About McXtrace
Publications
Project Partners
Project People
Goal
Documentation
Manual
Commands
Wiki (GitHub)
Tutorial
4.2 The Slit McXtrace Component
Rectangular/circular slit
Identification
-
Author: Erik Knudsen
-
Origin: DTU Physics
-
Date: June 16, 2009
Description
Based on Slit-comp by Kim Lefmann and Henrik Roennow A simple rectangular or circular slit. You may either specify the radius (circular shape), which takes precedence, or rectangular bounds. No transmission around the slit is allowed.
Example: Slit(xmin=-0.01, xmax=0.01, ymin=-0.01, ymax=0.01) Slit(radius=0.01)
Input parameters
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
|
|
|||
|
xmin |
m |
Lower x bound. |
0 |
|
xmax |
m |
Upper x bound. |
0 |
|
ymin |
m |
Lower y bound. |
0 |
|
ymax |
m |
Upper y bound. |
0 |
|
radius |
m |
Radius of slit in the z=0 plane, centered at Origin. |
0 |
|
xwidth |
m |
Width of slit. Overrides xmin,xmax. |
0.001 |
|
yheight |
m |
Height of slit. Overrides ymin,ymax. |
0.001 |
|
dist |
m |
Distance from slit plane to plane containing resampling target. |
0 |
|
focus_xw |
m |
Width of resampling window. |
0 |
|
focus_yh |
m |
Height of resampling window. |
0 |
|
focus_x0 |
m |
Centre (x) of resampling window. |
0 |
|
focus_y0 |
m |
Centre (y) of resampling window. |
0 |
|
|
|||
|
|
|||
|
|
|||
Links
-
Component source code found in file Slit.comp.
A beam defining diaphragm
The component Slit is a very simple construction. It sets up an opening at \(z=0\), and propagates the photon rays onto this plane (by the kernel call PROP_Z0). Photons within the slit opening are unaffected, while all other photons are discarded by the kernel call ABSORB.
By using Slit, some photons contributing to the background in a real experiment will be neglected. These are, for instance, the ones that scatter off the inner side of the slit, penetrate the slit material, or clear the outer edges of the slit.
The opening of the slit is determined by specifying either a radius, a width (xwidth) and a height (yheight), or absolute limits in \(x\) and \(y\) (xmin, xmax, ymin, ymax), in order of precedence. If radius is set, the opening is considered circular.
Slit may be used to model slit diffraction, thourgh judicious use of the resmapling parameters: focus_xw,focus_yh, focus_x0, focus_y0. The similarity in parameter naming for sources (chapter 3) is intentional as computationally the processes are the same. If present the focus parameters cause the ray to be regarded as a Huygens wave and a new direction going towards the resampling window is computed. The resulting difference in phase gives rise to maxima and minima as expected. This feature should be used with care: the further away from the optical axis, the more statistics and finer binning is needed to get meaningful results. Please refer to [BK+13] for more deatils.
