Zonal plate

Binary zone plate.

Fresnel Area Plate - a device used to focus light, unlike a lens, uses diffraction instead of refraction.

It consists of translucent light and dark areas that correspond to the next Fresnel zones.

Fresnel-confused. Plate design

The radius of the circles separating the other zones is r n = n & # x03BB; f + n 2 & # x03BB; 2 4 {\displaystyle r_{n}={\sqrt {n\lambda f+{\frac {n^{2}\lambda ^{2}}{4}}}}}

where n is a natural number, λ is the wavelength, and f is the focal length. If the area plate radius is much smaller than the focal length, the pattern can be approximated by r n & # x2243; n f & # x03BB; {\displaystyle r_{n}\simeq {\sqrt {nf\lambda }}}

From the above pattern, the surface of all rings (both light and dark) is the same. Principle of operation

Waveforms with different amplitudes and phases are interfering with the picture, interfering with each other. One way to reinforce the intensity in the focus is to cut out those contributors that lead to destructive interference (canceling each other's amplitudes). This is usually done by blackening these places on the plate, which give a phase opposite to the wave phase passing through the center of the plate.

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