Optical window

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• In astronomy
  Astronomy
  
  Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
  , the optical window is the optical portion of the electromagnetic spectrum
  Electromagnetic spectrum
  
  The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object....
   that passes through the atmosphere
  Earth's atmosphere
  
  The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. Dry air contains roughly 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% Carbon dioxide in the Earth's atmosphere, and trace amounts of other gases....
   all the way to the ground. Most EM wavelengths are blocked by the atmosphere, so this is like a window that lets only a narrow selection of what is out there, though the Sun is particularly active in the passed wavelengths. It is called "optical" because the wavelengths we can see are all in this range. The window runs from around 300 nanometers (ultraviolet
  Ultraviolet
  
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 400 nanometer to 10 nm, and energies from 3 Electron volt to 124 eV....
  -C) at the short end up into the range the eye can use, roughly 400-700 nm and continues up through the visual infrared
  Infrared
  
  Infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves ....
   to around 1100 nm, which is thermal infrared. There are also infrared
  Infrared astronomy
  
  Infrared astronomy is the branch of astronomy and astrophysics which deals with objects visible in infrared radiation. Visible radiation ranges from 400 nanometre to 700 nm ....
   and "radio window
  Radio window
  
  The radio window is the range of frequencies of electromagnetic radiation that the earth's atmosphere lets through. The wavelengths in the radio window run from about one centimeter to about eleven-meter waves....
  s" that transmit some infrared
  Infrared
  
  Infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves ....
   and radio waves
  Radio waves
  
  Radio waves are Electromagnetic radiation occurring on the radio frequency portion of the electromagnetic spectrum....
  . The radio window runs from about one centimeter to about eleven-meter waves.

• In medical physics
  Medical physics
  
  File:Gamma knife.jpgMedical physics is the application of physics to medicine. It generally concerns physics as applied to medical imaging and radiotherapy, although a medical physicist may also work in many other areas of healthcare....
  , the optical window is the portion of the visible and infrared spectrum where living tissue absorbs relatively little light. This window runs approximately from 650 nm to 1200 nm. At shorter wavelengths light is strongly absorbed by hemoglobin
  Hemoglobin
  
  Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
   in blood, while at longer wavelengths water strongly absorbs infrared light.

• In optics, it means a (usually flat, sometimes optically flat
  Optical flat
  
  Optical flats are optical-grade glass structures lapping and polishing to be extremely flat on one or both sides, usually within a few millionths of an inch....
  ) piece of transparent (for a wavelength range of interest, not necessarily for visible light) optical material that allows light into an optical instrument
  Optical instrument
  
  An optical instrument either processes light waves to enhance an image for viewing, or analyzes light waves to determine one of a number of characteristic properties....
  . A window is usually parallel and is likely to be anti reflection coated
  Anti-reflective coating
  
  Anti-reflective or antireflection coatings are a type of optical coating applied to the surface of lens es and other optical devices to reduce reflection ....
  , at least if it is designed for visible light. An optical window may be built into a piece of equipment (such as a vacuum chamber) to allow optical instruments to view inside that equipment.

See also

• Radio window
  Radio window
  
  The radio window is the range of frequencies of electromagnetic radiation that the earth's atmosphere lets through. The wavelengths in the radio window run from about one centimeter to about eleven-meter waves....
  
• Atmospheric window
  Atmospheric window
  
  The atmospheric window refers to those parts of the electromagnetic spectrum that are, with the earth's atmosphere in its natural state, not absorbed at all....
  
• Astronomical window