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Polarimetry is the measurement and interpretation of the polarization of , most notably electromagnetic waves, such as Radio wave or . 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.
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).
The researchers reported visible near infrared system (VISNIR) data (.4-.9 micrometers) which required an RF signal below 1 W power. The reported experimental data indicates that polarimetric signatures are unique to manmade items and are not found in natural objects. The researchers state that a dual system, collecting both hyperspectral and spectropolarimetric information, is an advantage in image production for target tracking.
Polarimetric infrared imaging and detection can also highlight and distinguish different features in a scene and give unique signatures of different objects. A nano-plasmonic chirped metal structure for polarimetric detection in the mid-wave and long-wave infrared dual bands can give unique characteristics about the different detected materials, objects, and surfaces.
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.
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), 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 , while more conventional polarimeters are based on arrangements of Polarizer, or other devices.
In ordinary light, the vibrations occur in all planes perpendicular to the direction of propagation. When light passes through a Nicol prism its vibrations in all directions except the direction of axis of the prism are cut off. The light emerging from the prism is said to be plane polarised because its vibration is in one direction. If two Nicol prisms are placed with their polarization planes parallel to each other, then the light rays emerging out of the first prism will enter the second prism. As a result, no loss of light is observed. However, if the second prism is rotated by an angle of 90°, the light emerging from the first prism is stopped by the second prism and no light emerges. The first prism is usually called the polarizer and the second prism is called the analyser.
A simple polarimeter to measure this rotation consists of a long tube with flat glass ends, into which the sample is placed. At each end of the tube is a Nicol prism or other polarizer. Visible light is shone through the tube, and the prism at the other end, attached to an eye-piece, is rotated to arrive at the region of complete brightness or that of half-dark, half-bright or that of complete darkness. The angle of rotation is then read from a scale. The same phenomenon is observed after an angle of 180°. The specific rotation of the sample may then be calculated. Temperature can affect the rotation of light, which should be accounted for in the calculations.
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