2018-04-15 21:35

1 files changed, 104 insertions, 35 deletions

diff --git a/opa/chapter.tex b/opa/chapter.tex
index 3d163e2..db88304 100644
--- a/opa/chapter.tex
+++ b/opa/chapter.tex
@@ -16,7 +16,8 @@
 \section{Introduction}  % =========================================================================

 

 In frequency-domain Multi-Resonant Coherent Multidimensional Spectroscopy (MR-CMDS), automated

-Optical Parametric Amplifiers (OPAs) are used to actively scan excitation color axes. [CITE]  %

+Optical Parametric Amplifiers (OPAs) are used to actively scan excitation color axes.

+\cite{CerulloGiulio2003a}  %

 To accomplish these experiments, exquisite OPA performance is required.  %

 During the experiment, motors inside the OPA move to pre-recorded positions to optimize output at

 the desired color.  %

@@ -84,6 +85,8 @@ propagated to all downstream stages.  %
 

 % BJT: consider putting an example curve figure

 

+% TODO: table of curve methods and attributes

+

 \section{TOPAS-C}  % ==============================================================================

 

 The TOPAS-C is a popular commercially available motorized OPA.  %

@@ -94,12 +97,40 @@ frequencies.  %
 It ranges from the mid infrared (accessible through difference frequency generation) to the

 ultraviolet (accessible through multiple second harmonic upconversion).  %

 

-% TODO: introduction to the internal design of the OPA

+\autoref{opa:fig:TOPAS-C} diagrams the internals of the TOPAS-C initial stage, where signal and

+idler are generated.  %

+Upon entering the OPA, roughly 98\% of pump light is split off immediately (BS1).  %

+The remaining 2\% goes on to be split again (BS2).  %

+After being attenuated further and passed through an aperture, part of this 800 nm light is sent

+into a sapphire plate to generate white light.  %

+This white light is then intentionally chirped, and mixed with the other small portion of the pump

+\python{non-collinearly} in NC1.  %

+The angle of the crystal is tuned, as is the relative arrival time of chirped white light and the

+small pump portion.  %

+These two degrees of freedom control the efficiency of conversion at a given color in C1, and

+together they make up the ``preamp''.

+I describe my strategy for preamp tuning in \autoref{opa:sec:preamp}.  %

+

+The signal portion from the preamp is picked off and meets the gigantic 98\% portion of pump split

+off at the very beginning in NC2.  %

+Again, the relative arrival time and crystal angle are motorized internally.  %

+Together these degrees of freedom make up the ``poweramp''.

+I describe my strategy for poweramp tuning in \autoref{opa:sec:poweramp}.  %

+

+After the poweramp, the output signal and idler can be sent through appropriate filters and,

+optionally, mixed further in three subsequent mixing stages to create all of the ranges seen in

+\autoref{opa:fig:ranges}.  %

+Each of these mixing stages has only crystal angle tunability.  %

+I describe my strategy for mixer tuning in \autoref{opa:sec:mixer}.  %

+

+It is important to realize that the total conversion efficiency for each output color varies wildly

+over all of the different mixing strategies.  %

+\autoref{opa:fig:powers} shows the empirical-best output energy achievable for each setpoint.  %

 

 \begin{figure}

   \includegraphics[width=\textwidth]{opa/OPA_ranges}

   \caption{

-    CAPTION TODO

+    TOPAS-C interaction ranges.

   }

   \label{opa:fig:ranges}

 \end{figure}

@@ -108,38 +139,52 @@ ultraviolet (accessible through multiple second harmonic upconversion).  %
   \includegraphics[width=\textwidth]{opa/TOPAS-C}

   \caption[TOPAS-C internal optics and beam path.]{

     TOPAS-C internal optics and beam path.  %

-    Image taken from manual, originally generated by Light Conversion [CITE].  %

+    Image taken from manual, originally generated by Light Conversion.  %

   }

   \label{opa:fig:TOPAS-C}

 \end{figure}

 

 \begin{figure}

   \includegraphics[width=\textwidth]{opa/OPA_powers}

-  \caption{

-    CAPTION TODO

+  \caption[TOPAS-C interaction range output powers.]{

+    TOPAS-C interaction range output powers.

