title: Focusing polycapillary to reduce parasitic scattering for inelastic x-ray measurements at high pressure.
abstract: The double-differential scattering cross-section for the inelastic scattering of x-ray photons from electrons is typically orders of magnitude smaller than that of elastic scattering. With samples 10-100 μm size in a diamond anvil cell at high pressure, the inelastic x-ray scattering signals from samples are obscured by scattering from the cell gasket and diamonds. One major experimental challenge is to measure a clean inelastic signal from the sample in a diamond anvil cell. Among the many strategies for doing this, we have used a focusing polycapillary as a post-sample optic, which allows essentially only scattered photons within its input field of view to be refocused and transmitted to the backscattering energy analyzer of the spectrometer. We describe the modified inelastic x-ray spectrometer and its alignment. With a focused incident beam which matches the sample size and the field of view of polycapillary, at relatively large scattering angles, the polycapillary effectively reduces parasitic scattering from the diamond anvil cell gasket and diamonds. Raw data collected from the helium exciton measured by x-ray inelastic scattering at high pressure using the polycapillary method are compared with those using conventional post-sample slit collimation.
authors.affiliation: HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
authors.forename: P
authors.initials: P
authors.lastname: Chow
authors.affiliation: HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
authors.forename: Y M
authors.initials: YM
authors.lastname: Xiao
authors.affiliation: HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
authors.forename: E
authors.initials: E
authors.lastname: Rod
authors.affiliation: HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
authors.forename: L G
authors.initials: LG
authors.lastname: Bai
authors.affiliation: HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
authors.forename: G Y
authors.initials: GY
authors.lastname: Shen
authors.affiliation: HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sinogeikin
authors.affiliation: Center for X-Ray Optics, University at Albany, State University of New York, 1400 Washington Avenue, Albany, New York 12222, USA and X-Ray Optical Systems, Inc., 90 Fuller Road, Albany, New York 12205, USA.
authors.forename: N
authors.initials: N
authors.lastname: Gao
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Ding
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.
authors.forename: H-K
authors.initials: HK
authors.lastname: Mao