Төмендеу толқындарының поляризациясын өлшеу және интерпретациялау

Measurement and interpretation of the polarization of transverse waves

Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or have been reflected, refracted or diffracted by some material in order to characterize that object. Plane polarized light: According to the wave theory of light, an ordinary ray of light is considered to be vibrating in all planes of right angles to the direction of its propagation. If this ordinary ray of light is passed through a nicol prism, the emergent ray has its vibration only in one plane.

Polarimetry of thin films and surfaces is commonly known as ellipsometry. Polarimetry is used in remote sensing applications, such as planetary science, astronomy, and weather radar. Polarimetry can also be included in computational analysis of waves. For example, radars often consider wave polarization in post processing to improve the characterization of the targets. In this case, polarimetry can be used to estimate the fine texture of a material, help resolve the orientation of small structures in the target, and, when circularly polarized antennas are used, resolve the number of bounces of the received signal (the chirality of circularly polarized waves alternates with each reflection).

In 2003, a visible near IR (VNIR) Spectropolarimetric Imager with an acousto optic tunable filter (AOTF) was reported. VNIR and LWIR hyperspectral imaging consistently perform better as hyperspectral imagers. This technology was developed at the U. S. Army Research Laboratory.

Gemologists use polariscopes to identify various properties of gems under examination. Proper examination may require the gem to be inspected in various positions and angles. A gemologist's polariscope is a vertically oriented device, usually with two polarizing lenses with one over the other with some space in between. A light source is built into the polariscope underneath the bottom polarizing lens and pointing upwards. A gemstone will be placed on top of the lower lens and may be properly examined by looking down at it through the top lens. To operate the polariscope, a gemologist may turn the polarizing lenses by hand to observe various characteristics about a gemstone. Polariscopes make use of their polarizing filters to reveal properties of a gem about how it affects light waves passing through it. A polariscope may be first used to determine the optic character of a gem and whether it is singly refracting (isotropic), anomalously doubly refracting (isotropic), doubly refracting (anisotropic), or aggregate. If the stone is doubly refracting and is not an aggregate, the polariscope may be used to further determine the optic figure of the gemstone, or whether it is uniaxial or biaxial. This step may require use of a loupe, also known as a conoscope. Finally, a polariscope can be used to detect the pleochroism of a gemstone, although a dichroscope may be preferred for this purpose as it may show pleochroic colors side by side for easier identification.

A polarimeter is the basic scientific instrument used to make these measurements, although this term is rarely used to describe a polarimetry process performed by a computer, such as is done in polarimetric synthetic aperture radar. Polarimetry can be used to measure various optical properties of a material, including linear birefringence, circular birefringence (also known as optical rotation or optical rotary dispersion), linear dichroism, circular dichroism and scattering. To measure these various properties, there have been many designs of polarimeters, some archaic and some in current use. The most sensitive are based on interferometers, while more conventional polarimeters are based on arrangements of polarising filters, wave plates or other devices.

Polarimetry is used in many areas of astronomy to study physical characteristics of sources including active galactic nuclei and blazars, exoplanets, gas and dust in the interstellar medium, supernovae, gamma ray bursts, stellar rotation, stellar magnetic fields, debris disks, reflection in binary stars and the cosmic microwave background radiation. Astronomical polarimetry observations are carried out either as imaging polarimetry, where polarization is measured as a function of position in imaging data, or spectropolarimetry, where polarization is measured as a function of wavelength of light, or broad band aperture polarimetry.