   }

-  \label{opa:fig:preamp}

+  \label{opa:fig:powers}

 \end{figure}

 

-\section{Preamp}  % ===============================================================================

+\section{Preamp} \label{opa:sec:preamp}  % ========================================================

 

 In TOPAS-C OPAs, a small portion of input light is used to generate a signal seed in a BBO crystal

 ``C1''.  %

 A motorized delay stage ``D1'' is used to temporally overlap a particular color in chirped white

 light with 800 nm pump.  %

 C1 angle is tuned to optimize phase matching.  %

-Measured seed intensity and color for all combinations of C1 and D1 position are shown in

-\autoref{fig:preamp}.  %

 

-Output color and intensity are not separable along the preamp motor axes.  %

-We therefore use a multidimensional fitting strategy to find the best preamp motor positions, as

-shown below.  %

-

-% TODO: procedure

+Measured seed intensity and color for all combinations of C1 and D1 position are shown in

+\autoref{opa:fig:preamp}.  %

+Crucially, output color and intensity are not separable along the preamp motor axes.  %

+We are obligated to use a multidimensional fitting strategy to find the best preamp motor positions

+at each setpoint.  %

+

+Luckily we have an InGaAs near-infrared array detector, so it is very quick to capture the entire

+output spectrum at each motor position.  %

+PyCMDS visits an entire series of (C1, D1) positions, scanning D1 about the prior best position for

+each C1 in the curve.  %

+

+\autoref{opa:fig:preamp_flowchart} diagrams the preamp processing procedure in its entirety.  %

+The original datset is three-dimensional in C1, D1, color.  %

+In the first step, the dimensionality is reduced by fitting each array slice to extract a center,

+amplitude and width.  %

+These fits are interpolated to find contours of constant output color.  %

+I then search along that contour in \emph{intensity} space to find the motor positions that give

+maximum intensity for that color.  %

+Finally I fit a smooth spline through those chosen values to generate the output curve.  %

 

 A representative preamp tune procedure output image is shown in \autoref{fig:autotune_preamp}.  %

+This is an automatically generated image from PyCMDS.  %

 The thick black line is the final output curve.  %

 The dark grey lines are the contours of constant color.  %

+Each contour of constant color is marked with the output color in nanometers.  %

 The colorbar shows the Delaunay-interpolated intensity values for each motor position.  %

 

 Preamp tuning takes less than 20 minutes, in large part due to a NIR array detector which collects

@@ -148,7 +193,7 @@ the full spectrum at each motor position.  %
 \begin{figure}

   \includegraphics[width=\textwidth]{opa/preamp}

   \caption{

-    CAPTION TODO

+    TOPAS-C preamp motortune.

   }

   \label{opa:fig:preamp}

 \end{figure}

@@ -156,26 +201,27 @@ the full spectrum at each motor position.  %
 \begin{figure}

   \includegraphics[width=\linewidth]{opa/preamp_flowchart}

   \caption{

-    CAPTION TODO

+    Preamp tune procedure flowchart.

   }

+  \label{opa:fig:preamp_flowchart}

 \end{figure}

 

 \begin{figure}

   \includegraphics[width=\linewidth]{opa/autotune_preamp}

   \caption{

-    CAPTION TODO

+    Preamp tuning output.

   }

   \label{opa:fig:autotune_preamp}

 \end{figure}

 

-\section{Poweramp}  % =============================================================================

+\section{Poweramp} \label{opa:sec:poweramp}  % ====================================================

 

 Once generated, the seed goes on to be amplified in a second BBO crystal ``C2'' with the rest of

 the 800 nm pump.  %

 Optimizing this amplification step is primarily a matter of setting C2 angle.  %

 A small delay correction ``D2'' is necessary to account for dispersion in the seed optics.  %

 To fully explore poweramp behavior, we need to tak a C2-D23 scan for each seed color.  %

-Measured output intensity and color in this 3D space is represented in \autoref{fig:poweramp}.  %

+Measured output intensity and color in this 3D space is represented in \autoref{opa:fig:poweramp}.  %

