Non-Ideal Lorentzians: Quantifying Shape Deviation from Ideal

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The discussion focuses on analyzing the transmissivity of a high-Q resonator, which ideally should exhibit a Lorentzian shape. However, measurements indicate that the shape distorts with temperature changes, prompting interest in understanding this phenomenon. The user seeks a method to quantify the deviation from the ideal Lorentzian shape as a function of temperature. They recall encountering a "shape factor" in atomic spectroscopy but struggle to find relevant resources. This highlights a need for established techniques to measure and represent shape deviations in resonant systems.
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"Non ideal" Lorentzians

I am not sure if this is a question about math, physics or electrical engineering...
Anyway, I am currently trying to analyze some measurement data. What I have is essentially the transmissivity (i.e. S21 using EE terminology) for a high-Q resonator (Q value about 10^6). Ideally a resonator of this type should have a shape that is very nearly Lorentzian. However, what we see is that the shape depends on the temperature and at elevated temperatures s clearly "distorted" , we believe there is a rather interesting reason for this temperature dependence (meaning it is worth looking into).
Now, I would like to somehow "quantify" this change to that I can plot it as a function of temperature.

Is there a generally accepted way to quantify how much the shape of a resonance deviates from an ideal Lorentzian?
I seem to remember seeing something similar, i.e. a "shape factor" (not the same thing as the shape factor in EE), being used in atomic spectroscopy but I can't find anything useful using Google schoolar.
 
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