SUPRATHERMAL AND RELATIVISTIC ELECTRONS PRODUCED IN LASER-PLASMA INTERACTION AT 0.26, 0.53, AND 1.05-MU-M LASER WAVELENGTH

Very energetic electrons produced in laser-plasma interactions at 0.26, 0.53, and 1.05-mu-m laser wavelength have been measured. The targets were 1.5-mu-m plastic foils and the laser intensity was around 10(15) W/cm2. Detailed measurements of the electron distribution performed at a 0. 26-mu-m laser wavelength exhibit an angular distribution strongly peaked along the laser axis at the highest energies (above 200 keV). Electrons up to 1.3 MeV have been observed in the 1.05-mu-m experiments. The hot temperatures inferred from the measured energy distributions are of the order of 100 keV in the 1.05-mu-m experiments, and 50 keV in the 0.53-mu-m/0.26-mu-m experiments. The experimental electron emission features are discussed with a special focus on the relation between the linear as well as the nonlinear electron plasma wave generation mechanisms and the maximum energy reached by an electron trapped in this wave.