Generation of ultra-short light pulses by a rapidly ionizing thin foil
  A thin and dense plasma layer is created when a sufficiently strong laser pulse impinges on a solid target. The nonlinearity introduced by the time-dependent electron density leads to the generation of harmonics. The pulse duration of the harmonic radiation is related to the risetime of the electron density and thus can be affected by the shape of the incident pulse and its peak field strength. Results are presented from numerical particle-in-cell-simulations of an intense laser pulse interacting with a thin foil target. An analytical model which shows how the harmonics are created is introduced. The proposed scheme might be a promising way towards the generation of attosecond pulses.   PACS number(s): 52.40.Nk, 52.50.Jm, 52.65.Rr 
D. Bauer, R.R.E. Salomaa (Helsinki University of Technology, Finland),   and P. Mulser (TQE, Darmstadt University of Technol...