Soft Matter Interfaces beamline at NSLS-II: geometrical ray-tracing vs. wavefront propagation simulations
2014
We report on the implications of the design of a Soft Matter Interfaces beamline, a long energy range canted in-vacuum
undulator (IVU) beamline at National Synchrotron Light Source II, based on comparison of geometrical ray-tracing and
partially coherent x-ray wavefront propagation simulation software packages, namely, SHADOW and Synchrotron
Radiation Workshop (SRW). For SHADOW, we employed an SRW-generated source file which simulated spectralangular
distribution and apparent source characteristics of radiation produced by a 2.8 m long IVU with a 23 mm period
and allowed us to realistically estimate the beam intensity at the sample positions. We highlight the necessity to use
realistic mirror surface profiles with expected slope errors as opposed to “standard” built-in SHADOW surface error
options. The beamline performances at three different x-ray photon energies: 20358 eV, 10778 eV, and 2101 eV, under
different focusing conditions, have been studied. We compare beamline simulations performed with both software
packages. In particular, we stress that the neglect of wavefront diffraction effects in geometrical ray-tracing approach
results in significant discrepancies in beam spot size and beam shape, the correct assessments of which are crucial in
determining the future performance of an instrument.
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