The interaction of short and intense laser pulses with plasmas is a very efficient source of relativistic electrons with tunable properties. In low-density plasmas, we observed bunches of electrons up to 200 MeV, accelerated in the wakefield of the laser pulse. Less energetic electrons (tens of megaelectronvolt) have been obtained, albeit with a higher efficiency, during the interaction with a pre-exploded foil or a solid target. When these relativistic electrons slow down in a thick tungsten target, they emit very energetic Bremsstrahlung photons which have been diagnosed directly with photoconductors, and indirectly through photonuclear activation measurements. Dose, photoactivation, and photofission measurements are reported. These results are in reasonable agreement, over three orders of magnitude, with a model built on laser–plasma interaction and electron transport numerical simulations.

We present experimental and numerical results on the propagation and energy deposition of laser-generated fast electrons into conical targets. The first part reports on experimental measurements performed in various configurations in order to assess the predicted benefit of conical targets over standard planar ones. For the conditions investigated here, the fast electron-induced heating is found to be much weaker in cone-guided targets irradiated at a laser wavelength of 1.057 mu m, whereas frequency doubling of the laser pulse permits us to bridge the disparity between conical and planar targets. This result underscores the prejudicial role of the prepulse-generated plasma, whose confinement is enhanced in conical geometry. The second part is mostly devoted to the particle-in-cell modeling of the laser-cone interaction. In qualitative agreement with the experimental data, the calculations show that the presence of a large preplasma leads to a significant decrease in the fast electron density and energy flux near the target rear side. (c) 2008 American Institute of Physics

The version of Fig. 4 that was inadvertently included in the original publication did not show the results of Monte Carlo modeling referred to in the caption and the text. The correct figure and its caption are shown below. This does not affect the conclusions of the article. FIG. 4. Integrated K ␣ fluorescence energy versus mass fraction of Cu fluor in Al/ Cu/ Al targets. The front Al layer varied from zero to 500 m, the Cu layer was 20-25 m. The back Al layer was 100 m for the four ϫ points, and 40 m for the ϩ, 10-20 m otherwise. The open symbols show the predictions from Monte Carlo modeling with an arbitrary relative normalization. The back Al layer in the model is either 16 m ͑square͒ or 100 m ͑triangle͒.

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