<div dir="ltr"><div>Dear Ben,<br><br></div> 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:<br><span style="font-family:arial,helvetica,sans-serif"><br></span><font color="#000000"><pre><span style="font-family:arial,helvetica,sans-serif">/incident_polarisation_stokes_average=[SVECI,SVECQ,SVECU,SVECV]</span><span style="font-family:arial,helvetica,sans-serif"><font color="#000000"><pre><font face="arial,helvetica,sans-serif"> </font>@units="Watts/meter^2"</pre></font></span><span style="font-family:arial,helvetica,sans-serif"></span><span style="font-family:arial,helvetica,sans-serif"></span><span style="font-family:arial,helvetica,sans-serif"> /incident_polarisation_stokes=[STOKESI,STOKESQ,STOKESU,STOKESV]
</span><font color="#000000"><pre><span style="font-family:arial,helvetica,sans-serif"> @units="Watts/meter^2"<br><br></span></pre><pre><span style="font-family:arial,helvetica,sans-serif">So that we can carry frame-by-frame polarization if we have it, or just <br>the average if we don't.</span><br></pre></font></pre></font></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 11, 2016 at 9:09 AM, Benjamin Watts <span dir="ltr"><<a href="mailto:benjamin.watts@psi.ch" target="_blank">benjamin.watts@psi.ch</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
Hi Everyone,<br>
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". <br>
<br>
* 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.<br>
* The 'i' and 'j' symbols seems inconsistent on
<a href="http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html" target="_blank">http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html</a>
Perhaps it is supposed to allow multiple incoming and outgoing
beams, but it got messed up along the way.<br>
<br>
Cheers,<br>
Ben<div><div class="h5"><br>
<br>
<br>
<div>On 11/05/16 14:50, Eugen Wintersberger
wrote:<br>
</div>
<blockquote type="cite">
Hi Pete<br>
<br>
<div>On 05/11/16 13:33, Pete Jemian wrote:<br>
</div>
<blockquote type="cite">
<pre>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.</pre>
</blockquote>
Besides the fact that NXbeam is mentioned as a possible child for
NXsample<br>
it makes perfect sense there too. <br>
If you have many optical components in your beam path and one is
mainly interested in the <br>
beam paramters in front of the sample NXbeam within NXsample would
be my <br>
first approach to document these parameters.<br>
<br>
regards<br>
Eugen<br>
<br>
<br>
<blockquote type="cite">
<pre>Pete
On May 11, 2016 6:17 AM, "Andreas Förster" <a href="mailto:andreas.foerster@dectris.com" target="_blank"><andreas.foerster@dectris.com></a>
wrote:
</pre>
<blockquote type="cite">
<pre>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*
<a href="http://download.nexusformat.org/sphinx/classes/base_classes/NXsource.html" target="_blank"><http://download.nexusformat.org/sphinx/classes/base_classes/NXsource.html></a>
o *name*: *NX_CHAR*
<a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char></a>
§ Name of synchrotron
o *@short_name*: *NX_CHAR*
<a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char></a>
§ 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*
<a href="http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html" target="_blank"><http://download.nexusformat.org/sphinx/classes/base_classes/NXbeam.html></a>
o *name*: *NX_CHAR*
<a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char></a>
§ Name of beamline
o *total_flux/xray_flux*: *NX_FLOAT*
<a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float></a> {units=
*NX_RATE* <a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-rate" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-rate></a>
}
§ Beam intensity (example: s-1)
o *incident_beam_size: **NX_FLOAT*
<a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-float></a>*[2]*
§ Two-dimensional array of FWHM (if Gaussian) or diameters (if top hat)
of beam
o *profile*: *NX_CHAR*
<a href="http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char" target="_blank"><http://download.nexusformat.org/sphinx/nxdl-types.html#nx-char></a>
§ 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
--
<a href="https://www.dectris.com" target="_blank"><https://www.dectris.com></a>
Andreas Förster, Ph.D.
MX Application Scientist, Scientific Sales
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