\section{Lens\_parab: Thick parabolic CRL}
\label{s:lens-parab}
\index{Optics!lens}
\mcdoccomp{optics/Lens_parab.parms}

Component model of a stack of compund refractive lenses. Each lens in the stack
is modelled by two $2D$ parabolic surfaces, and rays are traced through all the
complete stack taking the displacement of the surfaces into account. This is
naturally less efficient than a thin lens approximation.

The logic behind the model is the following: a photon interacts with the
surface of the lens at a certain angle $\Theta$, which alters in accordance
with Snell's law upon photon's entering the lens's material. The combination of
the refractive process inside material (that is characterized by a material
datafile) and the interaction with a geometrical surface results in a photon's
new trajectory, i.e. in focusing.

The functionality of \texttt{Lens\_parab\_Cyl}, \texttt{Lens\_parab\_rough},
and \texttt{Lens\_parab\_Cyl\_rough} will be merged into this component.
