I believe that this is now a proper comparison. It is looking at the data that is from the

1. same fiber
2. very similar wavelength
3. very similar positions on the detector
4. same illumination (F/3.2)
5. the complete flux in the line from each arc are very similar. Neon is composed from 30 images, and HgAr from 3 images.

I am also showing 1d plots, which are done by horizontal or vertically summing all the flux in the image. You can see the difference in the vertical direction, even though there is no much difference in the horizontal direction! For completeness I am also adding 2d image.

Talked briefly with Jim. Asked me to check the line list just to make sure that there is no structure in the lines, and to confirm the effect in few spots near by.

After further analysis, I now see that wide wings are present in the Argon lines which exhibit the same lower transition state. I have extracted all of the lines which correspond to the that lower transition state (by using https://physics.nist.gov/PhysRefData/ASD/lines_form.html) and they all have the same profile. All other lines, even if they are very close on the detector (only few nanometer further) do NOT exhibit this widening.

I am attaching 2 figures:

1.

which shows the difference in the line profiles. Full lines correspond to the same lower transition state which shows brodening, and dashed lines denote all other transitions which do not show brodening.

2.

which shows the NIST output for this specific transition that is broad.

I will talk to Jim on how exactly to proceed. I am closing this now and further actions will be capture in following tickets.