- Lorentz absorption being subject to x-axis modulation
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The modulation causes disortion of the Lorentz profile (as well as any other profile, too). To obtain the effective line width of such distorted profile, the time dependent signal profile (see figure above) must be calculated and Fourier-transformed. The first harmonic (at the modulation frequency) as a function of the x-axis gives the effective 1st-derivative signal profile measured in the experiment. The line broadening (here "peak-to-peak") as a function of the modulation intensity is shown below (rough calculation).