14.44  The Lens_simple McStas Component

Rectangular/circular slit with parabolic/spherical LENS.

Identification

• Author: Henrich Frielinghaus

• Origin: FZ Juelich

• Date: June 2010

Description

A simple rectangular or circular slit. You may either specify the radius (circular shape), or the rectangular bounds. No transmission around the slit is allowed.

At the slit position there is/are also a LENS or multiple LENSES present. Spherical/parabolic abberation is taken into account in a simplified manner. The focal point becomes a function of the distance ss from the origin of the lens where the ray hits the lens (plane). With this focal distance the refraction is calculated based on simple geometrical optics (as tought already in school).

The approximation gets wrong when the distance ss is too big, and total reflection becomes possible. Then the corrections of the focal distance are strong (see foc*= ... lines. When this correction factor is too close to zero, the corrections become highly wrong).

The advantage of this routine is the simplicity which makes the simulation very fast - especially for multiple lenses. The argument for this way of treating the lenses is that the collimation and detector distance are large (say 20m) compared to the lens thickness (say 2-5cm) and the lens array thickness (say max. 1m).

For lens arrays one still can simulate several of these simplified lenses instead of an exact treatment (because 5cm<<1m). The author believes that this medium detailed treatment meets usually the desired accuracy.

Example: Lens_simple(rho=5.16e10,Rc=0.0254,Nl=7,xmin=-0.01,xmax=0.01,ymin=-0.01,ymax=0.01) Lens_simple(rho=5.16e10,Rc=0.0254,Nl=7,radius=0.01) Lens_simple(rho=5.16e10,Rc=0.0254,Nl=7,radius=0.035,SigmaAL=0.141, d0=0.002) ^^^^^^^^^^^ last example includes absorption of MgF2-lens.

Input parameters

Parameters in boldface are required; the others are optional.

Links

• Component source code found in file Lens_simple.comp.