[Paper Review] Polarization and Polarimetry: A Review

Sascha Trippe|arXiv (Cornell University)|Jan 9, 2014

Astrophysics and Cosmic Phenomena5 references4 citations

TL;DR

This comprehensive review synthesizes the physics, observational techniques, and astrophysical applications of polarization in astronomy. It details how polarization arises from electromagnetic wave properties, photon behavior, and interactions with matter—such as scattering, synchrotron radiation, and magnetic field effects—while outlining methods from radio to gamma-ray wavelengths and highlighting key science cases from solar physics to cosmic microwave background polarization, especially E and B modes linked to cosmic inflation.

ABSTRACT

Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, Goldreich-Kylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and X/gamma wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.

Motivation & Objective

• To provide a unified, up-to-date overview of polarization physics and its role in astrophysical diagnostics.
• To clarify the physical origins of polarization in diverse astrophysical environments, including scattering, magnetic fields, and radiation-matter interactions.
• To systematize observational techniques across radio, optical, and high-energy wavelengths, addressing instrumental and atmospheric challenges.
• To highlight the unique astrophysical insights polarization provides that are inaccessible through photometry, spectroscopy, or imaging alone.
• To emphasize emerging opportunities in X/γ-ray polarimetry and optical interferometric polarimetry for future discoveries.

Proposed method

• Uses Maxwell's equations and wave theory to describe electromagnetic polarization, focusing on electric field vector behavior in space and time.
• Applies quantum mechanical concepts to photons, particularly their spin and helicity, to explain polarization at the quantum level.
• Employs three formalisms—Jones calculus, Stokes parameters, and Müller formalism—for mathematical representation and transformation of polarized states.
• Analyzes polarization generation mechanisms: scattering (dust, electrons), synchrotron radiation, Zeeman, Goldreich–Kylafis, and Hanle effects.
• Considers polarization-matter interactions such as Faraday rotation, birefringence, and Chandrasekhar–Fermi effects, including depolarization processes.
• Reviews observational strategies, including sky projection geometry, atmospheric and instrumental polarization corrections, and statistical methods for low-signal regimes.

Experimental results

Research questions

• RQ1 How do electromagnetic wave properties and photon spin give rise to observable polarization states in astrophysical sources?
• RQ2 What physical mechanisms generate polarization in different astrophysical environments, such as scattering media, magnetic plasmas, and relativistic outflows?
• RQ3 How do polarization measurements constrain magnetic fields, particle distributions, and radiation anisotropies in objects from stars to the early universe?
• RQ4 What are the key observational challenges in measuring polarization across radio, optical, and X/γ-ray bands, and how are they addressed?
• RQ5 To what extent can polarization, especially B-mode CMB polarization, probe primordial gravitational waves and cosmic inflation?

Key findings

• Polarization is fundamentally linked to the internal geometry of radiation sources, providing unique insights into magnetic fields, scattering geometry, and plasma conditions.
• Scattering by dust grains and electrons produces significant linear polarization, especially in circumstellar envelopes, planetary atmospheres, and the solar corona.
• Synchrotron radiation from relativistic electrons in magnetic fields is a dominant source of polarized emission in radio and X-ray bands.
• The Zeeman, Goldreich–Kylafis, and Hanle effects enable direct magnetic field measurements in stars and interstellar media via polarization signatures.
• Faraday rotation and depolarization are critical effects in magnetized plasmas, limiting but also informing polarimetric observations in the interstellar medium.
• E and B mode polarization of the cosmic microwave background (CMB) are key probes of primordial gravitational waves and scalar perturbations, with E modes detected and B modes recently observed at sub-microkelvin levels.