LLE Review, Volume 118 68 Laser-generated relativistic electron beams have applications in compact, high-brightness laser–plasma particle accelerators,1 narrowband x-ray sources for medical applications,2 x-ray sources for ignition-scale, high-density inertial confinement fusion (ICF) target backlighter radiography,3 collimated electron beams for free-electron lasers,4 and collimated electron b...