Efficient Laser-Driven Radiation Sources in Relativistically Transparent Plasmas

Relativistically intense laser pulses are effective tools for driving high-fluence bursts of radiation, including ions and x-rays, in dense plasmas. Ion and x-ray yields are enhanced when plasma density approaches the relativistic-critical limit, beyond which the plasma is opaque to the laser drive. In this regime, laser-plasma interactions are subject to a range of nonlinear effects such as self-focusing and filamentation; however, the interaction physics can be simplified by considering the global transport of laser energy into ions and x-rays. Particle-in-cell (PIC) simulations and analytical modeling reveal that transmitted laser energy is a sufficient parameter to characterize key features of ion and x-ray radiation sources. In turn, a simple model relates transmitted energy with target density, providing a pathway to optimize targets to maximize ion and x-ray yields amidst complex microphysics.