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(Pseudo) Voigt profiles

Voigt profiles are provided as pseudo-Voigt approximation, consisting of a weighted sum

\begin{displaymath}Voigt_{\rm pseudo} = (1-\eta) Gauss(\Gamma) + \eta Lorenz(\Gamma) \end{displaymath}

of a Gaussian and a Lorenzian. Here, the FWHM $\Gamma$ is computed as

\begin{displaymath}\Gamma = (\Gamma^5_{\rm G} + 2.69296 \Gamma^4_{\rm G} \Gamma_...
...7842 \Gamma_{\rm G} \Gamma^4_{\rm L} + \Gamma^5_{\rm L})^{1/5}.\end{displaymath}

The mixing parameter $\eta$ is computed as

\begin{displaymath}\eta = 1.36603 (\Gamma_{\rm L}/\Gamma) - 0.47719 (\Gamma_{\rm L}/\Gamma)^2
+ 0.11116 (\Gamma_{\rm L}/\Gamma)^3. \end{displaymath}

(For reference, see P. Thompson, D.E. Cox, J.B. Hastings, J. Appl. Cryst. 1987, 20, 79.)

To use a Voigt profile, you need to define two lines, one with a Gaussian, the other with a Lorenzian profile, and lock their wavelengths. The required parameters in the parameter file are listed in Sect. 6.3. In the GUI, use the Profile and LOCK toggles in the line definition window (note that LOCK will lock to the wavelength of the preceding line, thus you should toggle this only for the second line in your Gaussian/Lorenzian pair). The Voigt profiles are not supported in the IDL version.


next up previous contents
Next: Description of output Up: The procedure Previous: Beta profiles   Contents
Jan-Uwe Ness
2003-05-23