[ Identification | Description | Input parameters | Links ]

# The `Lens_simple` Component

Rectangular/circular slit with parabolic/spherical LENS.

## Identification

- Site:
- 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.

Name | Unit | Description | Default |
rho | m-2 | Scattering length density | 5.16e14 |
Rc | m | Radius (concave: Rc>0) of biconcave lens | 0.02 |
Nl | 1 | Number of single lenses | 7.0 |
parab |  | Switch (not 0 -> parabolic, for 0 spherical) | 1.1 |
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 |
SigmaAL |  | Absorption cross section per lambda (wavelength) [1/(m*AA)] | 0.141 |
d0 | m | Minimum thickness in the centre of the lens | 0.002 |

AT ( | , | , |  | ) RELATIVE |  |
ROTATED ( | , | , |  | ) RELATIVE |

## Links

- Source code for `Lens_simple.comp`.

[ Identification | Description | Input parameters | Links ]