polarisimetrie

Polarisimetrie, or polarimetry in English, is the measurement of the polarization state of light and how it is modified by a material or an optical process. The primary observable is a change in polarization, which can be a rotation of the polarization plane, a change in ellipticity, or a more general alteration of the polarization state.

Principles and concepts in polarisimetrie involve representing polarization with formalisms such as Stokes parameters and Mueller matrices or, in some cases, Jones calculus. A sample that is optically active can rotate the plane of polarization of linearly polarized light, a phenomenon known as optical rotation. The degree of rotation is often reported as specific rotation, [α], which relates the measured rotation to the path length and the concentration of the chiral substance. Polarimetry can also characterize birefringence and other polarization-altering effects in materials.

Instruments and methods include polarimeters that analyze the rotation of polarized light after it passes through a sample, typically using a polarizer, an analyzer, and a detector. Modern polarimetry often employs automatic rotation, spectropolarimetry across wavelengths, or ellipsometry, which detects changes in polarization upon reflection to determine thin-film thickness and optical constants. The mathematical frameworks of Stokes and Mueller calculus enable analysis of complex samples and multi-parameter measurements.

Applications of polarisimetrie span chemistry, pharmaceuticals, and biochemistry for determining enantiomeric purity and concentrations of chiral compounds; food and agricultural quality control; materials science for stress analysis and crystal orientation; and astronomy for studying polarized light from celestial sources and interstellar media.