# Module XAID_FF

## Module characteristics

- Goal: to calculate the Fourier Transform (FT) of a XAFS spectrum Chi(k) and the Back Fourier Transform (BFT) of a selected region of the FT. Chi(k) can be weighted with powers of k (from 0 to 4) and many weighting windows are available.
- Input: A 2 column file with Chi(k) data. It may also receive data from other XAID modules.
- Output: A SPEC-formatted data file with signal, FT and BFT (Use File->Save File).
- Tricks:
  - After changing any parameter, press "Enter" to refresh calculations.
  - The syntax of the intervals is: [min,max]. The square brackets and the separating coma are must always be entered.

## Follow the steps

1. Load a 2-colums ASCII file with input data (k in A in the first column and Chi(k) in the secondone) by using the File->Load File menu. Use for example the file: Ge_calib.chi.
2. Input:
   - The k limits for the FT (in left window)
   - The R interval in central window (limits for the FT plot).
   - The R limits for the Back Fourier (in central window). The BFT is calculated from the FT within these limits in R. The selected limits appear as vertical lines in the FT window (central window). This helps to select more accurately the wanted limits, normally including one or several peaks in the FT.
   - The k limits for the congugated variable (BFT in the right window). Note that this interval must be smaller than the "k limits for the Fourier Transform" interval in the left window, otherwise some numerical inconsistences appear.
   - The "Shell radius rfor the back phase". This affects only the BFT phase. The BFT is written as A(k)*sin(2kr+Phi(k)). The phase is Phi(k).
3. Press Enter for calculating and updating the windows after entering any new parameter. See an example window.

## FAQs

- Can I load a scan from a SPEC file in XAID_FF?
  Not directly. You can however open Xplot (e.g., Tools->Xplot, load your SPEC data file in Xplot, and start XAID_FF with your selected scan from the Xplot Calculations->XAFS->Xafs Extraction (xaid_ff)

## Window example

(click on the image for full resolution)

[Back]