Stable Beam Propagation for Efficient MeV Photon Dose Generation in Laser–Solid Interactions

Analytical and numerical models indicate that x-ray dose ∝ (Iλ²)^1/2 in intense lasers-solid interactions. Empirically, alignment with these predictions has been observed up to 3 x 10¹⁹ W/cm². Leveraging the OMEGA-EP short-pulse beam, we not only extended this scaling to 3 x 10²⁰ W/cm² but also produced unprecedented doses-4.7 and 5.4 rad in air at 1 m-for E_photon > 100 keV at 511 J and 972 J with a pulse duration of 0.5 ps and 5.8 ps, respectively. The efficiency of this process defies explanations based solely on operating at higher intensities. VPIC simulations, incorporating experimentally observed hotspots within the laser focus, unveiled stabilized propagation of the beam through 10s of microns pre-plasma. This stability, a balancing of self-focusing and density-induced defocusing, enhances the penetration of the overdense region through relativistic-induced-transparency (RIT), culminating in the acceleration of a larger volume of electrons.