polarimeter(redirected from polarimetric)
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polarimeter:see polarization of lightpolarization of light,
orientation of the vibration pattern of light waves in a singular plane. Characteristics of Polarization
Polarization is a phenomenon peculiar to transverse waves, i.e.
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(1) A device for measuring the angle of rotation of the plane of polarization of monochromatic light in optically active substances. (The dispersion of optical activity is
measured with spectropolarimeters.) In polarimeters constructed on the design of half-shadow devices (Figures 1 and 2), the measurement is made by a visual matching of the brightnesses of the two half-fields of light. Readings are then taken from an angular scale fitted with a vernier. This method, despite its fundamental simplicity, has a sufficiently high accuracy for many purposes, which accounts for the wide use of half-shadow polarimeters. More widespread, however, are the automatic polarimeters with photoelectric recorders. In these, the matching of the brightnesses is accomplished by modulating the plane of polarization of the entering light and isolating the signal of the
fundamental frequency as it emerges from the light detector (Figure 3). Modern automatic polarimeters permit measurements of the angle of optical rotation with an accuracy of ~0.0002°.
(2) A device for determining the amount of polarization p of partially polarized light. The simplest such polarimeter is the Cornu half-shadow polarimeter, designed for measuring the amount of linear polarization. A Wollaston prism and an analyzer are its main elements. Here, the brightnesses of the fields, illuminated by beams having different intensities upon emergence from the prism, are balanced by rotating the analyzer. The rotation scale is graduated for values of p. In the simple case of measuring the amount of linear polarization, a photoelectric polarimeter consists of a light detector and an analyzer that rotates about the optical axis of the polarimeter. The ratio of the amplitude of the alternative component to that of the direct component of the detector current is a direct measure of p. By placing a quarter-wave plate in front of the polarimeter, it is possible to measure the amount of circular polarization.
Polarimeters are widely used in the study of the structure and properties of substances and in the solution of technical problems. In particular, the measurement of the amount of circular polarization in radiation from stellar sources permits the detection of strong magnetic fields in the universe.
REFERENCEShishlovskii, A. A. Prikladnaia fizicheskaia optika. Moscow, 1961.
V. S. ZAPASSKII