Module 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).
- 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 (displayed in main
window).
- Tricks:
- Remember you always move the dashed (calibrated) plot, and the
continous (reference) remains fixed.
Follow the steps
- From the main window (see Example window 1), 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,
respectively. Once both spectra are loaded, an auxiliar XPLOT window
(see Example window 2) appears. An estimated a value appears
automatically.
- Change b manually with the expansion compression value.
In the example, I estimate that the dashed spectrum must compress
at least 20 times to fit the solid one, so I put .05 in b and
then I do not forget to press ENTER for refreshig the
plot.
- Change a manually to a better estimation. You can estimate
the value that the edge of the dashed (calibrated) spectrum must
move to align to the continuous (reference) spectrum by using the
(x,y) cursor position in the XPLOT window. In the example, I
estimate that it should be moved 200 units (11100-10900) to the
right, so I changed a from 10800 (initial guess) to 11000.
And then I do not forget to press ENTER for refreshig the
plot.
- Then I click on the a button, and fine tunning the
a value using the "<<" and ">>" buttons. You may change the
step of the movement.
- Then I click on the b button, and do the fine tunning.
I may neede iterating a and b tunning. It may also
be necessary to use the non-linear term c.
- Occasionaly, the heigth of the twe spectra is different avoiding
a good overlapping. For that you can expand the Y axis using the
value "Expansion ratio of Y axis". This helps in the fine tunning
but does not affect the resulting coefficients.
- A calibration (not exceptional) is shown in example window 3.
Window example
Window 1: Main window after loading the two example files.
Window 2: XPlot auxiliar window after loading the two example files.
(click on the images for full resolution)
Window 3: XPlot auxiliar window with a result of calibration process.
FAQs
- May I zoom the image and fix the limits to the zoomed area?
Yes. Just select the wanted area to zoom, click the Zoom
button and go to Edit->Limits->Set Limits as Selection
Area. The next plots will be displayed in the selected area.
To go back to the defaults, go to
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