optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

, a window is an optical element that is transparent to a range of

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

s, and that has no

optical power In optics, optical power (also referred to as dioptric power, refractive power, focal power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the ...

. Windows may be flat or curved. They are used to block the flow of air or other fluids while allowing light to pass into or out of an optical system.

General characteristics

In general, an optical window is a material that allows light into an

optical instrument An optical instrument is a device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscopes, telescopes, and camera ...

. The material has to be transparent to a wavelength range of interest but not necessarily to visible light. Usually, it is mechanically flat and sometimes it also is optically flat, depending on resolution requirements. A window of this sort is commonly parallel and is likely to be anti-reflection coated, especially if it is designed for visible light. An optical window may be built into a piece of equipment (such as a

vacuum chamber A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. This results in a low-pressure environment within the chamber, commonly referred to as a vacuum. A vacuum environment allows researchers to c ...

) to allow optical instruments to view inside that equipment.

In spectroscopy

Optical windows used for UV/VIS spectroscopy, are usually made from

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

fused silica Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses, such as soda-lime glass, lead glass, or borosil ...

. In

IR spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...

, there is a wide range of materials that transmit light into the

far infrared Far infrared (FIR) or long wave refers to a specific range within the infrared spectrum of electromagnetic radiation. It encompasses radiation with wavelengths ranging from 15 μm ( micrometers) to 1 mm, which corresponds to a freque ...

and can be utilized for the construction of optical windows, from barium fluoride (BaF₂), calcium fluoride, potassium bromide, potassium chloride, sodium chloride,

germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...

(Ge),

zinc selenide Zinc selenide is the inorganic compound with the formula ZnSe. It is a lemon-yellow solid although most samples have a duller color due to the effects of oxidation. It is an intrinsic semiconductor with a band gap of about 2.70 eV at , equi ...

(ZnSe) and

sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name ''sapphire ...

. These windows are either built into

circular Circular may refer to: * The shape of a circle * ''Circular'' (album), a 2006 album by Spanish singer Vega * Circular letter (disambiguation), a document addressed to many destinations ** Government circular, a written statement of government pol ...

, elliptical or

rectangular In Euclidean plane geometry, a rectangle is a rectilinear convex polygon or a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90 ...

configurations.{{Cite book, last1=Vukobratovich, first1=Daniel, url=http://www.worldcat.org/oclc/1020287047, title=Fundamentals of Optomechanics, last2=Yoder, first2=Paul, publisher=CRC Press, year=2018, isbn=978-1-4987-7075-0, pages=64, oclc=1020287047 , language=en

References

Optical components