Micron-scale High Energy Density Matter Generated by Relativistic Laser-Solid Interactions*

Short-pulse, laser-solid interactions provide a unique platform for the generation and study of high-energy-density matter. Here, we present the first demonstration of near solid-density, micron-scale plasmas uniformly heated to keV temperatures. Experiments conducted using the relativistic 400 nm ALEPH laser at Colorado State University, front- and rear-side hard X-ray spectrometers were fielded to measure K-shell emission from thin copper and buried layer targets, enabling detailed diagnosis of second-harmonic laser heating of these materials. Spectral analysis of x-ray emission reveals uniform heating up to 3.0 keV over 1 μm depths. Collisional-radiative modelling and 3D collisional PIC simulations were in good agreement with experimental data on the depth and temperatures of these laser-produced plasmas. The significant bulk heating is attributed to MeV hot electrons that become trapped and undergo refluxing within the target sheath fields. These homogeneous, solid-density, multi-keV plasmas were used to examine ionization potential depression atomic models.