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Direct laser acceleration (DLA) of electrons in a plasma of near-critical electron density (NCD) and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity (normalized laser amplitude a0 ≤ 4.3) and ps length pulse. This regime is typical of kJ PW-class laser facilities designed for high-energy-density (HED) research. In experiments at the PHELIX facility, it has been demonstrated that interaction of a 1019 W/cm2 sub-ps laser pulse with a sub-mm length NCD plasma results in the generation of high-current well-directed super-ponderomotive electrons with an effective temperature ten times higher than the ponderomotive potential [Rosmej et al., Plasma Phys. Controlled Fusion 62, 115024 (2020)]. Three-dimensional particle-in-cell simulations provide good agreement with the measured electron energy distribution and are used in the current work to study synchrotron radiation from the DLA-accelerated electrons. The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultrahigh photon number of 7 × 1011 in the 1–30 keV photon energy range at the focused laser energy of 20 J. Numerical simulations of betatron x-ray phase contrast imaging based on the DLA process for the parameters of a PHELIX laser are presented. The results are of interest for applications in HED experiments, which require a ps x-ray pulse and a high photon flux.
Radiative transition of an excited baryon to a nucleon with emission of a virtual massive photon converting to dielectron pair (Dalitz decays) provides important information about baryon-photon coupling at low q2 in timelike region. A prominent enhancement in the respective electromagnetic transition Form Factors (etFF) at q2 near vector mesons ρ/ω poles has been predicted by various calculations reflecting strong baryon-vector meson couplings. The understanding of these couplings is also of primary importance for the interpretation of the emissivity of QCD matter studied in heavy ion collisions via dilepton emission. Dedicated measurements of baryon Dalitz decays in proton-proton and pion-proton scattering with HADES detector at GSI/FAIR are presented and discussed. The relevance of these studies for the interpretation of results obtained from heavy ion reactions is elucidated on the example of the HADES results.