Fuchset al.Reply:

Experimental study of laser penetration in overdense plasmas at relativistic intensities. I: Hole boring through preformed plasmas layers

“…Indeed, we previously observed that such long underdense gradients with gradient-scale length around 100-200 m are favorable conditions for the beam channeling and self-focusing with beam intensity gain up to a factor of 10. 32 Moreover, when the tail of the target is at higher underdense densities, as it is the case for the denser targets, these effects are enhanced and the beam intensity enhancement increases. 31 This model also shows, for very overdense layers, a very sharp increase of the transmission, similar to the experimental trend, as we vary the beam intensity at fixed plasma parameters, as shown in Fig.…”

“…1. 32 Thus we can fit the electron density profiles obtained from a 1D Lagrangian hydrocode ͑CHIVAS͒ 40 to the measured underdense density profiles and infer the overdense plasma parameters: The peak density n max /n c and the thickness at critical density l c . The use of 1D geometry is justified as the plasma-creating beam focal spot is very large ͑400 m͒ compared to the longitudinal size of the plasma given roughly by c s ϳ70 m at T e ϳ300 eV, according to the hydrodynamic simulation ͑ is the duration of the plasma-creating beam͒.…”

“…[2][3][4][5][6][7] Recently, this interest has been considerably intensified, both theoretically [8][9][10][11][12][13][14][15][16] and experimentally, [17][18][19][20][21][22][23] due to the availability of lasers capable of delivering intensities above 10 19 W•cm Ϫ2 , 24 and to the development of the fast ignitor ͑FI͒ concept 25,26 which should allow higher fusion gains and relaxed constraints for inertial confinement fusion ͑ICF͒. a͒ Electronic mail: julien@greco2.polytechnique.fr In this scheme, after having channeled through the underdense corona, [27][28][29][30][31][32] intense short pulses have to heat, via the fast electrons generated, an incompletely compressed thermonuclear target. Thus, external ignition could be achieved.…”

Additional focusing of a high-intensity laser beam in a plasma with a density ramp and a magnetic field

“…Therefore, selffocusing of a high-intensity laser beam in a plasma is a very important research issue nowadays. [8][9][10][11][12][13][14] The experimental results on relativistic self-focusing in hydrogen gas have been reported by Fedosejevs et al 15 Hafizi et al 16 studied the propagation of an intense laser beam in a plasma, including the relativistic and ponderomotive effects. Their results show that the laser beam can acquire a minimum spot size due to the relativistic self-focusing in a plasma.…”

Experimental study of laser penetration in overdense plasmas at relativistic intensities. II: Explosion of thin foils by laser driven fast electrons

“…The time-coincidence between this beam and the interaction beam has been monitored in another experiment where we studied the expansion of underdense density channels on the time scale of a few picoseconds. 37 The fringes are located in a small zone ͑ϳ20 m in diameter͒ on the rear side of the thick target. They indicate the presence of an expanding plasma on the rear side of the target that is not reached by the laser pulse.…”