The far-field pattern of a diffracting screen illuminated by a point source may be observed in the image plane of the source. The far-field diffraction pattern of a source may also be observed (except for scale) in the focal plane of a well-corrected lens. When observed, the image of the aperture from Fresnel diffraction will change in terms of size and shape, namely, the edges become more or less "jagged", whereas the aperture image observed when Fraunhofer diffraction is in effect only alters in terms of size due to the more collimated or planar nature of the waves. When the distance or wavelength is increased, Fraunhofer diffraction occurs due to the waves going towards becoming planar, over the extent of diffracting apertures or objects. When a diffracted wave is observed parallel to the other at an initial near-field distance, Fresnel diffraction is seen to occur due to the distance between the aperture and the observed canvas ( σ) being more than 1 when calculated with the Fresnel number equation, which can be used to observe the extent of diffraction in the parallel waves through the calculation of the aperture or slit size ( a), wavelength (λ) and distance from the aperture, ( L). When waves pass through, the wave is split into two diffracted waves travelling at parallel angles to each other along with the continuing incoming wave, and are often used in methods of observation by placing a screen in its path in order to view the image-pattern observed. Forms Explanation Fresnel diffraction occurs when:įraunhofer diffraction goes from the idea of a wave being split into several outgoing waves when passed through an aperture, slit or hole, and is usually described through the use of observational experiments using lenses to purposefully diffract light.
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