[Ifeffit] Chi(E) data export and import
bravel at bnl.gov
Fri Apr 1 07:25:07 CDT 2016
On 04/01/2016 07:58 AM, Matteo Busi wrote:
> Now for my master thesis, I'm performing a correction to chi(E) in the E
> space regarding to some geometrical properties of the sample.
> I have also tried to re-import the corrected data as a chi(k), having
> reproduced the right k grid column, but it looks totally wrong.
> The thing I'm not sure about is if the chi(E) needs to be fourier
> trasnformed into chi(k) or not.
> That's because I would have liked to make comparison in the Athena
> software between the two chis, but if that's not possible I will keep it
> to the external software (mathematic) with which the correction is
> Or if you can share me the fourier transform routine performed I can
> include it to my correction script.
You seem to be thinking about this wrongly. The chi(E) that gets
written to the mu(E) ascii file using the thing we discussed last time is
mu(E) - bkg(E)
That's it. The difference between the chi(E) in the mu(E) file and the
normal chi(k) is that (mu(E)-bkg(E)) is interpolated onto a uniform
k-grid. There are at least two reasons for doing that, (1) every data
sets then ends up on the same k-grid, which is a convenience, and (2) a
uniform k-grid allows use of a /fast/ Fourier transform.
If you want to overplot chi(E) and chi(k), you also have to do the
coordinate transform between energy and wave-number, which depends upon
the value of E0.
You have never clearly explained what you are up to and why
interpolating the normal chi(k) back onto the energy grid was
inadequate, so I don't know what else I can say that would be helpful.
Bruce Ravel ------------------------------------ bravel at bnl.gov
National Institute of Standards and Technology
Synchrotron Science Group at NSLS-II
Upton NY, 11973
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