Glan-Taylor prism
The Glan-Taylor prism (after Paul Glan and AM Taylor ) is a polarizer based on birefringence and total reflection that linearly polarizes unpolarized light (p-polarization, i.e. the plane of polarization is in the plane of incidence). The principle was introduced by Paul Glan in 1880 and improved by AM Taylor in 1948.
The Glan-Foucault prism is basically constructed in the same way as the Glan-Taylor prism, but the section is rotated by 90 ° with respect to the optical axis of the calcite. This has the consequence that the transmitted beam is s-polarized.
construction
The Glan-Taylor prism, like the Nicol prism developed earlier (1828), consists of a birefringent crystal (typically calcite ), which is cut open along the diagonal surface parallel to the optical axis. The two halves are not joined together directly; an air gap between the prism parts provides interfaces to an optically thinner medium.
functionality
When entering a material, the incident light beam is refracted according to Snellius' law of refraction . Due to the anisotropic refractive indices of birefringent materials, the incident beam will behave differently depending on its polarization direction. A distinction is made between the ordinary (polarized perpendicular to the optical axis of the crystal) and the extraordinary (polarized parallel to the optical axis) beam.
At incidence at an angle to the optical axis , for example with the Nicol prism, these rays are refracted to different degrees. In the Glan-Taylor prism, the two calcite prisms are ground so that the cut surfaces of the crystal are parallel to the optical axis. In this way it is prevented that after the refraction of the incident ray, the ordinary and the extraordinary ray have different angles of refraction. In the case of perpendicular incidence, both parts of the beam move on a common path in the crystal, albeit at different speeds due to the different refractive indices.
The angle of intersection of the two halves of the prism is now selected so that the difference in refractive index between ordinary and extraordinary rays causes different reflection behavior at the interface with the air gap (total reflection and normal reflection / transmission). In the case of an optically negative birefringent material such as calcite, the refractive index for the ordinary ray is greater than that for the extraordinary ray. The angle of intersection lies between the critical angle of the ordinary and the critical angle of the extraordinary ray. When exiting the crystal, therefore, there is only the linearly polarized extraordinary ray whose plane of polarization lies in the plane of incidence and whose direction is unchanged with respect to the direction of incidence. The second prism (on the right in the figure) only serves to compensate for the deflection of the beam. For most materials (and wavelengths) the angle of intersection cannot be chosen so that the angle of incidence of the two rays equals the Brewster angle of the extraordinary ray. Therefore the (totally) reflected ray is not completely polarized, that is, it consists of the totally reflected ordinary ray and the reflected part of the extraordinary ray.
Differentiation from other types of prisms
The Glan-Thompson prism, which is also very similar (corresponds more to a Glan-Foucault prism with transparent adhesive instead of air), like the Glan-Foucault prism, generates a beam that is polarized differently by 90 ° (s-polarized).
The Lippich prism (after Ferdinand Franz Lippich (1838–1913)) has the same alignment of the optical axis as the Glan-Taylor prism, but does not have an air gap. Instead, the two prism parts were joined together with a transparent adhesive.
Individual evidence
- ↑ Paul Glan: About a polarizer . In: Carl's Repertory . No. 16 , 1880, p. 570 .
- ^ JF Archard, AM Taylor: Improved Glan-Foucault Prism . In: Journal of Scientific Instruments . tape 25 , no. 12 , 1948, pp. 407-409 , doi : 10.1088 / 0950-7671 / 25/12/304 .
- ↑ Gerd Litfin (Ed.): Technical optics in practice. 3rd edition, Springer, Berlin 2006, ISBN 3-540-21884-X , p. 58 ( limited preview in the Google book search).