Figure 1

A typical bunch after its expulsion from the plasma edge for the case of \({a_0 = 100}\), \({\bar{n}_\mathrm{e} = 100}\). (a) The kinetic energy density. (b) The mean electron energy. Points with no data are white. The smooth variation in energy is a product of the quasi-monochromatic nature of the electron bunch as discussed in Ref.²². (c) The gamma spectrum of the electron bunch compared to that formed by a circularly polarised laser pulse. (d) The phase space transverse to bunch propagation in the x–y plane, namely, (\(x_\mathrm{T}\), \(p_\mathrm{T}\)) as defined in the “Methods” section. Again the dashed line marks the area defining the transverse normalised emittance. The skew of the ellipse is due to a low-density tail on the phase space beyond the bottom left corner of the plot.