What is the Difference Between Fraunhofer and Fresnel Diffraction?
🆚 Go to Comparative Table 🆚The main difference between Fraunhofer and Fresnel diffraction lies in the distance between the diffracting object and the observation point, as well as the geometry of the diffracting object and the wavefront. Here are the key differences:
- Distance: Fraunhofer diffraction occurs when the observation point is located in the far-field region, relatively far away from the aperture or object. In contrast, Fresnel diffraction occurs when the observation point is closer to the aperture or object, resulting in a more complex diffraction pattern that depends on the distance between the object and the observation point.
- Geometry: Fraunhofer diffraction is characterized by a plane wavefront undergoing diffraction, while Fresnel diffraction involves a spherical or cylindrical wavefront undergoing diffraction.
- Wavefront: In Fraunhofer diffraction, the lightwave is from a source at infinity, and the rays of light passing through the slit are parallel. In Fresnel diffraction, the lightwave is from a source at a finite distance, and the rays of light passing through the slit are not parallel.
- Diffracting Object or Aperture Size: Fresnel diffraction requires a large diffracting object or aperture, while Fraunhofer diffraction can have a smaller diffracting object or aperture.
- Complexity: Fresnel diffraction patterns change as they propagate further downstream of the scattering source, whereas the shape and intensity of Fraunhofer diffraction patterns remain constant.
- Mathematical Analysis: Fraunhofer diffraction allows for a simpler mathematical analysis of the diffraction pattern, while Fresnel diffraction involves a more complex analysis that depends on the distance between the object and the observation point.
Fresnel diffraction is used in various optical devices, such as Fresnel lenses, diffraction gratings, and holographic lenses. Fraunhofer diffraction is typically observed and analyzed in the far-field region, and it is easier to observe and analyze than Fresnel diffraction.
Comparative Table: Fraunhofer vs Fresnel Diffraction
The main differences between Fraunhofer and Fresnel diffraction are the distance between the light source and the diffracting object, the type of wavefront undergoing diffraction, and the ease of observing and analyzing the diffraction pattern. Here is a table summarizing these differences:
| Fraunhofer Diffraction | Fresnel Diffraction |
|---|---|
| Spherical or cylindrical wavefront undergoes diffraction | Plane wavefront undergoes diffraction |
| Lightwave is from a source at a finite distance | Lightwave is from a source at infinity |
| Difficult to observe and analyze | Easy to observe and analyze |
| Lenses are not used | Convex lenses are used |
In Fraunhofer diffraction, the diffracting object is placed far from the screen, allowing for a simpler mathematical analysis of the diffraction pattern. In contrast, Fresnel diffraction involves placing the diffracting object closer to the screen, resulting in a more complex diffraction pattern that depends on the distance between the object and the screen.
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