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{{Short description|Type of polarizer}}
[[Image:Glan-foucault.png|frame|right|A Glan–Foucault prism deflects ''p''-polarized light, transmitting the ''s''-polarized component. The optical axis of the prism material is perpendicular to the plane of the diagram.]]
A '''Glan–Foucault prism''' (also called a '''Glan–air prism''') is a type of [[prism (optics)|prism]] which is used as a [[polarizer]]. It is similar in construction to a [[Glan–Thompson prism]], except that two right-angled [[calcite]] prisms are spaced with an air gap instead of being cemented together.<ref>{{cite book |last=Bennett |first=Jean M. |editor=Bass Michael, Ed. |title=Handbook of Optics Volume II |edition=2nd |date=1995 |publisher=[[McGraw-Hill]] |isbn=0-07-047974-7 |pages=3.11–3.12 |chapter=Polarizers }}</ref> [[Total internal reflection]] of ''p''-[[polarization (waves)|polarized]] light at the air gap means that only ''s''-polarized light is transmitted straight through the prism.
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Compared to the Glan–Thompson prism, the Glan–Foucault has a narrower acceptance angle over which it works, but because it uses an air gap rather than cement, much higher [[irradiance]]s can be used without damage. The prism can thus be used with [[laser]] beams. The prism is also shorter (for a given usable aperture) than the Glan–Thompson design, and the deflection angle of the rejected beam can be made close to 90°, which is sometimes useful. Glan–Foucault prisms are not typically used as polarizing beamsplitters because while the transmitted beam is completely polarized, the reflected beam is not.
The [[Glan–Taylor prism]] is similar, except that the crystal axes and transmitted polarization direction are orthogonal to the Glan–Foucault design. This yields higher transmission and better polarization of the reflected light.<ref name=Fan>{{cite journal | author=J.-Y. Fan | display-authors=etal | title=A study on transmitted intensity of disturbance for air-spaced Glan-type polarizing prisms | journal=Optics Communications | date=2003 | volume=223 | issue=1–3 | pages= 11–16 | doi=10.1016/S0030-4018(03)01618-3 |arxiv = physics/0211045 |bibcode = 2003OptCo.223...11F | s2cid=119094515 }}</ref> Calcite Glan–Foucault prisms are now rarely used, having been mostly replaced by Glan–Taylor polarizers and other more recent designs.
[[Yttrium orthovanadate]] (YVO<sub>4</sub>) prisms based on the Glan–Foucault design have superior polarization of the reflected beam and higher damage threshold, compared with calcite Glan–Foucault and Glan–Taylor prisms.<ref>{{Cite patent |country= US |number= 3914018 |status= patent |title= Yttrium orthovanadate optical polarizer |gdate= 1975-10-21 |fdate= 1973-11-20 |invent1= Deshazer, Larry G. |assign1= Union Carbide Corp.}}</ref> YVO<sub>4</sub> prisms are more expensive, however, and can accept beams over a very limited range of angles of incidence.
▲[[Category:Polarization]]
==References==
[[Category:Prisms]]▼
{{reflist}}
{{DEFAULTSORT:Glan-Foucault prism}}
[[Category:Polarization (waves)]]
▲[[Category:Prisms (optics)]]
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