xaid_calib
Module characteristics
- Goal: to calibrate a XAFS spectrum
Mu(x). Calibration is done by calculating Mu(Energy), where
the energy is calculated as a second degree polynomial in x. In
other words, this module helps in finding the a,b,c coefficients
in:
Energy_eV[i] = a+b*(x[i]-x[0])+c*(x[i]-x[0])^2
being i the index of the i-th point. (The substraction
of x[0] is essential for TurboXAS
experiments performed in ESRF/ID24 beamline).
- Method: Display the
reference spectrum and the spectrum to calibrate in a plotting window.
Change interactively the parameters. x[0] and a can be automatically calculated
via the computation of the spectra inflexion points.
-
Input: Two files:
- A 2 column file with calibrated spectrum (reference file) Mu(Energy_in_eV).
- A 2 column file with spectrum to calibrate Mu(x).
- Output: The a,b,c coefficients
and x[0]
Example of use
- Open the main window

- Load two files, the first one
with the reference spectrum and the second other with the spectrum to
calibrate. As examples, use the files Ge_calib.chi and Ge_calib.chi in
the Example directory. This may be done just by clicking the button

- You may plot the loaded files using the
button close to the file name.
- Click the button
to guess the initial values of x[0]
and a using by calculating the
spectra inflexion points. A new graphical window appears with the reference
spectrum and the spectrum to calibrate:

- Change b manually with the expansion compression value.
In the example, it can be estimated that the dashed spectrum must compress
at least 20 times to fit the solid one, so we put .05 in b
(do not forget to press
ENTER for refreshig the plot):

- Then improve the b value
by fine tuning using the
buttons. You may change the step of the
movement. You may also zoom in the plotting window for better looking.
- Sometimes the heights of the two spectra are very different, avoiding
a good overlapping. In such a case, the Y axis can be expanded (and shifted)
using the controls
.
Note that this option helps in visualizing the fine tuning but it does
not affect the resulting coefficients
- A result may be this one:

The resulting parameters may be copied to another program. They are
automatically passed to DELIA in the case that
XAID_CALIB is called from DELIA.