 Note that the motor axes are scans about the previously recorded tuning curve value.  %

 

 The best position (zero displacement along both axes) is chosen to maximize output intensity while

@@ -187,8 +233,7 @@ dimensions (this is especially true at the edge output colors).  %
 In the poweramp, the increased dimensionaity makes it too expensive to do a full multidimensional

 tuning procedure.  %

 Instead we emply an iterative procedure as diagrammed below.  %

-

-% TODO: procedure

+\autoref{fig:opa:poweramp_flowchart} diagrams this iterative procedure.  %

 

 We always end the iteration(s) with C2 so that the OPA's color calibration is as good as

 possible.  %

@@ -209,7 +254,7 @@ curve (colored X's).  %
 \begin{figure}

   \includegraphics[width=\linewidth]{opa/poweramp}

   \caption{

-    CAPTION TODO

+    TOPAS-C poweramp motortune.

   }

   \label{opa:fig:poweramp}

 \end{figure}

@@ -217,14 +262,15 @@ curve (colored X's).  %
 \begin{figure}

   \includegraphics[width=\linewidth]{opa/poweramp_flowchart}

   \caption{

-    CAPTION TODO

+    Poweramp tune procedure flowchart.

   }

+  \label{opa:fig:poweramp_flowchart}

 \end{figure}

 

 \begin{figure}

   \includegraphics[width=\textwidth]{opa/d2}

   \caption{

-    CAPTION TODO

+    Poweramp D2 tuning output.

   }

   \label{opa:fig:d2}

 \end{figure}

@@ -232,24 +278,47 @@ curve (colored X's).  %
 \begin{figure}

   \includegraphics[width=\textwidth]{opa/c2}

   \caption{

-    CAPTION TODO

+    Poweramp C2 tuning output.

   }

   \label{opa:fig:c2}

 \end{figure}

 

-\section{Mixers}  % ===============================================================================

+\section{Mixers} \label{opa:sec:mixers}  % ========================================================

+

+Because mixers only have one degree of freedom each (crystal angle), there is really not that much

+ambiguity about what the ideal motor positions are.  %

+In fact, the best motor positions can be chosen simply by taking excursions relative to the old

+points (as in \autoref{opa:fig:d2}) and picking the points with the highest intensity.  %

+After choosing motor positions, a simple correction for actual output frequencies can be applied

+using the monochromator.  %

 

-[DESCRIPTION OF MIXERS]

+I have prepared two functions: \python{process_intensity} and \python{process_tune} which

+accomplish each of these goals.  %

+They are general, capable of being used for \emph{any} mixer or tune test.  %

+

+PyCMDS can also explicitly take a spectrum at each motor position.  %

+This information takes longer to collect, but less human intervention---so it is a valid strategy

+that is sometimes employed.  %

 

 \section{Generalizability}  % =====================================================================

 

+This chapter has considered the automated procedures used in tuning the TOPAS-C, just one of the

+four models of OPA owned by the Wright Group.  %

+Simply put, this is because the other three OPA models (all picosecond OPAs) are easy to tune.  %

+

+\autoref{opa:fig:ps_opa} displays the entire tuning space for generation of signal and idler in one

+of the picosecond OPAs.  %

+In contrast to the TOPAS behavior, where neither motor axis constrains the output very well,

+\emph{both} motors have very narrow features in this picosecond OPA.  %

+This means that it is at all times \emph{unambiguous} whether a given motor position is ideal.  %

+

+Much like the mixers, these OPAs can be readily tuned using a combination of the general functions

+\python{process_intensity} and \python{process_tune}.  %

+

 \begin{figure}

   \includegraphics[width=\textwidth]{"opa/signal_and_idler_motortune"}

-  \caption[CAPTION TODO]{

-    CAPTION TODO

+  \caption[Picosecond OPA motortune.]{

+    Motortune for picosecond OPA, monitored using a single pyroelectric detector.

   }

-\end{figure}

-

-\section{Future directions}  % ====================================================================

-

-% TODO: discuss Attune
\ No newline at end of file
+  \label{opa:fig:ps_opa}

+\end{figure}
\ No newline at end of file