[Nexus] Polarisation

[Tobias.Richter at diamond.ac.uk]

Hi all,

I am meeting some unexpected problems recording the polarisation of the incoming beam. 
All I could find is in NXbeam:

      final_polarization:NX_FLOAT[2,j]
      incident_polarization:NX_FLOAT[2,j]

There is no further clue about either the 2 or what j is. The values are float and units are NX_ANY. Hmm?

In any case I guess I would struggle to record circular polarisation in this scheme. Or is someone up for the challenge to explain that to me. 

The most natural feeling thing for someone with a vague optical background (reda: me) would be to use the 4 Stokes parameters. 

So I assume I propose to change that 2 to 4 (optionally) in the existing NXbeam. 
I'd prefer a [j,4] (transposed) array for these values.

Leaves the question what j is. There is an i index sprinkled into that class as well, but I am not sure how they are supposed to line up. Any one?

Regards,

Tobias

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