What Is Fresnel Diffraction (Near-field Diffraction)?
Fresnel diffraction also referred to as near-field diffraction is a form of diffraction which occurs when a wave passes through an aperture and diffracts in the near field, causing any diffraction pattern observed to differ in size and shape depending on the distance between the sources of the obstruction (aperture) to the screen (projection).
When either the distance from the source to the obstruction or the distance from the obstruction to the screen is comparable to the size of the obstruction, Fresnel diffraction occurs.
What You Need To Know About Fresnel Diffraction
- If the source of light and screen are at finite distance from the obstacle, then the diffraction is referred to as Fresnel Diffraction.
- Fresnel diffraction patterns occur on flat surfaces.
- To obtain Fresnel diffraction, zone plates are used.
- Shape and intensity of diffraction pattern change as the waves propagate downstream of the scattering source.
- Diffraction pattern move along the corresponding shift in the object.
- In Fresnel diffraction, wavefronts leaving the obstacle are also spherical.
- In Fresnel diffraction, source and screen are far away from each other.
- In Fresnel diffraction, incident wavefronts are spherical.
- In Fresnel diffraction, the convex lens is not required to converge the spherical wavefronts.
What Is Fraunhofer Diffraction (Far-field Diffraction)?
Fraunhofer diffraction also referred to as Far-field diffraction, is a form of diffraction in which light source and the reception screen are considered as at infinite distances or at great distance from the diffracting object, so that the resultant wave fronts are considered as planar rather than spherical.
What You Need To Know About Fraunhofer Diffraction
- If the source of light and screen are at infinite distance from the obstacle then the diffraction is referred to as Fraunhofer diffraction.
- Fraunhofer diffraction patterns occur on spherical surfaces.
- To obtain Fraunhofer diffraction, the single-double plane diffraction grafting is used.
- Shape and intensity of a Fraunhofer diffraction remains constant.
- Diffraction pattern remains in a fixed position.
- In Fraunhofer diffraction, diffraction obstacle gives rise to wavefronts which are also plane.
- In fraunhofer diffraction, source and the screen are far away from each other.
- In Fraunhofer diffraction, incident wavefronts on the diffracting obstacle are plane.
- In Fraunhofer diffraction, Plane diffracting wavefronts are converged by means of a convex lens to produce a diffraction pattern.
Also Read: Difference Between Interference And Diffraction Of Light
Difference Between Fresnel And Fraunhofer Diffraction In Tabular Form
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