Imaging electron trajectories in a laser-wakefield cavity using betatron x-ray radiation

We demonstrate that betatron x-ray radiation accurately provides direct imaging of electrons trajectories accelerated in laser wakefields. Experimental far field x-ray beam profiles reveal that electrons can follow similar transverse trajectories with typical excursions of 1.5 mu m +/- 0.5 mu m in the plane of laser polarization and 0.7 mu m +/- 0.2 mu m in the plane perpendicular.