% TODO: Rapid and economical data acquisition in ultrafast frequency-resolved spectroscopy using
% choppers and a microcontroller https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-16-18126

\chapter{Hardware}  % -----------------------------------------------------------------------------

In this chapter I collect some of the specific hardware contribution details that do not belong in
the body of the dissertation.  %

\section{Adjustable periscopes}  % ----------------------------------------------------------------

OPAs output horizontal or vertical polarizations according to which tuning process is used.  %
Our experiments are opinionated about polarization, so some strategy for aligning polarization is
necessary.  % TODO: cite opinionated about polarization
In addition, it is useful to bring all excitation beams to the same height.  %
To this end, I designed and constructed two adjustable periscopes.  %
Each periscope is designed to bring OPA output to table height standard (5 inches) while either
keeping or switching polarization.  %
Both polarization configurations take the same path length, so source polarization can be switched
without large changes to zero delay.  %
All of this is done with just two (switched polarization) or three (kept polarzation)
reflections.  %
A picture of these periscopes is shown in \ref{f:periscope}.  %

\begin{figure}[htp!]
	\centering
	\includegraphics[width=\textwidth]{"hardware/periscope"}
	\label{f:periscope}
	\caption{CAPTION TODO}
\end{figure}

While these periscopes are easy to align, their unique design means that it is not necessarily
obvious what the correct strategy is.  %
The following strategy will always converge:
\begin{enumerate}
  \item use two ``magic'' apertures along the output beamline
  \item in flipped polarization (two mirror configuration):
    \begin{itemize}
      \item use the stage (green X, Y) to align near aperture
      \item use the upper mirror (yellow TA, TB) to align far aperture
      \item iterate above
    \end{itemize}
  \item in kept polarization (three mirror configuration):
    \begin{itemize}
      \item use stage X (green X) and upper mirror height (yellow TC) to align near aperture
      \item use lower mirror (pink SA, SB) to align far aperture
      \item iterate above
    \end{itemize}
\end{enumerate}
The kept polarization alignment is derivative of the fixed polarization alignment.  %
One must ensure that the fixed polarization is correctly aligned at all times.  %
  
Mirror B (aqua) is magnetically mounted to switch between polarization conditions.  %
Ensure that the lower turning mirror (pink) does not bump into mirror B (aqua) in polarization
swtiching configuration.  %
The lower turning mirror is on a rail (pink SC).  %
This rail is a rough adjust for the same degree of freedom as pink SA.  %
Adjust the rail only to ensure that the beam is roughly centered on the free aperture of the
turning mirror.  %

The first reflection is often accomplished using a wedge, as OPA output may be strong enough to
damage downstream optics.  %
This optic can and should be replaced if more of the OPA output is desired on the table (keeping
damage thresholds in mind).  %

\subsection{Wedge polarization preference}

TODO: wedges will be more efficent at reflecting horizontal / vertical at 45 degrees

\section{Automated transmissive filters}  % -------------------------------------------------------

TODO

\section{Electronics}  % --------------------------------------------------------------------------

TODO