[NeXus-committee] Additions to NeXus

Wed May 11 14:09:38 BST 2016

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>
>> 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>
>>>
>>> o   *name*: *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>
>>>
>>> §  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>
>>>
>>> o   *name*: *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>  {units=
>>> *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>*[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>
>>>
>>> §  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>
>>> 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
>>> DECTRIS Ltd. | Taefernweg 1 | 5405 Baden-Daettwil | Switzerland |
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>>>
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