polarimetrie

Polarimetry is the measurement and analysis of the polarization state of light. The polarization describes the orientation and ellipticity of the electric field oscillation and is commonly represented by Stokes parameters (I, Q, U, V). From these, the degree of polarization and the angle of polarization can be derived. Instruments include polarizers, waveplates, and detectors arranged to determine how light is modified by a sample or system. In French, the field is called polarimétrie.

Principle: Polarimetric techniques quantify changes in polarization caused by reflection, transmission, scattering, birefringence, or dichroism. In astronomy and remote sensing, polarimetry reveals information about magnetic fields, particle sizes, and surface textures. The analysis is often formalized with Mueller calculus or, in spectroscopic contexts, with the Stokes formalism.

Methods: Direct polarimetry uses sequences of measurements at different analyzer orientations to recover the Stokes parameters. Spectroscopic ellipsometry measures wavelength-dependent changes in polarization to determine optical constants and film thickness. Imaging polarimetry records spatially resolved polarization maps for complex samples.

Applications: In astronomy, polarimetry probes cosmic magnetic fields and scattering by dust. In chemistry and biology, it helps study chiral molecules and protein conformations. In materials science and engineering, photoelasticity uses polarization changes to reveal internal stresses. Remote sensing and quality control also rely on polarimetric information.

History and theory: The concept arose from studies of polarization by Malus and Brewster, with Stokes introducing a practical four-parameter description in the early 20th century. Since then, Mueller calculus and ellipsometry have extended polarimetry to complex media and thin films.