Fresnel number

The Fresnel number F, named after the physicist Augustin Jean Fresnel, is a dimensionless parameter, the. In optics, particularly in flexion, is used It describes how strong is the diffraction of a light beam at a panel.

For an electromagnetic wave that passes through an orifice and impinges on a screen, the Fresnel number is defined as F

With

• A is the characteristic size of the aperture (eg its radius )
• L is the distance of the screen to the aperture
• λ is the wavelength.

Depending on the value of F, one can distinguish the following cases:

• : Fraunhofer diffraction (eg, panel a very small or beam profile in the far field, ie removal of L very large)
• : Fresnel diffraction
• : Geometrical optics (eg, panel a very large or beam profile in the near field, ie removal of L very small).