Transverse X-ray Radiation from Petawatt-Laser-Driven Electron Acceleration in a Gas Cell

We measure X-rays emitted perpendicular to the laser propagation direction in petawatt-laser-driven wakefield acceleration of electrons in a gas cell. Multi-mega-electronvolt electrons are ejected in the transverse direction by laser-driven plasma wakefields, generating bremsstrahlung X-rays when they encounter a dense medium such as a gas-cell window. The X-rays, detected and characterized by two separate filter-stack spectrometers containing a series of imaging plates, exhibit peak energy fluences at ~ 150–200 keV. The mechanism of electron acceleration in the transverse direction and subsequent bremsstrahlung X-ray generation is also examined and confirmed using particle-in-cell and Monte Carlo FLUKA simulations.