[NeXus-committee] Additions to NeXus

Wed May 11 15:31:51 BST 2016

Dear Ben,

  The two-component polarization has been customary in MX work for many
years, but you are absolutely right that a full Stokes vector would make
the most sense.  I would suggest two versions:

/incident_polarisation_stokes_average=[SVECI,SVECQ,SVECU,SVECV]

     @units="Watts/meter^2"

 /incident_polarisation_stokes=[STOKESI,STOKESQ,STOKESU,STOKESV]

       @units="Watts/meter^2"

So that we can carry frame-by-frame polarization if we have it, or just
the average if we don't.

On Wed, May 11, 2016 at 9:09 AM, Benjamin Watts <benjamin.watts at psi.ch>
wrote:

> Hi Everyone,
>    I'm going to agree with Eugen that it makes sense for NXbeam to be a
> child of NXsample as it implies that the beam is described at the position
> of the sample. If there are multiple sources as Pete described, then they
> can be differentiated by the name of the NXbeam group being "pump" and
> "probe".
>
> * It would also be useful to better specify the "polarisation vector" for
> 'incident_polarization' and 'final_polarization' - I don't understand what
> this 2-component vector is supposed to be. I would suggest we use a Stokes
> vector.
> * The 'i' and 'j' symbols seems inconsistent on
> http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html
> Perhaps it is supposed to allow multiple incoming and outgoing beams, but
> it got messed up along the way.
>
> Cheers,
> Ben
>
>
>
> On 11/05/16 14:50, Eugen Wintersberger wrote:
>
> Hi Pete
>
> On 05/11/16 13:33, Pete Jemian wrote:
>
> The source is definitely a part of the instrument, not something at the top
> level of the experiment (NXentry). Consider the case of a synchrotron X-ray
> experiment with a laser pump.  There are two sources to be documented.
> They both belong under the description of the pump/probe instrument.
>
> Why should the beam be part of the sample? Makes no sense at all.  The
> sample has no beam.  The beam does not describe the sample in any useful
> way.  NXbeam documents the state of the beam at some position along the
> path from source to detector.  It could go in many places along the optical
> path.
>
> Besides the fact that NXbeam is mentioned as a possible child for NXsample
> it makes perfect sense there too.
> If you have many optical components in your beam path and one is mainly
> interested in the
> beam paramters in front of the sample NXbeam within NXsample would be my
> first approach to document these parameters.
>
> regards
>   Eugen
>
>
> Pete
> On May 11, 2016 6:17 AM, "Andreas Förster" <andreas.foerster at dectris.com> <andreas.foerster at dectris.com>
> wrote:
>
>
> Dear NeXus folks,
>
> there was a little discussion last week about possible additions to the
> NeXus standard (and NXmx) to record beam information relevant for the
> estimation of dose.  Herbert proposed a good solution, but the outcome of
> this discussion is still pending.
>
> At DECTRIS, we're keen to tell our customers how to record additional
> metadata in a NeXus-compliant way.  That's why I'd like to have official
> word on the fields below:
>
> Information on the synchrotron should be recorded in an NX_Source group.
> Is /entry/source the right place for that?
>
>      /entry/source *NX_SOURCE*<http://download.nexusformat.org/sphinx/classes/base_classes/NXsource.html> <http://download.nexusformat.org/sphinx/classes/base_classes/NXsource.html>
>
> o   *name*: *NX_CHAR*<http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char>
>
> §  Name of synchrotron
>
> o   *@short_name*: *NX_CHAR*<http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char>
>
> §  short name for source, perhaps the acronym
> Data describing the beam as it hits the sample should probably go the
> NX_Beam group in /entry/sample/beam.  None of the fields below are
> currently defined.  Could these definitions be adopted?
>
> ·      /entry/sample/beam *NX_BEAM*<http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html> <http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html>
>
> o   *name*: *NX_CHAR*<http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char>
>
> §  Name of beamline
>
> o   *total_flux/xray_flux*: *NX_FLOAT*<http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float> {units=
> *NX_RATE* <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-rate> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-rate>
> }
>
> §  Beam intensity (example: s-1)
>
> o   *incident_beam_size: **NX_FLOAT*<http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float>*[2]*
>
> §  Two-dimensional array of FWHM (if Gaussian) or diameters (if top hat)
> of beam
>
> o   *profile*: *NX_CHAR*<http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char> <http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char>
>
> §  Gaussian or top hat
>
> Should the name of the beamline be recorded in beam or in source?  For the
> flux (as a rate - in contrast to the already existing flux density field
> "flux"), either name is fine by me.
>
> I'm happy to discuss these points during the next NeXus meeting.
>
> Thank you and all best
>
>
> Andreas
>
>
>
> --<https://www.dectris.com> <https://www.dectris.com>
> Andreas Förster, Ph.D.
> MX Application Scientist, Scientific Sales
> Phone: +41 56 500 2100 | Direct: +41 56 500 2176 | Email:andreas.foerster at dectris.com
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