From 102e605b714e61cffe639fa59e0a69458bc0daca Mon Sep 17 00:00:00 2001
From: Blaise Thompson <blaise@untzag.com>
Date: Mon, 9 Apr 2018 14:01:34 -0500
Subject: 2018-04-09 14:01

---
 active_correction/chapter.tex | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/active_correction/chapter.tex b/active_correction/chapter.tex
index 6e773ec..f4447d0 100644
--- a/active_correction/chapter.tex
+++ b/active_correction/chapter.tex
@@ -44,8 +44,50 @@ I hope to show that active correction is a particularly useful strategy in MR-CM
 
 [FIBRILLATION]
 
+\clearpage
 \section{Spectral delay correction}  % ============================================================
 
+As a frequency domain technique, MR-CMDS requires automated tuning of multiple OPAs.  %
+These OPAs generate pulses, which are then manipulated and directed into a sample of interest.  %
+Crucially, the relative arrival time of each pulse must be carefully controlled in the context of
+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.  %
+This strategy has been dubbed ``spectral delay correction''.  %
+
+Spectral delay correction (SDC) is certainly the longest running active correction strategy employed
+within the Wright Group.  %
+SDC was first implemented by Schuyler Kain within his COLORS acquisition software. [CITE]  %
+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
+allowed only for a simple, first order linear correction.  %
+
+Sometimes, spectral delay can be corrected for after-the-fact.  %
+Post processed spectral delay correction can only be done if all relevant delays are scanned during
+the experiment.  %
+A common example is transient absorption, where the single delay axis is typically scanned at each
+color coordinate.  %
+A special method of \python{Data}, \python{Data.offset} is designed to do the necessary
+interpolation for \emph{post hoc} SDC.  %
+
+In many experiments spectral delay must be actively corrected for.  %
+Fully coherent experiments do 
+
+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.  %
+The difference between different paths is typically small, but enough to move pulses a noticeable
+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.  %
+
+[ALTHOUGH ACTIVE, CAN SOMETIMES BE CORRECTED FOR IN POST: SEE WRIGHTTOOLS.OFFSET]
+
+[SDC IN CONTEXT OF WHITE LIGHT]
+
 \begin{figure}
 	\includegraphics[width=0.45\textwidth]{"active_correction/sdc_before"}
  	\includegraphics[width=0.45\textwidth]{"active_correction/sdc_after"}
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