OBSERVATION OF THE PLASMA CHANNEL DYNAMICS AND COULOMB EXPLOSION IN THE INTERACTION OF A HIGH-INTENSITY LASER-PULSE WITH A HE GAS-JET

We report the first interferometric observations of the dynamics of el ectron-ion cavitation of relativistically self-focused intense 4 TW, 4 00 fs laser pulse in a He gas jet. The electron density in a channel 1 mm long and 30 mu m in diameter drops by a factor of approximately 10 from the maximum value of similar to 8 x 10(19) cm(-3). A high radial velocity of the plasma expansion, similar to 3.8 x 10(8) cm/s, corres ponding to an ion energy of about 300 keV, is observed. The total ener gy of fast ions is estimated to be 6% of the laser pulse energy. The h igh-velocity radial plasma expulsion is explained by a charge separati on due to the strong ponderomotive force. This experiment demonstrates a new possibility for direct transmission of a significant portion of the energy of a laser pulse to ions. (C) 1997 American Institute of P hysics. [S0021-3640(97)00824-4].