*
* Perfect, laue crystal with common cubic structures (diamond, fcc, or bcc, and others if symmetry form factor multipliers provided explicitly)
*
*

Identification

Site:

Author: Marcus H Mendenhall, NIST

Origin: Marcus H. Mendenhall, NIST, Gaithersburg, MD, USA

Date: June, 2017

Description

* NIST_Laue_crystal_BC.comp is written by Marcus H. Mendenhall, NIST, Gaithersburg, MD, USA
* It is based on the full vector math and exact solution of the dispersion relation in
* Batterman and Cole, Reviews of Modern Physics 36 number 3, page 681, July 1964
* Non-copyright notice:
* Contributed by the National Institute of Standards and Technology; not subject to copyright in the United States.
* This is not an official contribution, in that the results are in no way certified by NIST.
* Perfect crystal with common cubic structures (diamond, fcc, or bcc, and others if symmetry form factor multipliers provided explicitly)
*
* Reads atomic form factors from a data input file.
* The Laue_Crystal code reflects rays in an ideal geometry, does not include surface imperfections or mosaicity.
*
* The crystal is positioned such that the long axis of the crystal surface coincides with
* z-axis and the outer normal to the crystal surface is along +y.
*
* The ratio of the transmitted beam and forward-diffracted Borrman-effect beam is a hack. The sum of the
* two is exactly right, but the actual ratio depends critically on geometry, and I just put in a wild estimate
* to allow one to demonstrate what the Borrmann effect looks like. If this is turned on, the displacement of the
* transmitted beam and forward diffracted beam at the back side of the crystal will be correctly computed.
* This displacement is only exact for symmetrical Laue; asymmetrical computation requires more effort,
* and is probably not worth it.
* The sampling of these processes are controlled by the 3 variables transmission_sampling, forward_diffraction_sampling,
* and laue_sampling. Since 99% of uses of this will have the transmitted beam turned off, and use laue diffraction mode,
* the values should be just 0,0,1. If the general behavior of the transmitted beams
* is interesting, use 1,1,1 which samples all beams equally. Results weights are adjusted for this,
* so computed intensities won't be affected.
*
*
*
*

Input parameters

Parameters in boldface are required;
the others are optional.

Name

Unit

Description

Default

length

0.05

width

0.02

thickness

1e-4

V

160.1826

form_factors

"FormFactors.txt"

material

"Si.txt"

alphax

0.0

alphay

0.0

alphaz

1.0

debye_waller_B

0.4632

crystal_type

1

h

1

k

1

l

1

structure_factor_scale_r

0.0

structure_factor_scale_i

0.0

transmission_sampling

1.0

forward_diffraction_sampling

1.0

laue_sampling

1.0

Output parameters

Parameters in boldface are required;
the others are optional.