91̽»¨

Abstract:

The study of fast electrons generated in laser-matter interactions and their transport through matter is of great interest for the fast ignition concept in the inertial confinement fusion. A typical experimental approach is the interaction of intense laser radiation with foil targets. The transport of the electrons through the foil can be studied with several techniques including X-ray emission measurements and direct measurements on electrons leaving the foil. Some laser-matter interaction features can be monitored using spectroscopy in the visible range. Here we will focus our attention on some of the experimental techniques that have been used in laser-foil experiments at ILIL laboratory in Pisa and in a VULCAN Petawatt experiment at RAL. In particular we will describe high resolution X-ray spectroscopy with a bent crystal, K-alpha flux measurements, direct measurements of the angular distribution and spectrum of the electrons, and spectroscopy of the 3/2ω and 2ω harmonics of the laser radiation.

Abstract:

During the last few years laser-driven plasma accelerators have been shown to generate quasi-monoenergetic electron beams with energies up to several hundred MeV. Extending the output energy of laser-driven plasma accelerators to the GeV range requires operation at plasma densities an order of magnitude lower, i.e. 10(18) cm(-3), and increasing the distance over which acceleration is maintained from a few millimetres to a few tens of millimetres. One approach for achieving this is to guide the driving laser pulse in the plasma channel formed in a gas-filled capillary discharge waveguide. We present transverse interferometric measurements of the evolution of the plasma channel formed and compare these measurements with models of the capillary discharge. We describe in detail experiments performed at Lawrence Berkeley National Laboratory and at Rutherford Appleton Laboratory in which plasma accelerators were driven within this type of waveguide to generate quasi-monoenergetic electron beams with energies up to I GeV.

Abstract:

The first evidence of x-ray harmonic radiation extending to 3.3, 3.8 keV (order n>3200) from petawatt class laser-solid interactions is presented, exhibiting relativistic limit efficiency scaling (η∼n-2.5-n-3) at multi-keV energies. This scaling holds up to a maximum order, nRO∼81/2γ3, where γ is the relativistic Lorentz factor, above which the first evidence of an intensity dependent efficiency rollover is observed. The coherent nature of the generated harmonics is demonstrated by the highly directional beamed emission, which for photon energy hν>1keV is found to be into a cone angle ∼4°, significantly less than that of the incident laser cone (20°). © 2007 The American Physical Society.