Re: [Ifeffit] energy resolution
Hello all. I am getting confused with different comments how to determine the energy resolution of an XAS beamline. I think using peak fitting to determine the line width is a reasonable method. The basis of a XAS peak is the Voigt profile (a combination of a Lorenzian and Gaussian) The width of the Lorenzian equals the natural line width while the width of the Gaussian represents the experimental line width and some features Now here is question 1: What is the combination of the two profiles in the Athena peak fitting routine for the Pseudo-Voigt? Question 2: Is the sigma (Gaussian width) that delta E that represents the resolution - (E /delta E) ? Using a different program (Igor Pro) to determine the width gives different results because can only use a simple combination of Lorentz and Gauss (1:1). Thanks. Lisa
On 04/20/2015 12:01 PM, Lisa Bovenkamp wrote:
Now here is question 1: What is the combination of the two profiles in the Athena peak fitting routine for the Pseudo-Voigt?
Hi Lisa, Athena uses Ifeffit for this. Ifeffit's pseudo-Voight function is implemented here: https://github.com/newville/ifeffit/blob/master/src/lib/conv_lor.f#L314 (Larch's is explained here: http://xraypy.github.io/xraylarch/fitting/lineshapes.html) In Athena, gamma is the mixing parameter for the pseudo-Voight. That said, this might not be doing quite what you are looking for. Ifeffit's implementation uses the same width for both functions (as does Larch), which does not seem to be what you are asking for. I suppose you could try using two lineshapes, one Gaussian and one Lorentzian, which share a value for the centroid. That is possible in Athena as long as you don't float the centroids. While floating a common centroid is possible in both Ifeffit and Larch, there is no way to indicate that in Athena. I'm not sure off the top of my head how to interpret the amplitudes in that situation to extract a value equivalent to gamma. Perhaps Athena isn't the right tool for the job? Or perhaps you can figure out something that does what you want using either Ifeffit or (preferably!) Larch? In that case, let me know and I'll see about including it in Athena. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/
participants (2)
-
Bruce Ravel -
Lisa Bovenkamp