diff --git a/Tex/theory.tex b/Tex/theory.tex
index eb016ca..02d9df9 100755
--- a/Tex/theory.tex
+++ b/Tex/theory.tex
@@ -1,6 +1,6 @@
 \chapter{Theory}
 
-
+\section{Coherence}
 Spherical waves as  solutions to wave equation
 \begin{equation}
 	E(\vec{r},t)=E_0(k,t) \frac{e^{i\vec{r}\vec{k}-iwt}}{R}
@@ -32,26 +32,51 @@ \chapter{Theory}
 Intensity in double slit leads to normalized degree of coherence $g_1$
 Visiblity is modulus of $g_1$.
 
+In a double slit setup (\fref{fig:doubleslit}), $E(r,t)=c_1 E_1(t)+c_2E2(t)$ with complex $c_2$ and $c_2$, $\left|c_1\right|\approx\left|c_2\right|$ describing the propagation to the screen. 
 
-\section{Coherence}
  \begin{figure}
  	\centering
  	\includegraphics[width=0.8\linewidth]{images/doubleslit.pdf}
  	\caption{Schematic of double slit: Monochromatic light goes through slits located at $R_1$ and $R_2$. The intensity at a position $r$ on the scree (in distance $d$) is the superposition of both paths.  If the slits are within the lateral coherence area of the source, the visibility of the interference pattern depends on the path length difference in comparison to the coherence time $\tau$.}
+ 	 \label{fig:doubleslit}
  \end{figure}
 
+
+\paragraph{First order coherence $g_1(t)$}
+
+Definition of $g_1$
+\begin{equation}
+	g^{(1)}(\vec{r}_1,t_1;\vec{r}_2,t_2= \frac{\left< E^*(\vec{r}_1,t_1)E^*(\vec{r}_2,t_2)E(\vec{r}_1,t_1)E(\vec{r}_2,t_2) \right>}{\left<\left | E(\vec{r}_1,t_1)\right |^2 \right> \left< \left |E(\vec{r}_2,t_2)\right |^2 \right>}	
+\end{equation}
+\begin{equation}
+V=\left|g_1\right|
+\end{equation}
+
 Int
 -along Glauber/Statistical Optics Goodman
 
 
-\paragraph{Michealson-Interferometer}
-\paragraph{First order coherence $g_1(t)$}
+
+
 \paragraph{Second order coherence $g_2(t_1,t_2)$}
+The definition of $g_1$ can be extended to the second order by
+\begin{equation*}
+	g^{(2)}(\vec{r}_1,t_1;\vec{r}_2,t_2= 
+	\frac{\left< E^*(\vec{r}_1,t_1)E^*(\vec{r}_2,t_2)E(\vec{r}_1,t_1)E(\vec{r}_2,t_2) \right>}{\left<\left | E(\vec{r}_1,t_1)\right |^2 \right> \left< \left |E(\vec{r}_2,t_2)\right |^2 \right>}	
+\end{equation*}
+For classical fields normalized correlations of intensities:
+\begin{equation}
+	g^{(2)}(\vec{r}_1,t_1;\vec{r}_2,t_2)= 
+		\frac{\left< I(\vec{r}_1,t_1)I(\vec{r}_2,t_2 \right>}{\left<I(\vec{r}_1,t_1)\right>\left<I(\vec{r}_1,t_1)\right>}	
+\end{equation}
 
+\paragraph{Van Cittert Zernicke}
 
 %-Hanbury Brown and Twist
 \section{Hanburry Brown Twiss}
-\paragraph{Second order coherence $g_2(x_1,x_2)$}
+Hanburry Brown and Twiss 
+
+
 \paragraph{Siegert Relation for Pseudo-Thermal Light}
 
 %-Single Photon Emitters/2nd Quant description
@@ -66,8 +91,9 @@ \section{Signal to Noise Considerations}
 %will use Peak/stdev bg definition
 Which factors influence SNR
 -lifetime/pulsewidth
--sampling conditions
--sample thickness
+-polarisation
+-sampling conditions / undersampling
+-sample thickness / coherence length
 -N images
 -N photons
 \label{chap:theory}