Glan-Foucault prism

A Glan-Foucault prism (also called a Glan-air prism) is a type of 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 cemented together. [cite book |last=Bennett |first=Jean M . |editor=Bass, Michael, Ed. |title=Handbook of Optics Volume II |edition=2nd ed. |year=1995 |publisher=McGraw-Hill |isbn=0-07-047974-7 |pages=pp. 3.11–3.12 |chapter=Polarizers ] Total internal reflection of "p"-polarized light at the air gap means that only "s"-polarized light is transmitted straight through the prism.

Compared to the Glan-Thompson prism, the Glan-Foucault has a narrower acceptance angle over which it will work, but because it uses an air-gap rather than cement, much higher irradiances 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 100% polarized, the reflected beam is not.

The Glan-Taylor prism is very 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.cite journal | author=J-Y Fan "et al." | title=A study on transmitted intensity of disturbance for air-spaced Glan-type polarizing prisms | journal=Optics Communications | year=2003 | volume=223 | issue=1-3 | pages= 11–16 | doi=10.1016/S0030-4018(03)01618-3 ] Calcite Glan-Foucault prisms are now rarely used, having been mostly replaced by Glan-Taylor polarizers and other more recent designs.

YVO₄ 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 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.
class= G02B1/08; G02B27/28B; H01S3/00F] YVO₄ prisms are more expensive, however, and can accept beams over a very limited range of angles of incidence.

ee also

*Glan-Thompson prism
*Glan-Taylor prism

References