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Abstract
AbstractIt is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. Above this upper-limit critical power, the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force. Associated with the upper-limit power, a lower-limit critical plasma density is also found for a given laser spot size, below which self-focusing does not occur for any laser power. Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations. The present study provides new guidance for experimental designs, where self-guided propagation of lasers is essential.
Highlights
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]
There have been a lot of studies on this topic when the laser power is around Pc, e.g., laser channeling in underdense plasmas [16,17,18], laser guiding in plasma channels [19,20], and propagation of multi-laser beams in plasmas [21,22,23,24]
We have shown that there is an upper limit of the laser power Pu for self-focusing in plasma, which is a function of the initial spot size of the laser pulse and the plasma electron density
Summary
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]. It is shown that there is an upperlimit power for self-guided propagation of laser pulses in underdense plasma This is caused by the transverse ponderomotive force of the laser pulses, expelling local plasma electrons and creating an electron-free channel in a certain area. When the laser power is increased to 250 Pc = 10 Pu (219 TW) [Pu is an upperlimit power defined by Equation (13)], self-focusing does not appear, and the evolution of the laser pulse is very close to that in the vacuum, as observed in the first and third rows We call this phenomenon ponderomotive defocusing in a plasma. We will present a more detailed investigation by 2D PIC simulations and give a more detailed derivation of the upperlimit power
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