Study of ultraintense laser propagation in overdense plasmas for fast ignition

Abstract

Laser plasma interactions in a relativistic regime relevant to the fast ignition in inertial confinement fusion have been investigated. Ultraintense laser propagation in preformed plasmas and hot electron generation are studied. The experiments are performed using a 100 TW 0.6 ps laser and a 20 TW 0.6 ps laser synchronized by a long pulse laser. In the study, a self-focused ultraintense laser beam propagates along its axis into an overdense plasma with peak density 10 22 / cm 3 . Channel formation in the plasma is observed. The laser transmission in the overdense plasma depends on the position of its focus and can take place in plasmas with peak densities as high as 5 ϫ 10 22 / cm 3 . The hot electron beams produced by the laser-plasma interaction have a divergence angle of ϳ30°, which is smaller than that from laser-solid interactions. For deeper penetration of the laser light into the plasma, the use of multiple short pulse lasers is proposed. The latter scheme is investigated using particle-in-cell simulation. It is found that when the pulse duration and the interval between the pulses are appropriate, the laser pulse train can channel into the plasma deeper than a single longer pulse laser of similar peak intensity and total energy.

Relativistic critical density increase and relaxation and high-power pulse propagation

“…In 2D and 3D cases, the relativistic self focusing 6,7 and the filamentation 19 are also expected to play an important role in the relativistic laser pulse propagation. For instance, it has been observed that the laser propagation can be enhanced by the relativistic self focusing.…”

“…For instance, it has been observed that the laser propagation can be enhanced by the relativistic self focusing. 6,7 While in the case of laser interaction with a thin plasma layer, pulse shaping, plasma expansion and heating will considerably affect the laser propagation. [26][27][28] Simulation using mobile ions has shown that the laser intensity threshold for inducing the relativistic transparency will be increased significantly.…”

“…High-power laser pulse penetration into relativistically transparent plasmas 1,2 at intensity larger than 10 18 Wcm À2 is of great relevance in laser plasma particle acceleration, 3,4 fast ignition, [5][6][7][8] laser pulse tailoring. 9,10 In particular, an increase of the critical density n c makes the fast particle transport and heat losses more easily to be controlled in laser plasma interactions, [11][12][13][14] and it provides a higher, more favourable laser energy coupling to the compressed core in fast ignition schemes.…”

Relativistic Propagation of Linearly/Circularly Polarized Laser Radiation in Plasmas

“…The dependence of the electron mass on intensity causes significant change of characteristic properties of the plasma and its nonlinear processes; the increase in effective electron mass decreases the electron plasma frequency and makes the penetration of electromagnetic waves into the overdense area of plasma, which is known as self-induced transparency or electromagnetically induced transparency, and is the cause of relativistic self-focusing. A combination of the relativistic self-focusing and relativistic induced transparency enables transmission of laser energy deep into plasmas which is useful for fast ignition of inertial fusion [2]. This so-called penetration sensitively depends on the focal position of the laser intensity due to the inhomogeneous density profile of the plasma and convergence of the laser pulse by final focusing optics.…”

Upper-limit power for self-guided propagation of intense lasers in underdense plasma

“…Laser propagation in plasma is a fundamental and important issue in laser plasma interactions, which is related to a number of applications such as the fast ignition scheme for inertial confinement fusion [1,2] , the laser wakefield acceleration of electrons [3][4][5][6][7][8] , and lightning channeling in air [9,10] . Usually, these applications require that intense laser pulses can stably propagate over a large distance in plasma.…”