\section{Chopper\_simple: An ideal chopper}
\index{Optics!lens}
\mcdoccomp{optics/Chopper_simple.parms}
\texttt{Chopper\_simple} is an idelized version of a chopper with a rectangular chopper opening which may open
instantly and has no side-scattering etc.

It models the chopper with a blocking infinitely thin aperture which becomes transparent
in the time interval $t\in\left[\mathit{t0},\mathit{t0}+\tau\right]$.
This is an idelized version of a chopper where the chopper opening is rectangular which may open
instantly (if \textit{t\_rise}$=0$, the default). For nonzero rise time the aperture simply becomes gradually less opaque
for $t\in\left[\mathit{t0}-\textit{t\_rise},\mathit{t0}\right]$.

For correct normalization of intesity a chopper period, \textit{T}, must also be set.

\textit{is\_first} is useful when using \textbf{Chopper\_simple} with continous sources who inherently have no time-dependence. Thus the emission time of the photon
ray is arbitrary, and the chopper defines the temporal signature of the beam,
i.e. it simply sets the time-parameter of the photon ray randomly in the
opening window of the chopper. Naturally this should only be used for the \emph{first} chopper
element in a simulation.
