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For photon energies from several 10 keV up to a few MeV Compton polarimetry is an indispensable tool to gain insight into subtle details of fundamental atomic radiative processes. Within the SPARC collaboration several segmented semiconductor detectors are developed that are well suited for application as efficient Compton polarimeters. In this report, these recent developments are reviewed and it is discussed how Compton polarimetry can be employed at the upcoming Gamma Factory. [ABSTRACT FROM AUTHOR]

A theoretical investigation of the resonant elastic scattering of laser photons by ultra‐relativistic partially stripped ions, that is the core process of the Gamma Factory project, is presented. Special emphasis in the study is placed on the angular distribution and polarization of scattered photons as observed in the collider and ion‐rest reference frames. In order to describe these (angular and polarization) properties for arbitrary relativistic many‐electron ion, the general approach, based on the application of irreducible polarization tensors, is laid down. By making use of the polarization tensors, the scattering of both conventional plane‐wave‐ and twisted (or vortex) photons is explored in detail. For the former case, it is shown how the propagation directions and polarization states of incident and outgoing photons are related to each other for the nS0→n′P1→nS0$n S_{0} \rightarrow n^{\prime } P_{1} \rightarrow n S_{0}$, nS1/2→n′P1/2→nS1/2$n S_{1/2} \rightarrow n^{\prime } P_{1/2} \rightarrow n S_{1/2}$, and nS1/2→n′P3/2→nS1/2$n S_{1/2} \rightarrow n^{\prime } P_{3/2} \rightarrow n S_{1/2}$ resonant transitions. For the scattering of initially twisted light that carries non‐zero orbital angular momentum, the angular distribution of secondary photons is explored and the conditions under which they are also twisted are discussed. [ABSTRACT FROM AUTHOR]

Scattering of light on relativistic heavy ion beams is widely used for characterizing and tuning the properties of both the light and the ion beam. Its elastic component—Rayleigh scattering—is investigated in this work for photon energies close to certain electronic transitions because of its potential usage in the Gamma Factory initiative at CERN. The angle-differential cross-section, as well as the degree of polarization of the scattered light are investigated for the cases of 1 s − 2 p 1 / 2 and 1 s − 2 p 3 / 2 resonance transitions in H-like lead ions. In order to gauge the validity and uncertainty of frequently used approximations, we compare different methods. In particular, rigorous quantum electrodynamics calculations are compared with the resonant electric-dipole approximation evaluated within the relativistic and nonrelativistic formalisms. For better understanding of the origin of the approximation, the commonly used theoretical approach is explained here in detail. We find that in most cases, the nonrelativistic resonant electric-dipole approximation fails to describe the properties of the scattered light. At the same time, its relativistic variant agrees with the rigorous treatment within a level of 10% to 20%. These findings are essential for the design of an experimental setup exploiting the scattering process, as well as for the determination of the scattered light properties. [ABSTRACT FROM AUTHOR]