Exotic Dense-Matter States Pumped by a Relativistic Laser Plasma in the Radiation-Dominated Regime

In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of $KK$ hollow atoms (atoms without $n=1$ electrons) from thin Al foils was observed at pulse intensities of 3×10²⁰ W/cm². The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the $KK$ hollow atom production. We estimate that this x-ray field has an intensity of >5×10¹⁸ W/cm² and is in the 3 keV range.