[Ifeffit] pi/2deltak

[Matt Newville]

Hi Riti,

On Sat, Jan 30, 2016 at 7:35 PM, Ritimukta Sarangi <ritimukta at gmail.com>
wrote:

> Hello,
>
> I was recently asked about the accuracy of this formulation for obtaining
> EXAFS resolution and I did not have a good answer. Can someone point to a
> reference or explain here?
>
Thank you for your time,
> Best,
> -Riti
>
>
The deltaR = pi / 2DeltaK  follows from general Fourier analysis and
formulas like it can be found in many signal processing textbooks.    For
on-line resources, googling "Frequency resolution Fourier transform" gives
several good references.

The idea is that (using sound-waves as an example) in order to distinguish
two close frequencies (say 440 Hz from 441 Hz, so a different of 1 Hz), you
have to sample many periods (pi seconds) to be able to do this.

For EXAFS, if there are contributions from two neighbors that are very
closely spaced, you would have to sample enough oscillations (go high
enough in k) to see the effect of these two different distances beating
against each other.   If you don't go out far enough in k,  you can't tell
that these two contributions are actually from different distances.

Hope that helps,

--Matt
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