Compute field-modulated EPR spectrum.
yMod = fieldmod(x,y,ppAmpl) yMod = fieldmod(x,y,ppAmpl,Harmonic) fieldmod(...)
fieldmod computes the effect of modulating the field on the EPR
spectrum. Modulation of the external static field is standard in CW
EPR spectroscopy. Because of modulation, the recorded signal is approximately
the first derivative of the spectral shape and not the
absorption spectrum itself. Given an absorption spectrum y over a field
range x (in mT), fieldmod returns the modulated
absorption spectrum in yMod.
The parameter ppAmpl specifies the peak-to-peak modulation
amplitude in mT, as it is usually specified when measuring EPR
spectra. Harmonic allows for the selection of the detection
harmonic of the modulated spectrum. 1 gives the first derivative and
is the default value, higher values give higher derivatives.
The funtion returns a pseudo-modulated spectrum in the sense that it only takes into account the effect of the modulation amplitude, completely neglecting possible effects of the modulation frequency on the spectrum, like sidebands for narrow lines.
If no output variable is given, fieldmod plots the original
and the modulated spectrum.
Suppose spec is an absorption spectrum over a field range B.
Then the effect of first-harmonic detection with a field modulation amplitude of 50
Gauss (peak-to-peak) is
B = linspace(340,360,500);
spec = gaussian(B,350,1);
ppModAmplitude = 5; % units are mT !
specMod = fieldmod(B,spec,ppModAmplitude);
plot(B,specMod);
xlabel('magnetic field [mT]');
The modulation amplitude is much bigger than the line width, and the effect of overmodulation is clearly visible.
The function implements a procedure described in
garlic, gaussian, lorentzian, lshape, pepper