Optical flat

Optical flat
Optical flats in case. About 1 inch (2.5 cm) in diameter
Testing flatness of surfaces with optical flats. The lefthand surface is flat, the righthand surface is uneven.

Optical flats are optical-grade pieces of glass lapped and polished to be extremely flat on one or both sides, usually within a few millionths of an inch (about 25 nanometres). They are used with a monochromatic light to determine the flatness of other optical surfaces by interference.[1] When an optical flat is placed on another surface and illuminated, the light waves reflect off both the bottom surface of the flat and the surface it is resting on. The reflected waves interfere, creating a pattern of interference fringes (Newton's rings), visible as light and dark bands. The spacing between the fringes is smaller where the gap is changing more rapidly, indicating a departure from flatness in one of the two surfaces, in a similar way to the contour lines on a map. A flat surface is indicated by a pattern of straight, parallel fringes with equal spacing, while other patterns indicate uneven surfaces. Two adjacent fringes indicate a difference in elevation of one-half wavelength of the light used, so by counting the fringes differences in elevation of the surface can be measured to millionths of an inch.

Usually only one of the two surfaces is made optically flat to the specified tolerance, and this surface is indicated by an arrow on the edge of the glass.

Optical flats are sometimes given an optical coating and used as precision mirrors for special purposes, such as in a Fabry–Pérot interferometer or laser cavity. Optical flats have uses in spectrophotometry as well.

Optical flats being used to calibrate metal parts.

See also

References

  1. ^ English, R. E. (1953). "Optical Flats". In Ingalls, Albert G.. Amateur Telescope Making, Book Three. Scientific American. pp. 156–162. 



Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • optical flat — a glass plate so perfectly flat that only an interferometer can measure its unevenness …   Medical dictionary

  • optical flat — noun : flat 6 a …   Useful english dictionary

  • optical flat — noun a disk of high quality quartz glass having at least one side ground and polished with a deviation in flatness less than 50 nanometers all over, and a surface quality of 5 microfinish or less; used, in an interferometer, to measure the… …   Wiktionary

  • Optical disc — Optical media redirects here. For transmission media for light, see Medium (optics). The optical lens of a compact disc drive. In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes… …   Wikipedia

  • Optical cross section — or OCS is a value which describes the maximum amount of optical flux reflected back to the source. The standard unit of measurement is . It is dependent on the geometry and the reflectivity at a particular wavelength of an object. Optical cross… …   Wikipedia

  • Optical tweezers — (originally called single beam gradient force trap ) are scientific instruments that use a highly focused laser beam to provide an attractive or repulsive force (typically on the order of piconewtons), depending on the refractive index mismatch… …   Wikipedia

  • Flat-field correction — is a technique used to improve quality in digital imaging. The goal is to remove artifacts from 2 D images that are caused by variations in the pixel to pixel sensitivity of the detector and/or by distortions in the optical path. It is a standard …   Wikipedia

  • Optical contact bonding — is a glueless process whereby two closely conformal surfaces are joined together, being held purely by intermolecular forces. Contents 1 History 2 Explanation 3 Production of an optical contact bond 4 …   Wikipedia

  • Optical lift — is an optical analogue of aerodynamic lift, in which a cambered refractive object with differently shaped top and bottom surfaces experiences a stable transverse lift force when placed in a uniform stream of light.[1] Contents 1 Discovery 2… …   Wikipedia

  • Flat glass — Flat glass, sheet glass, or plate glass is a type of glass, initially produced in plane form, commonly used for windows, glass doors, transparent walls, and windshields. For modern architectural and automotive applications, the flat glass is… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”