Generation of MeV electrons and positrons with femtosecond pulses from a table-top laser system

In experiments, the feasibility was demonstrated of generating multi-MeV electrons in a form of a collimated beam utilizing a table-top laser system delivering 200 fs pulses with P-L=1.2 TW and 10 Hz capability. The method uses the process of relativistic self-channeling in a high-density gas jet producing electron densities in the range of 3x10(19)-6x10(20) cm(-3). In a thorough investigation, angularly resolved and absolutely calibrated electron spectra were measured and their dependence on the plasma density, laser intensity, and gas medium was studied. For the optimum electron density of n(e)=2x10(20) cm(-3) the effective temperature of the electron energy distribution and the channel length exhibit a maximum of 5 MeV and 400 mum respectively. The laser-energy to-MeV-electron efficiency is estimated to be 5%. In a second step, utilizing the multi-MeV electron beam anti-particles, namely positrons, were successfully generated in a 2 mm Pb converter. The average intensity of this new source of positrons is estimated to be equivalent to a radioactivity of 2x10(8) Bq and it exhibits a very favorable scaling for higher laser intensities. (C) 2002 American Institute of Physics