Polarisator

A polarisator, also known as a polarizer, is an optical device that transmits light with a selected polarization and attenuates or blocks other polarizations. It is used to create, analyze, or maintain polarized light in scientific and practical applications.

Types include linear polarizers, which pass one linear polarization orientation while absorbing or reflecting the orthogonal component; circular polarizers, which combine a linear polarizer with a quarter-wave plate to produce or analyze circular polarization; and more complex polarizing beam-splitter arrangements that separate polarization components. Polarizers may be absorptive, reflective, or based on birefringent or dielectric stack designs. The performance is often characterized by the extinction ratio, transmittance, and spectral bandwidth; circular polarizers are sensitive to wavelength and geometry.

Common implementations rely on dichroic polymer films (for example, stretched polyvinyl alcohol with iodine) or crystalline materials and dielectric coatings. Some polarizers use birefringent components such as Wollaston or Wollaston-like prisms to split light into polarization components, while others rely on multilayer dielectric coatings to achieve high transmission in a target band.

Applications span photography and cinematography to reduce glare, liquid crystal displays, optical instrumentation, spectroscopy, microscopy, astronomy, and fiber-optic communications. In research, polarisators are essential for methods that measure polarization states, such as polarimetry, ellipsometry, and spin-resolved spectroscopy.

Historically, polarized light devices emerged in the early 20th century, with significant developments leading to commercial polarizers produced by companies such as the Polaroid Corporation. Modern polarizers cover a broad range of wavelengths from the ultraviolet to the infrared and are integrated into many optical systems.