Spectropolarimetric

Spectropolarimetric measurements combine spectroscopy and polarimetry to observe the polarization state of light across a spectrum. They record the full set of Stokes parameters I, Q, U, and V as a function of wavelength, producing spectropolarimetric data that encode information about magnetic fields, scattering, and grain alignment. Polarization signals may arise from Zeeman splitting in magnetized atmospheres, scattering in stellar or planetary atmospheres, or dichroic extinction by aligned dust grains, allowing the study of physical conditions inaccessible in intensity spectra alone.

Instrumentation and methods: Modern spectropolarimetric instruments integrate a spectrograph with polarization optics such as rotating waveplates or modulators, polarizers, and beam-splitting prisms to separate polarization states. A dual-beam configuration is common to reduce seeing and instrumental variability. Calibration for instrumental polarization and telescope effects is essential, and data reduction yields wavelength-dependent Stokes spectra. Inversions of spectropolarimetric data, using models like Milne-Eddington or Zeeman-Doppler imaging, infer magnetic fields, velocity fields, and atmospheric parameters.

Applications: In solar physics, spectropolarimetry maps solar magnetic fields in the photosphere and chromosphere. In stellar astrophysics, it probes magnetism in other stars and their circumstellar environments. In planetary science and astronomy, it helps characterize scattering geometries and dust properties in disks and exoplanetary systems. In atmospheric remote sensing, spectropolarimetry informs aerosol properties and surface reflectance. Related techniques in condensed matter physics study magneto-optical effects in materials, illustrating the broader use of polarization-sensitive spectroscopy.