major branches of modern X-ray science (scattering, spectroscopy, imaging) based at major facilities, and especially relevant to the capabilities offered by the new diffraction-limited storage rings. We demonstrate both theoretically and experimentally that when used with a synchrotron undulator source over a broad range of X-ray energies of interest (from below 7 keV to above 25 keV), the harmonic-rejection crystals transmit the incident harmonic X- rays on the order of 10-6. Considering the flux ratio of fundamental and harmonic X-rays in the incident beam, this scheme achieves a total flux ratio of harmonic radiation to fundamental radiation on the order of 10-10. We also demonstrate that the spatial coherence of the undulator beam is preserved in the transmitted fundamental radiation while the harmonic radiation is suppressed, making this scheme suitable not only for current third-generation synchrotron sources but also for the new diffraction- limited storage rings where coherence preservation is an even higher priority. Compared to conventional harmonic rejection mirrors, where coherence is poorly preserved and harmonic rejection is less effective, this scheme has the added advantage of lower cost and footprint. With minor modification, the harmonic rejection can be improved by a further 5 orders of magnitude where this could open even more performance capabilities. Our approach has been successfully utilized at the ultra-small angle X-ray scattering instrument at the Advanced Photon Source for scattering, imaging, and coherent X-ray photon correlation spectroscopy experiments.
, Allen, A.
, Levine, L.
, Long, G.
, Kuzmenko, I.
and Ilavsky, J.
High-efficiency Coherence-Preserving Harmonic Rejection with Crystal Optics, Journal of Synchrotron Radiation, [online], https://doi.org/10.1107/S1600577518009645
(Accessed February 3, 2023)