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McStas: Lens Component

[ Identification | Description | Input parameters | Output parameters | Links ]

The Lens Component

Refractive lens with absorption, incoherent scattering and surface imperfection.


  • Author: C. Monzat/E. Farhi/S. Desert/G. Euzen
  • Origin: ILL/LLB
  • Date: 2009
  • Version:(Unknown)


Refractive Lens with absorption, incoherent scattering and surface imperfection.
Geometry may be:
  spherical (use r1 and r2 to specify radius of curvature),
  planar    (use phiy1 and phiy2 to specify rotation angle of plane w.r.t beam)
  parabolic (use focus1 and focus2 as optical focal length).

Optionally, you can specify the 'geometry' parameter as a OFF/PLY file name.
  The complex geometry option handles any closed non-convex polyhedra.
  It computes the intersection points of the neutron ray with the object
  transparently, so that it can be used like a regular sample object.
  It supports the PLY, OFF and NOFF file format but not COFF (colored faces).
  Such files may be generated from XYZ data using:
    qhull < Qx Qv Tv o >
  and viewed with geomview or java -jar jroff.jar (see below).

The lens cross-section is seen as a 2*radius disk from the beam Z axis, except
  when a 'geometry' file is given.
Usually, you should stack more than one of these to get a significant effect
on the neutron beam, so-called 'compound refractive lens'.

The focal length for N lenses with focal 'f' is f/N, where f=R/(1-n)
  and R = r/2   for a spherical lens with curvature radius 'r'
      R = focus for a parabolic lens with focal of the parabola
  and n = sqrt(1-(lambda*lambda*rho*bc/PI)) with
    bc  = sqrt(fabs(sigma_coh)*100/4/PI)*1e-5
    rho = density*6.02214179*1e23*1e-24/weight

Common materials: Should have high coherent, and low incoherent and absorption cross sections
  Be:            density=1.85,  weight=9.0121, sigma_coh=7.63,  sigma_inc=0.0018,sigma_abs=0.0076
  Pb:            density=11.115,weight=207.2,  sigma_coh=11.115,sigma_inc=0.003, sigma_abs=0.171
    Pb206:                                     sigma_coh=10.68, sigma_inc=0    , sigma_abs=0.03
    Pb208:                                     sigma_coh=11.34, sigma_inc=0    , sigma_abs=0.00048
  Zr:            density=6.52,  weight=91.224, sigma_coh=6.44,  sigma_inc=0.02,  sigma_abs=0.185
    Zr90:                                      sigma_coh=5.1,   sigma_inc=0    , sigma_abs=0.011
    Zr94:                                      sigma_coh=8.4,   sigma_inc=0    , sigma_abs=0.05
  Bi:            density=9.78,  weight=208.98, sigma_coh=9.148, sigma_inc=0.0084,sigma_abs=0.0338
  Mg:            density=1.738, weight=24.3,   sigma_coh=3.631, sigma_inc=0.08,  sigma_abs=0.063
  MgF2:          density=3.148, weight=62.3018,sigma_coh=11.74, sigma_inc=0.0816,sigma_abs=0.0822
  diamond:       density=3.52,  weight=12.01,  sigma_coh=5.551, sigma_inc=0.001, sigma_abs=0.0035
  Quartz/silica: density=2.53,  weight=60.08,  sigma_coh=10.625,sigma_inc=0.0056,sigma_abs=0.1714
  Si:            density=2.329, weight=28.0855,sigma_coh=2.1633,sigma_inc=0.004, sigma_abs=0.171
  Al:            density=2.7,   weight=26.98,  sigma_coh=1.495, sigma_inc=0.0082,sigma_abs=0.231
                 density=2.2,   weight=50.007, sigma_coh=13.584,sigma_inc=0.0026,sigma_abs=0.0227
  Organic molecules with C,O,H,F

Example: Lens(r1=0.025,r2=0.025, thickness=0.001,radius=0.0150)

parabolic shape is not fully validated yet, but should do still...

WARNING: This is a contributed Component.

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
r1 m radius of the first circle describing the lens. r>0 means concave face, r<0 means convex, r=0 means plane 0
r2 m radius of the second circle describing the lens r>0 means concave face, r<0 means convex, r=0 means plane 0
focus1 m focal of the first parabola describing the lens 0
focus2 m focal of the second parabola describing the lens 0
phiy1 deg angle of plane1 (r1=0) around y vertical axis 0
phiy2 deg angle of plane2 (r2=0) around y vertical axis 0
thickness m thickness of the lens between its two surfaces 0.001
radius m radius of the lens section, e.g. beam size. 0.015
sigma_coh barn coherent cross section 11.74
sigma_inc barn incoherent cross section 0.0816
sigma_abs barn thermal absorption cross section 0.0822
density g/cm3 density of the material for the lens 3.148
weight g/mol molar mass of the material 62.3018
p_interact 1 MC Probability for scattering the ray; otherwise transmit 0.1
focus_aw deg vertical angle to forward focus after scattering 10
focus_ah deg horizontal angle to forward focus after scattering 10
RMS Angs root mean square roughness of the surface 0
geometry str Name of an Object File Format (OFF) or PLY file for complex geometry. The OFF/PLY file may be generated from XYZ coordinates using qhull/powercrust 0

Output parameters

Name Unit Description Default


  • Source code for Lens.comp.
  • M. L. Goldberger et al, Phys. Rev. 71, 294 - 310 (1947)
  • Sears V.F. Neutron optics. An introduction to the theory of neutron optical phenomena and their applications. Oxford University Press, 1989.
  • H. Park et al. Measured operationnal neutron energies of compound refractive lenses. Nuclear Instruments and Methods B, 251:507-511, 2006.
  • J. Feinstein and R. H. Pantell. Characteristics of the thick, compound refractive lens. Applied Optics, 42 No. 4:719-723, 2001.
  • Geomview and Object File Format (OFF)
  • Java version of Geomview (display only) jroff.jar
  • qhull
  • powercrust

[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <> / Wed Jan 12 15:13:31 2022

Last Modified: Wednesday, 12-Jan-2022 16:13:31 CET
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