Craig J. A. Millar | Searcharxiv

arXiv2026

Spatio-spectral vector light created by optical activity in rubidium vapor

We show that optical activity in atomic media can generate multidimensional correlations in frequency, polarization and spatial degrees of freedom, allowing us to observe frequency shifts as image rotations. Specifically, we demonstrate a pump-probe scheme, where optical pumping with circularly polarized light generates macroscopic magnetization in an atomic vapor, associated with frequency-dependent circular dichroism and birefringence. A vortex probe beam, characterized by spatially varying polarization, maps this optical activity onto the spatial structure of the transmitted light. Measuring the intensity profile in a suitable polarization component then allows us to perform spatially resolved polarization spectroscopy. On resonance we observe a rotation with a slope in the order of 98 mrad per MHz. These findings may find applications in image-based laser-locking, high-precision spectroscopy, magnetometry, and the generation of hybrid entanglement.

physics.atom-ph↗

arXiv2026

Transformation of vector modes by the Faraday effect in strong magnetic fields

Large Faraday rotations can be generated by circular birefringence of atomic samples in an axial magnetic field in the vicinity of atomic resonance lines. The Faraday angle is a function of the magnetic field strength, the optical density of the atomic sample which may be varied by changing the temperature of the atomic gas, and of course the optical detuning from the transition frequencies. More generally, magneto-optical effects in atomic samples include circular dichroism in addition to birefringence, resulting in a modification of the ellipticity as well as the polarisation alignment. Usually such effects are investigated for homogeneous linear polarisations, but the mechanisms apply also to polarisation structures such as vector vortices. We investigate the effect of optical activity of a rubidium vapour in the Hyperfine Paschen-Back regime, for the example of an azimuthally polarised input light beam. We show that for low atomic densities, circular birefringence dominates over dichroism, and azimuthal polarisation is rotated towards radial polarisation. The rotation angle increases with increasing optical densities. At high vapour temperatures, dichroism becomes more and more relevant, leading to intricate variations of both alignment and ellipticity.

physics.atom-ph↗