[mcxtrace-users] improved perfect crystal model

[Erik B Knudsen]

Dear Marcus,

Great news! We (as in the McXtrace team) would be happy study this 
improved crystal model, and to include this greatly improved crystal 
model in the official distribution, if that is your wish.

If you want, we'll be happy to assist you with your plans for a bent 
crystal model.

on behalf of the McXtrace team
Erik B Knudsen

On 05/10/15 14:00, Mendenhall, Marcus wrote:
> My group at NIST does extensive work with high-quality single-crystal
> optics to make xray spectrometers.  Using the "PerfectCrystal.comp"
> component turned up numerous computational errors and shortcomings in
> the model.
>
> I have taken the code from it, and both fixed the errors in it, and
> extended it to be more useful in a practical context.  This code should
> still look quite familiar to someone who has read the original
> PerfectCrystal.comp model.
>
> The issues fixed are:
>
> 1) rays with non-zero kx were reflected incorrectly
> 2) complex arithmetic in DarwinReflectivity had errors
> 3) atomic motion not handled at all, so rocking curve width was not right.
>
> The extensions are:
> 1) now fully handles polarization.  If ray comes in with Ex and Ey
> correctly defined, the outgoing polarization is a correctly computed
> from these. If Ex and Ey are zero on entrance, a new, random,
> polarization is generated, and then properly reflected.  If multiple
> bounces are used, the polarization propagates correctly.
> 2) added a crystal_type field which allows one to select diamond, bcc,
> or fcc cubic structures, or to explicitly provide the phase factors from
> which to compute form factors
> 3) added a field for the Debye-Waller temperature factor, and scaling of
> structure factors for the atomic motion.  Rocking curves now agree in
> high detail both with XOP and with our own experimental data.
>
> I have spent considerable effort validating the entire result.  I think
> this is a good representation of a flat, perfect crystal under realistic
> conditions.
>
>
> Anyone who has been using the PerfectCrystal.comp object, I would
> appreciate it if you would take a hard look at this and let me know if
> you see issues.  This should eventually probably turn up in the official
> McXtrace distribution.
>
> For the future:  I will extend this to handle bent crystals, to that
> Johansson monochromators can be modeled.
>
> Marcus Mendenhall
>
> Materials Measurement Science Division
> National Institute of Standards and Technology
> 100 Bureau Dr. stop 8370 (217/B115)
> Gaithersburg MD 20899 USA
> phone: +1(301) 975-8631
>
>
>
> _______________________________________________
> mcxtrace-users mailing list
> mcxtrace-users at mcxtrace.org
> http://mailman.mcxtrace.org/cgi-bin/mailman/listinfo/mcxtrace-users
>

-- 
Erik Bergbäck Knudsen, Research Engineer         | DTU | morituri
NEXMAP, DTU Fysik, DK-2800 Kgs. Lyngby, Denmark  |<>-<>|    te
phone: (+45) 2132 6655                           |<>-<>| salutant