We present experimental results on fast-electron energy deposition into solid targets in ultrahigh intensity laser-matter interaction. X-ray $K\alpha$ emission spectroscopy with absolute photon counting served to diagnose fast-electron propagation in multilayered targets. Target heating was measured from ionization-shifted $K\alpha$ emission. Data show a $200\mathrm{\mu }\mathrm{m}$ fast-electron range in solid Al. The relative intensities of spectrally shifted $\mathrm{Al}K\alpha$ lines imply a mean temperature of a few tens of eV up to a $100\mathrm{\mu }\mathrm{m}$ 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.

• Received 9 May 2005

DOI:https://doi.org/10.1103/PhysRevE.73.046402