A Glan–Thompson prism is a type of
polarizing prism
PRISM is a code name for a program under which the United States National Security Agency (NSA) collects internet communications from various U.S. internet companies. The program is also known by the SIGAD . PRISM collects stored internet ...
similar to the
Nicol prism
A Nicol prism is a type of polarizer. It is an optical device made from calcite crystal used to convert ordinary light into plane polarized light. It is made in such a way that it eliminates one of the rays by total internal reflection, i.e. ...
and
Glan–Foucault prism.
Design
A Glan–Thompson prism consists of two right-angled
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
prisms that are cemented together by their long faces. The
optical axes of the calcite crystals are parallel and aligned perpendicular to the plane of reflection.
Birefringence
Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefrin ...
splits light entering the prism into two rays, experiencing different
refractive indices
In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
; the ''p''-polarized
ordinary ray is
totally internally reflected from the calcite–cement interface, leaving the ''s''-polarized
extraordinary ray to be transmitted. The prism can therefore be used as a
polarizing beam splitter
A beam splitter or beamsplitter is an optical instrument, optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as Interferometry, int ...
.
Traditionally
Canada balsam
Canada balsam, also called Canada turpentine or balsam of fir, is the oleoresin of the balsam fir tree (''Abies balsamea'') of boreal North America. The resin, dissolved in essential oils, is a viscous, sticky, colourless or yellowish liquid t ...
was used as the cement in assembling these prisms, but this has largely been replaced by synthetic polymers.
Characteristics
Compared to the similar Glan–Foucault prism, the Glan–Thompson has a wider acceptance angle, but a much lower limit of maximal
irradiance
In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (symbol W⋅m−2 or W/m2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) ...
(due to optical damage limitations of the cement layer).
See also
*
Glan–Taylor prism
References
{{DEFAULTSORT:Glan-Thompson prism
Polarization (waves)
Prisms (optics)