Introduction to ultra-intense-laser plasma interactions
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A brief introduction to the interaction of ultra‐intense laser pulses with plasmas is presented. A number of interesting phenomena due to relativistic electron dynamics are reviewed in simple calculations. These relativistic effects range from nonlinear frequency shifts of light waves to penetration of overdense plasmas, filamentation and self‐focusing. Finally, computer simulations are used to illustrate several strongly nonlinear effects in such plasmas, including heating by the oscillating ponderomotive force and relativistic filamentation.Keywords:
Filamentation
Relativistic plasma
Ponderomotive force
Self-focusing
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The influence of ponderomotive force-induced plasma motion on filamentation is examined, using both linear and non-linear descriptions. Although the time asymptote of the process is identical to the stationary convective amplification of filaments, the dynamics of the plasma response may have a serious impact on the transient behaviour of filamentation. The plasma motion contains large amplitude oscillations of inhomogeneities in the laser beam with maxima that substantially exceed the asymptotic value and temporary growth of the very narrow filaments, which cannot be amplified in the stationary approximation.
Filamentation
Ponderomotive force
Asymptote
Self-focusing
Dynamics
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The interaction between an ultra-short ultra-intense laser pulse and a solid target with a low density pre-plasma is examined. Both linear and circular polarizations of the laser are considered. The electrons in the pre-plasma are accelerated by the ponderomotive force of propagating laser pulse, and the dependences of the maximum electron energy on the laser intensity and the pre-plasma density are examined. The target electrons are accelerated by J×B mechanism, and the maximum energy achieved is much lower than that of the pre-plasma electrons. In this sense, the pre-plasma is advantageous for energetic electrons generation in the ultra-short ultra-intense laser-solid interaction.
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Self-focusing a laser beam in collisional plasma is investigated under the weak relativistic-ponderomotive nonlinearity. In this case, the plasma equilibrium density is modified and it causes generation of the nonlinearity due to the Ohmic heating of electrons, collisions, and the weak relativistic-ponderomotive force during the interaction of the laser beam with the plasma. Our theoretical and simulation results show that a significant nonlinearity in laser self-focusing can occur under the weak relativistic-ponderomotive regime for some appropriate simulation parameters.
Ponderomotive force
Self-focusing
Relativistic plasma
Relativistic electron beam
Relativistic quantum chemistry
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This paper presents an investigation into the behavior of a laser beam of finite diameter in plasma with respect to forces and optical properties, which lead to self-focusing of the beam. The transient setting of ponderomotive nonlinearity in a collisionless plasma has been studied, and consequently the self-focusing of the pulse, and the focusing of the plasma wave occurs. The description of a self-focusing mechanism of laser radiation in the plasma due to nonlinear forces acting on the plasma in the lateral direction, relative to the laser has been investigated in the nonrelativistic regime. The behavior of the laser beams in plasma, which is the domain of self-focusing at high or moderate intensity, is dominated by the nonlinear force. The investigation of self-focusing processes of laser beams in plasma results from the relativistic mass and energy dependency of the refractive index at high laser intensities. Here, the relativistic effects are considered to evaluate the relativistic self-focusing lengths for the Nd glass radiation, at different plasma densities of various laser intensities. A numerical program in c ++ that incorporates both the ponderomotive force in self-focusing mechanism and relativistic effects has been developed to explore in depth self-focusing over a wide range of parameters.
Self-focusing
Ponderomotive force
Relativistic plasma
Thermal blooming
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The onset of laser beam filamentation in a preformed nonuniform plasma is investigated by using a two-dimensional computer code in which time-dependent plasma hydrodynamics and heat transport effects are accounted for. Laser beam propagation is modeled using a paraxial wave approximation—refraction, diffraction, absorption, and ponderomotive force effects are accounted for. The simulations reveal details by which multifilamentary plasma and laser beam structures evolve in the region near the critical density surface. For the particular case of a 1.05 μm laser beam with an intensity of 1015 W/cm2 incident on a long scale length preformed plasma, a consistent treatment of the ponderomotive forces and of the plasma dynamics is found to be essential in determining the evolution of the filamentary structures.
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Ponderomotive force
Self-focusing
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Many practical applications of ultrashort, high power laser pulses require the laser pulse to be focused to a high intensity and remain relatively collimated over large distances in plasmas. Such applications include x-ray lasers [1], laser-plasma-based electron accelerators [2] and laser-induced nuclear fusion schemes [3]. Self-focusing and self-channeling of laser pulses by relativistic and ponderomotive mechanisms [4] are laser-plasma processes which can accomplish this feat.
Collimated light
Ponderomotive force
Self-focusing
Ultrashort pulse laser
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Production of protons with energies of $\ensuremath{\sim}20\mathrm{keV}$ have been observed to originate from the interaction of a high intensity laser with a preformed underdense plasma. The energy and distribution of ions are explained by acceleration by the ponderomotive force resulting from filamentation.
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Ponderomotive force
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Filamentation of a circularly polarized short pulse laser propagating along the direction of ambient magnetic field in plasma is studied. The nonlinearity arises through the combined effect of relativistic mass variation and ponderomotive force induced electron cavitation. The growth rate is maximum Γmax for an optimum filament size, qopt−1. Γmax and qopt increases with plasma density and ambient magnetic field.
Filamentation
Ponderomotive force
Relativistic plasma
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In this paper we study the influence of the magnetised thermal conductivity on the propagation of a nanosecond $10^{14} \mathrm{Wcm}^{-2}$ laser in an underdense plasma by performing simulations of a paraxial model laser in a plasma with the full Braginskii magnetised transport coefficients. Analytic theory and simulations show the shortening of the self-focal length of a laser beam in a plasma as a result of the reduction of the plasma thermal conductivity in a magnetic field. Furthermore the filamentation of a laser via the thermal mechanism is found to have an increased spatial growth rate in a magnetised plasma. We discuss the effect of these results on recent magnetised inertial fusion experiments where filamentation can be detrimental to laser propagation and uniform laser heating. We conclude the application of external magnetic fields to laser-plasma experiments requires the inclusion of the extended electron transport terms in simulations of laser propagation.
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Self-focusing
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The filamentation of ultrashort laser pulses (shorter than a plasma period) propagating in tenuous plasmas is studied. In this regime relativistic and ponderomotive nonlinearities tend to cancel each other. Time-dependent residual nonlinear plasma response brings about the dynamical filamentation with the maximum unstable transverse wave number decreasing in the course of laser pulse propagation. Dynamics of a hot spot that seeds the filamentation instability is studied numerically and reveals a good agreement with the analytical results.
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