Radiation-Reaction-Force-Induced Nonlinear Mixing of Raman Sidebands of an Ultraintense Laser Pulse in a Plasma

Abstract

Stimulated Raman scattering of an ultraintense laser pulse in plasmas is studied by perturbatively including the leading order term of the Landau-Lifshitz radiation reaction force in the equation of motion for plasma electrons. In this approximation, the radiation reaction force causes a phase shift in nonlinear current densities that drive the two Raman sidebands (anti-Stokes and Stokes waves), manifesting itself into the nonlinear mixing of two sidebands. This mixing results in a strong enhancement in the growth of the forward Raman scattering instability.

Electronic parametric instabilities of an ultrarelativistic laser pulse in a plasma

“…In this paper, we extend the results of Ref. [16] and show that the RR force not only influences the properties of the unstable modes associated with the Raman and modulational instabilities, but also changes the nature of the unstable perturbation in the ultra-relativistic regime of laser-plasma interaction.…”

“…The details in deriving the dispersion relation can be found in Ref. [16]. We briefly recall here the key points for the sake of continuity; a circularly polarized (CP) pump laser of strength a 0 = eA 0 /m e c 2 , A 0 is the vector potential of the laser, e is the electronic charge, m e is the electron mass, and c is the velocity of light in vacuum, propagates in an infinite plasma with uniform plasma electron density n 0 .…”

“…[16], the effect of radiation reaction force on the equilibrium propagation was analyzed in the limit a 0 ≤ a rad , approximating p ⊥ as p ⊥ = m e ca 0 (1 − iεγ 0 |a 0 | 2 ), where ε = 2πr e /3λ 0 = 7.38 × 10 −9 , and γ 0 = (1 + a 2 0 /2) 1/2 . This equilibrium propagation yields a dispersion relation of the form, ω 2 0 = k 2 0 c 2 + ω 2 p 1 − iµ|A 0 | 2 γ 0 /2 , where ω 2 p = ω 2 p /γ 0 , ω p = (4πn 0 e 2 /m e ) 1/2 , and µ = 2e 4 ω 0 /3m 3 e c 7 , depicting the damping due to the radiation reaction force [16]; see also [21]. It can be noted that µ accounts for the radiation reaction induced phase shift and is inversely proportional to the cube power of the electron mass.…”

“…As plasma is a self-organising system, it can support a multitude of modes related to wave propagation. Some of these modes can benefit from the radiation damping of an electromagnetic wave in plasmas and lead to novel effects [16].…”

“…It is instructive to examine the role of the radiationreaction (RR) force on the plasma dynamics in the ultrarelativistic regime of the laser-plasma interaction, which has been an active area of research in the last few years, especially with regards to the developments of QED-PIC codes [17][18][19]. In light of this, the effect of the RR force was included in the formalism of electronic parametric instabilities [16]. This formalism is valid in a classical electrodynamics regime where quantum effects arising due to photon recoil and spin effects are negligible [15].…”