Polarization of bremsstrahlung at electron scattering in an anisotropic medium

TL;DR

This paper investigates how medium anisotropy affects bremsstrahlung radiation from relativistic electrons, revealing polarization effects and angular distributions that can be used to probe medium properties and generate polarized photon beams.

Contribution

It introduces a model where medium anisotropy is encapsulated by a vector $m N$, and analyzes its effects on radiation intensity, polarization, and angular distribution in bremsstrahlung.

Findings

Radiation polarization depends on emission angle and frequency.

Net polarization is proportional to $N^2/2$ and decreases with photon energy.

Complete polarization can occur at specific angles despite medium isotropy.

Abstract

Bremsstrahlung from relativistic electrons is considered under conditions when some transverse direction of momentum transfer is statistically preferred. It is shown that in the dipole approximation all the medium anisotropy effects can be accumulated into a special modulus-bound transverse vector, $\bm N$. To exemplify a target with $N^2\sim1$, we calculate radiation from electron incident at a small angle on an atomic row in oriented crystal. Radiation intensity and polarization dependence on the emission angle and frequency for constant $\bm N$ is investigated. Net polarization for the angle-integral cross-section is evaluated, which appears to be proportional to $N^2/2$, and decreases with the increase of the photon energy fraction. A prominent feature of the radiation angular distribution is the existence of an angle at which the radiation may be completely polarized, in spite of the target complete or partial isotropy -- that owes to existence of an origin-centered tangential circle for polarization in the fully differential radiation probability kernel. Possibilities for utilizing various properties of the polarized bremsstrahlung flux for preparation of polarized photon beams and for probing intrinsic anisotropy of the medium are analyzed.