Polarizers and Wave Plates
Polarizers select a polarization state and wave plates shift the relative phase of components, the basic tools for controlling polarized light.
Definition
Optical elements that act on polarization, with polarizers transmitting a selected polarization component and wave plates introducing a fixed phase retardation between orthogonal components to alter the state of polarization.
Scope
This topic covers the optical components used to produce, transform, and analyse polarized light. It includes dichroic and reflective polarizers and polarizing beam splitters, Malus's law for transmission through a polarizer, the action of wave plates (retarders) that introduce a controlled phase difference between orthogonal components, half-wave and quarter-wave plates and their use in rotating linear polarization or producing circular polarization, and the combination of these elements described by the Jones calculus. It treats the practical means of polarization control underlying many instruments.
Core questions
- How does a polarizer select a polarization and how much light does it transmit?
- How does a wave plate change the polarization state of light?
- How are half-wave and quarter-wave plates used in practice?
- How do combinations of these elements convert one polarization into another?
Key concepts
- polarizer
- Malus's law
- wave plate
- half-wave plate
- quarter-wave plate
- fast and slow axes
- polarizing beam splitter
- retardation
Key theories
- Malus's law
- When linearly polarized light passes through an ideal polarizer, the transmitted intensity equals the incident intensity times the square of the cosine of the angle between the polarization and the polarizer's transmission axis.
- Wave-plate retardation
- A birefringent plate introduces a phase difference between the components along its fast and slow axes; a half-wave plate rotates linear polarization while a quarter-wave plate converts between linear and circular polarization.
Clinical relevance
Polarizers and wave plates are core components of polarized-light microscopes used in diagnostic pathology, of polarimeters that measure optically active analytes such as glucose, and of the liquid-crystal devices that control light in displays and ophthalmic instruments.
History
Malus established his intensity law in 1809, and Nicol devised the calcite polarizing prism that bears his name in 1828. Practical sheet polarizers became widely available after Edwin Land invented dichroic polarizing film in the 1930s, founding the Polaroid Corporation.
Key figures
- Étienne-Louis Malus
- William Nicol
- Edwin Land
Related topics
Seminal works
- hecht2017
- salehteich2019
Frequently asked questions
- How much light passes through two crossed polarizers?
- Ideally none; when the transmission axes are perpendicular, Malus's law gives zero transmission because the cosine of ninety degrees is zero, which is why crossed polarizers appear dark.
- How does a quarter-wave plate make circularly polarized light?
- If linearly polarized light enters at forty-five degrees to the plate's axes, the plate delays one component by a quarter wavelength relative to the other, and the two equal-amplitude components combine into circular polarization.