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% http://scifun.chem.wisc.edu/Thesis_Awards/chapter_guidelines.html
\chapter{Public}
\section{Chemical systems} % ---------------------------------------------------------------------
Chemical systems are complex! %
They contain many molecules ($10^{25}$ in a cup of coffee, 1 trillion in each human cell). %
These molecules have multiple interaction modes, both internal (intramolecular) and external
(intermolecular). %
The reactivity of the system taken as a whole can be dominated by very rare but very important
species, \textit{e.g.} catalysts. %
Despite this complexity, scientists have gotten very good at describing chemical systems through
representations of dynamic equilibrium. %
In such situations, several key parameters emerge: %
\begin{itemize}
\item concentration
\item timescale (rate)
\item lengthscale
\end{itemize}
\subsection{Concentration}
\subsection{Timescale}
% TODO: dynamics in chemical systems: collision time, dephasing, rotation, relaxation, diffusion...
\subsection{Lengthscale}
\section{Analytical chemistry} % -----------------------------------------------------------------
Traditionally, chemists have seen fit to divide themselves into four specializations: analytical,
inorganic, organic, and physical. %
In recent years, materials chemistry and chemical biology have become specializations in their own
right. %
This dissertation focuses on analytical chemistry. %
Analytical chemists separate, identify, and quantify chemical systems. %
To do this, we build instruments that exploit physical properties of the chemical components: %
\begin{itemize}
\item separation science (chromatography, electrophoresis)
\item mass spectrometry
\item electrochemistry
\item microscopy
\item spectroscopy
\end{itemize}
Spectroscopy is a family of strategies that exploit the interaction of chemical systems with
light. %
\section{Spectroscopy} % -------------------------------------------------------------------------
Molecules respond to electric fields. %
Static electric fields cause charged molecules (ions) to move, as in electrophoresis and mass
spectrometry. %
Oscillating electric fields, also known as light, can interact directly with the molecules
themselves, driving transitions. %
However, these transitions can only be driven with the appropriate frequency of light
(resonance). %
Different frequencies (colors) of light interact with different kinds of transitions, revealing
different features of the molecule of interest. %
% TODO: different energy ranges / transition types (nuclear, rotational, vibrational, electronic)
% TODO: how is a photon created or absorbed?
\subsection{Nonlinear spectroscopy}
Spectroscopy is fantastic, but sometimes simple experiments don't reveal everything. %
Nonlinear spectroscopy uses multiple electric fields simultaniously, revealing even more
information about the chemical system. %
% TODO: simple graphic of homogeneous vs inhomogeneous broadening
% TODO: 2D freq-freq with increasing inhomogeneity (from Dan's theory work)
\section{Instrumentation} % ----------------------------------------------------------------------
To accomplish nonlinear spectroscopy, specialized light sources are needed: %
\begin{itemize}
\item gigantic electric fields
\item ultrafast time resoution
\item tunable frequencies
\end{itemize}
\subsection{LASER}
These sources are made using Light Amplified by the Stimulated Emission of Radiation (LASER). %
% TODO: discussion of the original LASER, basic LASER physics
% TODO: discuss temporal coherence
% TODO: discuss pulsed sources
By keeping a wide range ofr colors in phase simulatniously, we are able to create truly ultrafast
pulses of light. %
The work presented in this dissertation was primarily taken using a 35 fs 1 KHz system. %
35 fs ($35\times10^{15}$ second) pulses are incredibly short:
\begin{equation}
\frac{\text{pulse duration (35 fs)}}{\text{time between pulses (1 ms)}} \approx
\frac{\text{5.75 months}}{\text{age of universe (13.7 billion years)}} % TODO: cite age
\end{equation}
proportionally, our sample spends 6 months in the ``sun'' for every age of the unverse in the
dark. %
Because all of the energy within the pulse is compressed to such a short period of time, these
pulses are also incredibly powerful:
\begin{equation}
\frac{\text{energy per pulse (4 mJ)}}{\text{pulse duration (35 fs)}} \approx
\frac{\text{US electricity generation} (5.43\times10^{11} W)}{5} % TODO: cite generation
\end{equation}
this laser outputs electric fields one fifth as powerful as total US electricity generation (2016).
% TODO: pulses are very thin (draw circle, use thickness of paper) to motivate 'hard to handle'
\subsection{OPA}
% https://osf.io/vwhjk/
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