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xrt 0.9.1

Ray tracing in x-ray regime, primarily meant for modeling synchrotron beamlines and beamline elements

Package Documentation

Latest Version: 0.9.2

Package xrt (XRayTracer) is a python software library for ray tracing in x-ray regime. It is primarily meant for modeling synchrotron beamlines and beamline elements.

Why another ray tracing program?

Indeed, there are several good programs for ray tracing, like Shadow, Ray, McXtrace. These have been extremely useful in modeling synchrotron beamlines and/or individual beamline components. However, they all have the following drawbacks:

  • Limited graphical output, where the images are composed of dots representing individual rays. A color map, if ever implemented, can encode a physical property not weighted with intensity (unless it is intensity itself).
  • The choice of surface shapes is very limited. Closed shapes, like wave-guides or capillaries, are not possible.
  • Multiple reflections at a single surface, as it happens in a multi-bounce capillary, are not possible.
  • Non-sequential optical elements, as poly-capillaries or multi-mirror arrays, are not possible.
  • There are many restrictive limitations on energy range and energy mesh points, spatial mesh size etc.
  • The execution cannot be parallelized (except may be in McXtrace).

The above issues are resolved in xrt.

Features of xrt

  • Publication quality graphics. 1D and 2D position histograms are simultaneously coded by hue and brightness. Typically, colors represent energy and brightness represents beam intensity. The user may select other quantities to be encoded by colors: angular and positional distributions, various polarization properties, beam categories, number of reflections, incidence angle etc. Brightness can also encode partial flux for a selected polarization and incident or absorbed power. Publication quality plots are provided by matplotlib with image formats PNG, PostScript, PDF, SVG.
  • Unlimited number of rays. The colored histograms are cumulative. The accumulation can be stopped and resumed.
  • Parallel execution. xrt can be run in parallel in several threads or processes (can be opted), which accelerates the execution on multi-core computers. It can run on an external server (supercomputer), also without X window system (X11) support.
  • Scripting in Python. xrt can be run within Python scripts to generate a series of images under changing geometrical or physical parameters. The image brightness and 1D histograms can be normalized to the global maximum throughout the series.
  • Sources. xrt can have several light sources. For example, an ID beamline has 3 sources: one ID and two BM. This feature allows exploring the influence of out-of-focus sources.
  • Synchrotron sources. Bending magnet, wiggler, undulator and elliptic undulator are calculated internally within xrt (new in version 0.9). There is also a legacy approach to sampling synchrotron sources using the codes ws and urgent which are parts of XOP package. Please look the section Comparison of synchrotron sources for the comparison between the two implementations. If the photon source is one of the synchrotron sources, the total flux in the beam is reported not just in number of rays but in physical units of ph/s. The total power or absorbed power can be opted instead of flux and is reported in W. The power density can be visualized by isolines.
  • Shapes. There are several predefined shapes of optical elements implemented as python classes. The inheritance mechanism simplifies creation of other shapes. The user specifies methods for the surface and the surface normal. For asymmetric crystals, the normal to the atomic planes can be additionally given. The surface and the normals are defined either in local (x, y) coordinates or in user-defined parametric coordinates. Parametric representation enables closed shapes like capillaries. The methods of finding the intersections of rays with the surface are very robust and can cope with pathological cases like sharp surface kinks. Any surface can be combined with a (differently and variably oriented) crystal structure and/or (variable) grating vector. Surfaces can be faceted.
  • Energy dispersive elements. Implemented are crystals in dynamical diffraction, gratings (so far, without efficiency calculations), Fresnel zone plates and Bragg-Fresnel optics. Crystals can work in Bragg or Laue cases, in reflection or in transmission. The two-field polarization phenomenaare fully preserved, also within the Darwin diffraction plateau, thus enabling the ray tracing of crystal-based phase retarders. As compared to XOP/Shadow, xrt works correctly for asymmetric crystals in transmission regime.
  • Materials. The material properties are incorporated using three different tabulations of the scattering factors, with a wide energy range (>100 keV) or finer energy mesh. Refraction index and absorption coefficient are calculated from the scattering factors. Two-surface bodies, like plates or refractive lenses, are treated with both refraction and absorption.
  • Multiple reflections. xrt can trace multiple reflections in a single optical element. This is useful, for example in 'whispering gallery' optics or in Montel or Wolter mirrors. Here, very handy is the histogramming over the number of reflections, incidence angle and elevation over the surface.
  • Non-sequential optics. xrt can trace non-sequential optics where different parts of the incoming beam meet different surfaces. Examples of such optics are poly-capillaries and Wolter mirrors.
  • Global coordinate system. The optical elements are positioned in a global coordinate system. This is convenient for modeling a real synchrotron beamline. The coordinates in this system can be directly taken from a CAD library. The optical surfaces are defined in local systems for the user's convenience.
  • Beam categories. xrt discriminates rays by several categories: good, out, over and dead. This distinction simplifies the adjustment of entrance and exit slits. An alarm is triggered if the fraction of dead rays exceeds a specified level.
  • Portability. xrt runs on Windows and Unix-like platforms, wherever you can run python.
  • Examples. xrt comes with many examples; see the gallery.


The histogramming is done by means of numpy; matplotlib is used for plotting.

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