From 00fb8d01e53be66fe4dfde3beee3c98acc18f3b7 Mon Sep 17 00:00:00 2001 From: Blaise Thompson Date: Sat, 14 Apr 2018 12:59:30 -0500 Subject: 2018-04-14 12:59 --- active_correction/chapter.tex | 70 ++++++++++++++++++++++++++++++------------- 1 file changed, 50 insertions(+), 20 deletions(-) (limited to 'active_correction/chapter.tex') diff --git a/active_correction/chapter.tex b/active_correction/chapter.tex index 4f7003d..7ecbe2f 100644 --- a/active_correction/chapter.tex +++ b/active_correction/chapter.tex @@ -19,13 +19,13 @@ MR-CMDS is subject to a number of possible artifacts, many of them stemming from nature of the frequency-tunable light sources we currently have. % It is self-evidently desirable to correct these artifacts, when possible. % Indeed many of these artifacts, such as OPA power, phase mismatch and absorption effects have -regularly been corrected for. % TODO: link to examples in applications section +regularly been corrected for. % TODO: link to examples in applications section, cite These corrections are applied after measurement, typically including information from other sources (such as absorption spectra, in the case of absorption effect corrections). A more interesting class of corrections are ``active'' corrections---that is, corrections that must be actively applied during acquisition and cannot be applied in post processing. % -These corrections are more insidious, and they are often neglected because the hardware and/or +These corrections are more insidious, as they are often neglected because the hardware and/or software does not allow for them. % In this chapter I explore some of these active correction strategies that are useful in the context @@ -34,17 +34,19 @@ Some of these strategies have already been implemented, others are partially imp others are still just ideas. % I hope to show that active correction is a particularly useful strategy in MR-CMDS. % -[SPECTRAL DELAY PARAGRAPH] +Section ... addresses spectral delay correction, where automated delay stages are used to +explicitly correct for small changes in optical path length at different pulse frequencies. % -[POYNTING CORRECTION PARAGRAPH] +Section ... addresses poynting correction, where mirrors with motorized pitch and yaw control are +used to actively correct for small changes in OPA output poynting. % -[EXCITATION POWER CORRECTION PARAGRAPH] +Section ... addresses (dual) chopping, used to actively subtract artifacts such as scatter and +unwanted nonlinear outputs. % +Chopping can only account for intensity level (additive) artifacts. % +Fibrillation is the opposite of chopping, as it can only account for amplitude level +\emph{iterference} effects. % +Section ... addresses fibrillation. % -[CHOPPING PARAGRAPH] - -[FIBRILLATION] - -\clearpage \section{Spectral delay correction} % ============================================================ As a frequency domain technique, MR-CMDS requires automated tuning of multiple OPAs. % @@ -53,13 +55,14 @@ Crucially, the relative arrival time of each pulse must be carefully controlled the MR-CMDS experiment. % Unfortunately, changing the output frequency also changes the optical path length, meaning that there is some unavoidable coupling between delay and frequency axes. % -Because we have full control over delay through delay stages, we can correct for this phenomenon by -choosing a different zero delay \emph{offset} for each OPA output color. % +Because we have full control over delay with our automated stages, we can correct for this +phenomenon by choosing a different zero delay \emph{offset} for each OPA output color. % This strategy has been dubbed ``spectral delay correction''. % -Spectral delay correction (SDC) is certainly the longest running active correction strategy employed +Spectral delay correction (SDC) is certainly the oldest active correction strategy employed within the Wright Group. % -SDC was first implemented by Schuyler Kain within his COLORS acquisition software. [CITE] % +SDC was first implemented by Schuyler Kain within his COLORS acquisition software. +\cite{KainSchuyler2017a} % COLORS' implementation was hardcoded for one particular OPA / delay configuration---it wasn't until PyCMDS that fully arbitrary SDC became possible through the autonomic system (see section ...). % Erin Boyle ``backported'' similar functionality into to ps\_control, although her implementation @@ -74,7 +77,13 @@ A special method of \python{Data}, \python{Data.offset} is designed to do the ne interpolation for \emph{post hoc} SDC. % In many experiments spectral delay must be actively corrected for. % -Fully coherent experiments do +Fully coherent experiments are typically performed by scanning OPA frequencies while attempting to +keep delays constant. % +In such experiments, the dataset does not in-and-of-itself contain the information needed to +offset in post processing. % +Indeed it can easily become time-prohibitive to collect the full response. % +For a three-beam experiment, an entire two dimensional delay-delay collection would be required at +each pixel to allow for post-correction. % It has been found that SDC is necessary for each individual scanned OPA, and for each separate path when pulses from a single OPA are split. % @@ -82,7 +91,7 @@ The difference between different paths is typically small, but enough to move pu amount relative to each-other. % For this reason, SDC for split OPAs is a multidimensional problem, which in principle requires a multi-dimensional acquisition to fully record. % -In practice, however, these corrections are recorded iteravely. % +In practice, however, these corrections are typically recorded iteratively. % White light sources are also interesting to consider in the context of spectral delay correction. % @@ -101,7 +110,28 @@ using a delay stage. % COLORS' has taken this idea to it's logical conclusion, with support for ``OPAs'' that are actually controlled by delay stages, although the idea has not yet been realized in practice. % -[DESCRIPTION OF FIGURE] +\autoref{act:fig:sdc} contains two plots that were automatically generated by PyCMDS in the context +of an experiment. % +In this case, the user used a sapphire plate as a nonresonant medium to record the spectral delay +dependence. % +It was a three beam $\omega_1$, $\omega_2$, $\omega_{2^\prime}$ experiment, so three corrections +were necessary: D2 vs OPA1, D1 vs OPA2, and D2 vs OPA2. % +Here we focus only on D2 ($\tau_{21}$) vs OPA1, the simplest of the corrections. % + +In the left-hand subplot of \autoref{act:fig:sdc} we see the original experiment. % +Without corrections applied, the user scanned OPA1 vs D2. % +The curvature in the plot is due entirely to SDC, as sapphire is entirely nonresonant (driven). % +Using WrightTools, PyCMDS fits each slice to find the delay that gives maximum signal. % +It then passes those separate fits through a spline to guess the ultimate SDC dependence. % +PyCMDS makes a best guess in regions where there is not enough signal to determine the appropriate +delay, like in at 800 nm in the left hand plot. % +The magnitude of the corrections are roughly 30 fs in this particular experiment: not large, but +enough to change signal levels by roughly a factor of 2. % +In other cases SDC is as much as 200 fs. % + +In the right-hand subplot the user has taken the same scan again, this time after corrections were +applied. % +The delay traces (horizontal) peaks at the same value for every OPA1 position (vertical). % \begin{figure} \includegraphics[width=0.45\textwidth]{"active_correction/sdc_before"} @@ -109,6 +139,7 @@ controlled by delay stages, although the idea has not yet been realized in pract \caption[CAPTION TODO]{ CAPTION TODO: SPECTRAL DELAY CORRECTION FIGURE } + \label{act:fig:sdc} \end{figure} \section{Poynting correction} % ================================================================== @@ -130,9 +161,6 @@ controlled by delay stages, although the idea has not yet been realized in pract } \end{figure} -\section{Excitation power correction} % ========================================================== - -\clearpage \section{Chopping} % ============================================================================= \subsection{Scatter} % --------------------------------------------------------------------------- @@ -374,3 +402,5 @@ This is a well known strategy for removing unwanted interference terms \cite{Spe McClainBrianL2004a}. % \section{Conclusions} % ========================================================================== + +In the future I'd like to do excitation power correction. % \ No newline at end of file -- cgit v1.2.3