Ultra-intense laser pulse propagation in plasmas: from classic hole-boring to incomplete hole-boring with relativistic transparency

Abstract

Relativistic laser pulse propagation into homogeneous plasmas has been investigated as a function of plasma density. At first, the propagation features are compared systematically between relativistic transparency (RT) and hole-boring (HB). Paramountly, a considerably broad intermediate regime, namely the incomplete HB regime, has been found between the RT regime and the HB regime for an extremely intense circularly polarized (CP) pulse. In this regime HB proceeds in collaboration with RT, resulting in a much faster propagation speed and a higher cut-off energy of fast ions than in the classic HB regime. Similarly to the classic HB regime, formulae are presented to model the laser propagation and the ion acceleration according to the modified momentum flux balance in this incomplete HB regime. The simulations give the density boundary between this incomplete HB regime and the classic HB regime for CP pulses, which is crucial for estimating the maximum mean ion energy and the maximum conversion efficiency that can be achieved by the classic HB acceleration at a given laser intensity. For linear polarization (LP) the propagation mechanism apparently undergoes a transition in time between these two regimes. A detailed comparison between LP and circular polarization is made for these phenomena.

Synchrotron radiation, pair production, and longitudinal electron motion during 10-100 PW laser solid interactions

“…This is a demonstration of the decoupling of ions and electrons observed as a critical part of the RESE mechanism in Brady et al 4 and is the same mechanism as the change from conventional to incomplete hole boring in Weng 17 . Between these two extremes is a region ( figure 12 c) where ions are important to the motion of the electrostatic front but even in the absence of ion motion the front still propagates.…”

Collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near critical density plasmas

“…This is because at this moment the laser front propagates at a speed as fast as 0.27c, so does the charge-separation field. As a result, the ion kinetic energy in the co-moving frame of the charge-separation field is about m i v 2 laser /2 ≃ 80m e c 2 , which is much larger than the peak of electrostatic potential Φ max ≃ 2.5m e c 2 at this moment as shown in However, the forward velocity of the laser front will gradually decrease due to the accumulation of particles ahead of the laser front and the dissipation of laser pulse in a dense plasma 27,32 . As the ponderomotive force of a linearly polarized pulse is time oscillating, it cannot compress a tenuous plasma immediately if a > n e /n c .…”

“…This is because an ultra-intense laser pulse will propagate too fast in a near critical density plasma due to the strong relativistic transparency 27 , so there's no enough time for the electrons and ions to accumulate sufficiently ahead of the laser front.…”

“…In the interaction of an intense laser pulse with a highly overdense target, the shock speed is mainly determined by the laser hole-boring (or piston) velocity v HB ≃ I/m i n i c 312, 15 . While laser-driven collisionless shock has been extensively studied using highly overdense targets [11][12][13][14][15][18][19][20] , the laser-plasma interactions are more complicated in the near critical density regime 27,28 and the collisionless shocks excited therein are rather unexplored 29 .…”

Mitigating the hosing instability in relativistic laser-plasma interactions

“…In this application of hole-boring [30][31][32][33], a high-power laser pulse is propagated into the coronal plasma between the compression and ignition pulses to create a low-density channel as far into the critical region as possible, thus minimizing the distance the ignition-stage fast electrons have to travel, and in so doing, minimizing the cross-sectional area of the beam upon reaching the compressed target and maximizing the delivered energy flux [34][35][36]. One of the major difficulties present in hole-boring is the hosing instability which introduces perturbations to the pulse's propagation, ultimately leading to strong tilting in the channel's direction [37][38][39][40].…”