FresnelDiffraction (Near-field Diffraction)
Fresnel diffraction also referred to as near-field diffraction is a form of diffraction which occurs when awave passes through an aperture and diffracts in the near field, causing anydiffraction pattern observed to differ in size and shape depending on thedistance between the sources of the obstruction (aperture) to the screen(projection).
When either the distance from the source to the obstructionor the distance from the obstruction to the screen is comparable to the size ofthe obstruction, Fresnel diffraction occurs.
Radiating Near Field or Fresnel Region. Far Field or Fraunhofer Region. The far field region is the most important, as this determines the antenna's radiation pattern. Since antennas are used to communicate wirelessly from long distances, this is the region of operation for most antennas. We will start with the Far Field. Far Field (Fraunhofer.
What You Need ToKnow About Fresnel Diffraction
Fresnel And Fraunhofer Diffraction
- If the source of light and screen are at finitedistance from the obstacle, then the diffraction is referred to as FresnelDiffraction.
- Fresnel diffraction patterns occur on flatsurfaces.
- To obtain Fresnel diffraction, zone plates areused.
- Shape and intensity of diffraction patternchange as the waves propagate downstream of the scattering source.
- Diffraction pattern move along the correspondingshift in the object.
- In Fresnel diffraction, wavefronts leaving theobstacle are also spherical.
- In Fresnel diffraction, source and screen arefar away from each other.
- In Fresnel diffraction, incident wavefronts arespherical.
- In Fresnel diffraction, the convex lens is notrequired to converge the spherical wavefronts.
- For instance, in the far field, the Fraunhofer pattern near the axis of a black disc is essentially the same as that of an opaque sphere of the same radius, and the Fresnel pattern for light passing near the boundary of a convex body with a large radius of curvature is very similar to that of an infinite half-plane 1).
- Two different regimes for diffraction are usually identified: Fresnel and Fraunhofer. Fresnel diffraction is the regime in which the diffracted waves are observed close (as compared to the size of the object causing the diffraction) to the place where they are diffracted. Fresnel diffraction is usually very complicated to work with.
- Fresnel and Fraunhofer diffraction patterns and dynamic transition between them can be easily obtained on a distance of few meters, what gives an opportunity to use our setup as a lecture experiment.
Fraunhofer Diffraction(Far-field Diffraction)
Fraunhofer diffraction also referred to as Far-field diffraction, is a form ofdiffraction in which light source and the reception screen are considered as atinfinite distances or at great distance from the diffracting object, so thatthe resultant wave fronts are considered as planar rather than spherical.
What You Need ToKnow About Fraunhofer Diffraction
Fresnel And Fraunhofer Diffraction
- If the source of light and screen are atinfinite distance from the obstacle then the diffraction is referred to asFraunhofer diffraction.
- Fraunhofer diffraction patterns occur onspherical surfaces.
- To obtain Fraunhofer diffraction, thesingle-double plane diffraction grafting is used.
- Shape and intensity of a Fraunhofer diffractionremains constant.
- Diffraction pattern remains in a fixed position.
- In Fraunhofer diffraction, diffraction obstaclegives rise to wavefronts which are also plane.
- In fraunhofer diffraction, source and the screenare far away from each other.
- In Fraunhofer diffraction, incident wavefrontson the diffracting obstacle are plane.
- In Fraunhofer diffraction, Plane diffractingwavefronts are converged by means of a convex lens to produce a diffractionpattern.
Also Read:Difference Between Interference And Diffraction Of Light
|BASIS OF COMPARISON||FRESNEL||FRAUNHOFER Diffraction|
|Description||If the source of light and screen are at finite distance from the obstacle, then the diffraction is referred to as Fresnel Diffraction.||If the source of light and screen are at infinite distance from the obstacle then the diffraction is referred to as Fraunhofer diffraction.|
|Pattern Occurrence||Patterns occur on flat surfaces.||Patterns occur on spherical surfaces.|
|Obtaining The Diffraction||To obtain Fresnel diffraction, zone plates are used.||To obtain Fraunhofer diffraction, the single-double plane diffraction grafting is used.|
|Shape & Intensity Of Diffraction||Shape and intensity of diffraction pattern change as the waves propagate downstream of the scattering source.||Shape and intensity of a Fraunhofer diffraction remains constant.|
|Pattern Direction||Diffraction pattern move along the corresponding shift in the object.||Diffraction pattern remains in a fixed position.|
|Wavefronts||Wavefronts leaving the obstacle are also spherical.||Diffraction obstacle gives rise to wavefronts which are also plane.|
|Source And Screen||Source and screen are far away from each other.||Source and the screen are far away from each other.|
|Incident Wavefronts||Incident wavefronts are spherical.||Incident wavefronts on the diffracting obstacle are plane.|
|Converging The Wavefronts||The convex lens is not required to converge the spherical wavefronts.||Plane diffracting wavefronts are converged by means of a convex lens to produce a diffraction pattern.|
Also Read:Difference Between Reflection And Refraction Of Light