Xraytrace documentation

To create the X-ray standing wave field we need to let the incoming rays to be totally reflected and get interfered with other incoming rays. We have different ways how the rays can be sourced:

Rays can be simply casted from a plane outside of the computational volume, hitting some interface in the computational volume where the total reflection condition is met and create the standing wave field. For small angles this however means to have really large computational volume. This is the simple source method and can be set by using the directive

SOURCE_METHOD
0

If we use this source method, we can play with the size of the incident beam. To increase or shrink the size of plane from which the rays are casted (i.e. to change the beam shape), the command like this can be used

SOURCEMULT
0.1 0.1 10

which here shrinks the beam in x and y and increases its size in z. The default beam size in source method 0 is governed by the COMP command (see Running the computation section).

An alternative source method is to cast rays from whole computational boundary at once, already assuming that it was totally reflected outside of it - so casting both rays propagating towards sample and mirrored rays. This is done in source method = 1.

Finally, we can use only the top boundary for casting the rays and let them to periodically repeat. This is the source method 3. In this case we artificially create the periodic boundary near to the computational domain boundary, on basis of the source wavelength. All the rays incoming to this boundary are transversed back to the start of the computational domain. Obviously, this case is suitable only for periodic samples. On the other hand, for such samples it is the only method that can reproduce the realistic behavior of the incoming rays.

The different source methods are illustrated on the figure below:

COHERENCE
integer double

- sets coherence on/off. Default is 0, meaning off. If coherence is switched on, all the rays have the same phase at the beginning and amplitudes are summed instead of intensities. Second parameter is the phase itself, in degrees.

PHASES
integer

- sets number of phases to use in calculation, directly prolongs the process. Default value is 1.

SOURCE_MATCUT
int

- cut source parts not illuminating given material index. 0, which is vacuum, means illuminate all.

SOURCEMULT
double double double

- multiplies apparent source radius in x, y and z direction to create elliptical shape.

SIMPLE
0/1

Run simple calculation according to Bedzyk, X-ray Standing wave techniques, assuming that material 2 is the reflecting one, and the XSW is in z. Material and data below surface plane have no meaning and are not evaluated.

MEGASIMPLE
0/1 matindex

Run megasimple calculation according to Bedzyk, X-ray Standing wave techniques, assuming that material 2 is the reflecting one, and the XSW is in z. Only single material is evaluated. Not all the vector commands work properly.