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Diffraction: Difference between revisions
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(Created page with "Notes on diffraction for holograms ==Theory== ===Rayleigh-Sommerfeld diffraction theory=== ==Approximations== ===Fresnel diffraction=== {{main | Wikipedia: Fresnel diffraction}} Fresnel diffraction can be used for intermediate distances. ===Fraunhofer diffraction=== {{main | Wikipedia: Fraunhofer diffraction}} Fraunhofer diffraction is used for far-field holograms. ==Resources== * Digital holography and wavefront sensing by Ulf Schnars, Claas Falldorf, John Watson, a...") |
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{{main | Wikipedia: Fresnel diffraction}} | {{main | Wikipedia: Fresnel diffraction}} | ||
Fresnel diffraction can be used for intermediate distances. | Fresnel diffraction can be used for intermediate distances. | ||
The Fresnel approximation is: | |||
<math display="block"> | |||
E(x,y,z) = \frac{e^{ikz}}{i \lambda z} \int \int E(x', y', 0) e^{\frac{ik}{2z} \left[ (x - x')^2 + (y - y')^2 \right]} dx' dy' | |||
</math> | |||
where | |||
* <math>k=2 \pi / \lambda</math> | |||
Expanding out terms, we get: | |||
<math display="block"> | |||
\begin{align} | |||
E(x,y,z) &= \frac{e^{ikz}}{i \lambda z} \int \int E(x', y', 0) e^{\frac{ik}{2z} \left[ (x - x')^2 + (y - y')^2 \right]} dx' dy'\\ | |||
&= \frac{e^{ikz}}{i \lambda z} \int \int E(x', y', 0) e^{\frac{i\pi}{\lambda z} \left[ x^2 - 2x x' + x'^2 + y^2 - 2yy' + y'^2 \right]} dx' dy'\\ | |||
&= \frac{e^{ikz}}{i \lambda z} e^{\frac{-i\pi}{\lambda z} \left[ x'^2+ y'^2 \right]} \int \int E(x', y', 0) e^{\frac{i\pi}{\lambda z} \left[ x^2 + y^2 \right] } e^{\frac{-i2\pi}{\lambda z} \left[ x x' + yy' \right]} dx' dy' \\ | |||
&= \frac{e^{ikz}}{i \lambda z} e^{\frac{-i\pi}{\lambda z} \left[ x'^2+ y'^2 \right]} \mathcal{F} \left\{ E(x', y', 0) e^{\frac{i\pi}{\lambda z} \left[ x^2 + y^2 \right] } \right\}_{p=\frac{x}{\lambda z}, q=\frac{y}{\lambda z}} | |||
\end{align} | |||
</math> | |||
===Fraunhofer diffraction=== | ===Fraunhofer diffraction=== | ||