Fresnel number
In optics, in particular scalar diffraction theory, the Fresnel number (F), named after the physicist Augustin-Jean Fresnel, is a dimensionless number relating to the pattern a beam of light forms on a surface when projected through an aperture. == Definition == For an electromagnetic wave passing through an aperture and hitting a screen, the Fresnel number F is defined as F = a 2 L λ , {\displaystyle F={\frac {a^{2}}{L\lambda }},} where a {\displaystyle a} is the characteristic size (e.g.