Fast-electron transport and heating of solid targets in high-intensity laser interactions measured by Kα fluorescence

We present experimental results on fast-electron energy deposition into solid targets in ultrahigh intensity laser-matter interaction. X-ray Kα emission spectroscopy with absolute photon counting served to diagnose fast-electron propagation in multilayered targets. Target heating was measured from ionization-shifted Kα emission. Data show a 200 μm fast-electron range in solid Al. The relative intensities of spectrally shifted Al Kα lines imply a mean temperature of a few tens of eV up to a 100 μm depth. Experimental results suggest refluxing of the electron beam at target rear side. They were compared with the predictions of both a collisional Monte Carlo and a collisional-electromagnetic, particle-fluid transport code. The validity of the code modeling of heating in such highly transient conditions is discussed.