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A French physicist's masterpiece: How does the Fresnel zone plate work?
A Fresnel zone plate is a device that uses the principle of diffraction to focus light waves or any other wave characteristics. Unlike traditional lenses and curved mirrors, Fresnel zone plates focus on the diffraction of light rather than refraction or reflection. The core concept of this innovative technology originated from the analysis of French physicist Augustin-Jean Fresnel, so it is sometimes called Fresnel zone plate.
The focusing power of Fresnel area plates explores the phenomenon of Arago spots caused by opaque discs.
Fresnel zone plates consist of a set of concentric rings, also known as Fresnel zones, that alternate between opaque and transparent properties. When light hits this area plate, it bypasses the opaque area. The rings can be spaced just right so that the diffracted light interferes constructively at the desired focus, resulting in a sharp image.
Design and production
When designing and fabricating Fresnel zone plates, in order to obtain constructive interference at the focal point, the rings must switch from opaque to transparent at specific radial positions. This can be calculated according to the following formula:
rn = √((nλf) + 1/4 * n2λ2)
Among them, n is an integer, λ is the wavelength of light, and f is the distance from the center of the area plate to the focus. For small area boards, this formula can be simplified to
rn ≈ √(nλf).
For plates with multiple areas, the calculation of the focal length is simpler. The focal length f can be obtained through the radius rN of the outer circle area and its width ΔrN:
f = (2rNΔrN) / λ
With the improvement of production technology, the resolution of Fresnel area plates has also been enhanced. An effective production method is to use photolithography technology.
Application of regional board
Fresnel zone plates have a wide range of applications, especially when conventional lens materials cannot be used, especially for wavelengths such as X-rays. Fresnel zone plates are able to focus light of various wavelengths while filtering out unwanted wavelengths, making them popular in scientific research, especially in the field of physics.
Fresnel area plates focus light of multiple wavelengths, eliminating the need to look for transparent materials with different refractive indexes.
Use in photography
In photography, Fresnel zone plates can be used as a replacement for lenses or pinholes to produce unique soft-focus images. Compared with the small hole, the transparent area of the area plate is larger, which makes its effective aperture smaller than the small hole, thus shortening the exposure time.
This makes handheld shooting at higher ISO settings more feasible, especially in modern SLR digital cameras, making it even more convenient.
Other applications
In addition to photography, Fresnel area plates have other potential applications, such as as an affordable replacement in sights, or as imaging lenses under certain special aberration structures. The reflective properties of Fresnel area plates have also been used to focus radio waves, demonstrating their wide range of practicality.
In the field of image processing, the bitmap representation of the Fresnel area board can be used to test various image processing algorithms, which shows its potential value in software testing.
With the advancement of technology, the possibilities of Fresnel area boards seem to be constantly expanding. Are you also thinking about what other areas this technology can be applied to?
