Superbright laser source of gamma radiation based on the betatron mechanism

We consider the generation of synchrotron radiation in a near-critical density plasma in the regime of relativistic self-trapping of a propagating laser pulse as applied to the parameters of the XCELS facility. This regime of propagation ensures the acceleration of electrons with an extremely large total charge (at a level of several tens of nanocoulombs) to gigaelectronvolt energies, which determines the very high brightness of synchrotron radiation. On the basis of the calculation of retarded potentials, we study the space–time and spectral–angular characteristics of secondary gamma radiation. It is shown that laser pulses from the XCELS facility will make it possible to generate directed secondary radiation with photon energies up to 10 MeV (and higher) and a brightness exceeding 10²³ photons·s^–1·mm^–2·mrad^–2 (at Δλ/λ = 0.1 %), which turns out to be greater than the brightness of the bremsstrahlung gamma source for the same laser parameters. This opens up prospects for using a betatron source for phase-contrast microscopy of deeply shielded objects.