Glan-Foucault prism.html



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 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.¹ 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.² 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.³ YVO₄ prisms are more expensive, however, and can accept beams over a very limited range of angles of incidence.

See also

• Glan-Thompson prism
• Glan-Taylor prism

References

1. ^ Bennett, Jean M . (1995). "Polarizers", in Bass, Michael, Ed.: Handbook of Optics Volume II, 2nd ed., McGraw-Hill, pp. 3.11–3.12. ISBN 0-07-047974-7. 
2. ^ J-Y Fan et al. (2003). "A study on transmitted intensity of disturbance for air-spaced Glan-type polarizing prisms". Optics Communications 223 (1-3): 11–16. doi:10.1016/S0030-4018(03)01618-3. 
3. ^ US patent 3914018, "Yttrium orthovanadate optical polarizer", granted 1975-10-21, assigned to Union Carbide Corp.