reflection-photoelasticity.md

@@ -67,7 +67,7 @@ As shown in the above figure, under reflective polariscope, the circular polariz
 ```math
 E_1 = \sqrt{I_0}e^{i(kz-\omega t)}\hat{y}
 ```
-where $`I_0`=|E_1|^2$ is a constant called the background light intensity, $`k`$ is the wave number and $`\omega`$ is the frequency of the light. Suppose the principle direction for the stress tensor of the specimen point under consideration is $`\hat{m_1}`$ and $`\hat{m_2}`$ (corresponding to principle stress $`\sigma_1`$ and $`\sigma_2`$ respectively). Denote $`\phi = \alpha - \pi/4`$. Then in region (2) 
+where $`I_0=|E_1|^2`$ is a constant called the background light intensity, $`k`$ is the wave number and $`\omega`$ is the frequency of the light. Suppose the principle direction for the stress tensor of the specimen point under consideration is $`\hat{m_1}`$ and $`\hat{m_2}`$ (corresponding to principle stress $`\sigma_1`$ and $`\sigma_2`$ respectively). Denote $`\phi = \alpha - \pi/4`$. Then in region (2) 
 ```math
 E_{2} = \frac{1}{\sqrt{2}}\sqrt{I_0}e^{i(kz-\omega t)}(-i\hat{f}+\hat{s}) = \frac{1}{\sqrt{2}}\sqrt{I_0}e^{i(kz-\omega t)}e^{i\phi}(-i\hat{m_1}+\hat{m_2})
 ```