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Discrepancy between excitation profiles of the sinc fucntion
Posted: Thu Oct 07, 2021 8:27 am
by Khalil
Dear EasySpin users,
I am interested in looking to shaped pulses and particularly to the sinc function. However when using easyspin functions to calculate the excitation profile it did shows some sharp spikes. However, when I did manually calculate the inversion profile these spikes disappear. I know in my case I did a simple fft to calculate the excitation profile but I am wondering if these spikes are real. I have attached the script and the associated figure.
Any thoughts??
Regards
Re: Discrepancy between excitation profiles of the sinc fucntion
Posted: Thu Oct 07, 2021 9:05 am
by Stefan Stoll
There is a reason for the discrepancy: the FFT is a linear operation, whereas spin dynamics (Bloch equations) is fundamentally nonlinear. So taking the FFT is only an approximation. In the limit of small flip angles, this approximation works well. You can see this by reducing Par.Flip in your script. For flip angles like pi/2 or pi, the approximation breaks down, and one really needs to solve the Bloch equations, as is done by EasySpin.
Re: Discrepancy between excitation profiles of the sinc fucntion
Posted: Fri Oct 08, 2021 1:51 am
by Khalil
Many thanks Stefan.
Regards