From 23e201c598024d8acce18e451ada57a54d5e92eb Mon Sep 17 00:00:00 2001 From: Blaise Thompson Date: Sun, 15 Apr 2018 21:35:24 -0500 Subject: 2018-04-15 21:35 --- opa/chapter.tex | 139 ++++++++++++++++++++++++++++++++++++++++++-------------- 1 file 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 -- cgit v1.2.3