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A Fresnel lens ( / ˈfreɪnɛl, - nəl / FRAY-nel, -nəl; / ˈfrɛnɛl, - əl / FREN-el, -əl; or / freɪˈnɛl / fray-NEL[ 1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
A zone plate is a device used to focus light or other things exhibiting wave character. [ 1] Unlike lenses or curved mirrors, zone plates use diffraction instead of refraction or reflection. Based on analysis by French physicist Augustin-Jean Fresnel, they are sometimes called Fresnel zone plates in his honor.
Fresnel diffraction. In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. [ 1] It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when ...
The Fresnel number is a useful concept in physical optics. The Fresnel number establishes a coarse criterion to define the near and far field approximations. Essentially, if Fresnel number is small – less than roughly 1 – the beam is said to be in the far field. If Fresnel number is larger than 1, the beam is said to be near field.
The Huygens–Fresnel principle (named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel) states that every point on a wavefront is itself the source of spherical wavelets, and the secondary wavelets emanating from different points mutually interfere. [ 1 ] The sum of these spherical wavelets forms a new ...
Physics of optical holography. Optical holography[ 1] is a technique which enables an optical wavefront to be recorded and later re-constructed. Holography is best known as a method of generating three-dimensional images but it also has a wide range of other applications .
The new all-white lighthouse tower was completed in 1868, receiving a first-order Fresnel lens made by Henry-Lepaute and Company of Paris, France that was first lit on May 10, 1868. [ 1 ] [ 6 ] The lower three levels of the tower served as the living quarters for the keepers and his assistants complete with kitchen, living room and bedrooms.
Little is known of the first front range light. In 1879 a new front range beacon was erected 448 feet (137 m) southeast of the light tower. This light, known as the Pensacola Bar Beacon, was a square pyramidal wooden tower, 26 feet (7.9 m) tall, sitting on a point 29 feet (8.8 m) above sea level, so that the light was 55 feet (17 m) above the ...