Ultra-high brilliance multi-MeV $\gamma$-ray beam from non-linear   Thomson scattering
  We report on the generation of a narrow divergence ($\theta\approx 2.5$ mrad), multi-MeV ($E_\text{MAX} = 18$ MeV) and ultra-high brilliance ($\approx 2\times10^{19}$ photons s$^{-1}$ mm$^{-2}$ mrad $^{-2}$ 0.1\% BW) $\gamma$-ray beam from the scattering of an ultra-relativistic laser-wakefield accelerated electron beam in the field of a relativistically intense laser (dimensionless amplitude $a_0\approx2$). The spectrum of the generated $\gamma$-ray beam is measured, with MeV resolution, seamlessly from 6 MeV to 18 MeV, giving clear evidence of the onset of non-linear Thomson scattering. The photon source has the highest brilliance in the multi-MeV regime ever reported in the literature. 
G. Sarri, D. J. Corvan, W. Schumaker, J. Cole, A. Di Piazza, H. Ahmed,   C. Harvey, C. H. Keitel, K. Krushelnick, S. P. D. M...
physics.optics physics.plasm-ph