[Ifeffit] Basic questions about the preliminary data processing in Athena

[Carlo Segre]

The calibration should be done at the beamline with a foil.  Once that is 
done, then you don't really want to change it.  Remember that just 
shifting the energy is not actually the correct way to do a shift.  The 
energy shift is a non-linear function of the angle (Bragg's Law) and so 
when you shift energy you are really distorting Chi(k) since that is also 
a non-linear function of energy (E^1/2).  Yes, it is usually a small 
effect but I prefer not to apply too many shifts in energy if possible.

I assume that the calibrate function is the same as the align except the 
E-shift is left at zero and a correction is applied permanently to the 
data.

Carlo

On Mon, 23 Jul 2018, Haifeng Li wrote:

> Hi, Carlo,
>
> Thanks for your answer.
>
> I may ask you more questions. Why you do not recommend to calibrate the
> data? Calibration is used to find the E0 and match it to the literature
> data. What is the real difference between calibration and alignment?
>
> Thanks,
>
> Haifeng
>
> On Sun, Jul 22, 2018 at 5:30 PM, Carlo Segre <segre at iit.edu> wrote:
>
>>
>> Hello Haifeng:
>>
>> Personally, I would not calibrate the data but merely align the references
>> of A2 and A3 to the reference of A1 and similarly align B2 and B3
>> references to that of B1.  Once merged, you can then aligh the reference of
>> the merged B samples to that of the merged A samples.
>>
>> If you keep the references then you can always align data taken at a leter
>> time to these data sets.  If the energy of your reference is a small bit
>> off from the tabulated value, that is OK as long as all the data being
>> compared has aligned references.
>>
>> Carlo
>>
>>
>> On Sun, 22 Jul 2018, Haifeng Li wrote:
>>
>> Dear ALL,
>>>
>>> I am a beginner in Athena. Recently I got the spectra and I am confusing
>>> about the data calibration and alignment. The manual shows that calibrate
>>> the reference data of one scan and align other reference data to that
>>> calibrated one.
>>>
>>> Here I want to show examples. I have two samples A and B, Each sample has
>>> three scans with the corresponding reference data. For sample A, 1st scan
>>> is calibrated and the other two scans are aligned to 1st scan. Then merge
>>> them into merged A. The same procedures for sample B and get merged B. If
>>> I
>>> want to compare XANES of sample A and B, do I need to align the merged
>>> reference data between A and B? If so, why? My understanding is that all
>>> scans (original data and merged data) in sample A and B are calibrated to
>>> standard edge energy. Why do they need to align?
>>>
>>> I appreciate your help.
>>>
>>> Thanks,
>>>
>>> Haifeng
>>>
>>>
>> --
>> Carlo U. Segre -- Duchossois Leadership Professor of Physics
>> Interim Chair, Department of Chemistry
>> Director, Center for Synchrotron Radiation Research and Instrumentation
>> Illinois Institute of Technology
>> Voice: 312.567.3498            Fax: 312.567.3494
>> segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org
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>

-- 
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Interim Chair, Department of Chemistry
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org