Dear Sir,

in principle, your question was already answered by J.B.

The Voigt profile represents a convolution of the Lorenzian-like

signal from the sample and the Gaussian-like response function

from the experimental probe (i.e. spectrometer in your case.)

Just let me give an additional remark to the Lorenzian part:

Why is the sample´s signal Lorenzian-like? Just remember an

experiment from your very first lecture in mechanics, namely

Pohl´s wheel (i.e. a rotation pendulum.)

Changing the frequency of the excitation via a piston rod will change

the amplitude of the rotating motion of the wheel with the amplitude being

largest when w is close to the eigenfrequency w0 of the wheel

(exact value depends on damping).

Solving the inhomogeneous differential equation of this system gives

a Lorenzian shape of the w dependence for the power that is needed

to do this excitation per period.

When applying absorption spectroscopy, you do the same.

The closer you get to a particular excitation threshold of the samples

material the larger is the power you extract from your exciting

light beam (the measured intensity is just power per area)

In other words: Pohl´s Wheel stands for your sample, the mechanical

excitation via the piston rod stands for your light beam.

Sincerely, FM

Thank you Mr. J. B. and Mr. Frank.

Another way to think about the Lorentzian part is, the spectrum is the fourier transform of the field autocorrelation function (see Wiener-Khinchin). Lifetime broadening e.g. from collisions and radiative decay yields a decaying exponential autocorrelation function, and the Fourier transform of an exponential is a Lorentzian.