High brightness betatron x-ray source driven by chirped laser pulses

We demonstrate high brightness betatron x-ray generation from chirped laser pulses driven plasma accelerator. It is shown that positively chirped laser pulse leads to the initiation and enhancement of collective oscillations of electrons inside plasma bubble, due to associated pulse front tilt (PFT). The PFT causes transverse drift of the bubble with respect to the laser axis, which results in high brightness x-ray generation. At an optimum chirp, enhanced x-ray emission of >108 photons/pulse/sr in 0.1% BW with a critical energy of similar to 18 keV was observed by a factor >2 in comparison to the case of no chirp. The role of collective oscillation in enhancing x-ray emission is also validated in the Geant4 simulations.