No echos from isotropic system in saffron
Posted: Mon Jan 27, 2025 3:15 am
Hello,
I am trying to get a handle on the basics of saffron. I took the 2p-echo example and tried to simplify it by removing the 14N nucleus and setting the g-tensor to a fully isotropic value (in particular 2.006).
What happens then is that the simulation seems to give an pattern that corresponds to the detuning frequency, and not to the echo itself. Indeed, if I then set the magnetic field precisely to the resonance value, I get two flat lines.
Is there an issue with calculating isotropic systems?
The modified script is:
Code: Select all
% Two-pulse echo transient using chirp pulses (saffron)
%==========================================================================
% Simulates a chirp echo of a nitroxide using saffron
clear; close all;
Exp.Field = 324.9; % mT
% Spin system
Sys.g = [2.006 2.006 2.006]; % <-- Isotropic g-tensor
% Sys.Nucs = '14N'; % <-- Removed hyperfines
% Sys.A = [11 11 95]; % MHz
Sys.lwpp = 5; % MHz
% Simulate frequency-sweep spectrum to set pulse excitation bands
pepper(Sys,Exp);
%%
% Define basic experiment parameters
Exp.mwFreq = 9.05; % GHz <-- Modifying this changes the frequency of the calculate trace
% Exp.Field = 714.4773505*Exp.mwFreq/Sys.g(2)/10; % mT <-- Uncommenting this gives totally flat patterns
% Define pulses
p90.Type = 'quartersin/linear';
p90.tp = 0.200; % pulse length, µs
p90.Flip = pi/2; % flip angle, radians
p90.Frequency = [-120 120]; % excitation band, MHz
p90.trise = 0.030; % rise time, µs
p180 = p90;
p180.tp = 0.100; % µs
p180.Flip = pi; % rad
% Define pulse sequence
tau = 0.2; % µs
Exp.Sequence = {p90 tau p180 tau+p180.tp};
% Define detection
Exp.DetWindow = [-0.15 0.15]; % µs
Exp.DetPhase = pi; % rad, for proper phasing of the signal
% Use grid resolution sufficient to get converged echo tails
Opt.GridSize = 30;
Opt.Verbosity = true;
saffron(Sys,Exp,Opt);