In a plasma with a transverse density gradient, laser wavefront tilt develops gradually due to
phase velocity differences in different plasma densities. The wavefront tilt leads to a
parabolic trajectory of the plasma wakefield and hence the accelerated electron beam,
which leads to an angular streaking of the emitted betatron radiation. In this way, the
temporal evolution of the betatron X-ray spectra will be converted into angular “streak,” ie,
having a critical energy-angle correlation. An analytical model for the curved trajectory of a …