... | ... | @@ -17,11 +17,11 @@ $`n_1-n_2=C(\sigma_1-\sigma_2)`$ |
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where $`\sigma_i`$ is an eigenvalue of the local stress tensor, $`n_i`$ is the refractive index for polarized light in the corresponding direction, and $`C`$ is called the stress-optical coefficient. The relative phase shift of wave components in the eigen-directions of local stress tensor can be calculated using:
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$`\alpha=\frac{2\piCd}{\lambda}(\sigma_1-\sigma_2)`$
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$`\alpha=\frac{2\pi C d}{\lambda}(\sigma_1-\sigma_2)`$
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where $`\lambda`$ is the wavelength of the light and $`d`$ is the distance traveled inside the material, which corresponds with the sample stiffness. Given this phase shift, the intensity of the emergent wave is:
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$`I=I_0 sin^2(\frac{\alpha}{2})=sin^2(\frac{\piCd}{\lambda}(\sigma_1-\sigma_2)) `$
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$`I=I_0 sin^2(\frac{\alpha}{2})=sin^2(\frac{\pi C d}{\lambda}(\sigma_1-\sigma_2)) `$
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This equation relates internal stress and intensity for a single wavelength. In the experiment, both the light and camera channels cover a wide range of wavelengths.
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