Physics · Ch 6 — Optics
Fresnel and Fraunhofer Diffractions
6.11.1
Fresnel and Fraunhofer Diffractions
Based on the shape of the wavefront undergoing diffraction, diffraction is classified into two types. Fresnel diffraction involves a spherical or cylindrical wavefront, arising when the light source is at a finite distance; it does not require convex lenses to observe under laboratory conditions, but is comparatively difficult to observe and analyse mathematically. Fraunhofer diffraction involves a plane wavefront, arising when the source is effectively at infinity; it does require convex lenses in the laboratory (to collimate the source and to focus the diffracted pattern), but is comparatively easy both to observe and to analyse -- which is …
Table 6.4Difference between Fresnel and Fraunhofer diffractions
| S.No. | Fresnel diffraction | Fraunhofer diffraction |
|---|---|---|
| 1 | Spherical or cylindrical wavefront undergoes diffraction | Plane wavefront undergoes diffraction |
| 2 | Light wave is from a source at finite distance | Light wave is from a source at infinity |
| 3 | For laboratory conditions, convex lenses need not be used | In laboratory conditions, convex lenses are to be used |