Spontaneous emergence of non-planar electron orbits during direct laser acceleration by a linearly polarized laser pulse

Abstract

An electron irradiated by a linearly polarized relativistic intensity laser pulse in a cylindrical plasma channel can gain significant energy from the pulse. The laser electric and magnetic fields drive electron oscillations in a plane making it natural to expect the electron trajectory to be flat. We show that strong modulations of the relativistic γ-factor associated with the energy enhancement cause the free oscillations perpendicular to the plane of the driven motion to become unstable. As a consequence, out of plane displacements grow to become comparable to the amplitude of the driven oscillations and the electron trajectory becomes essentially three-dimensional, even if at an early stage of the acceleration it was flat. The development of the instability profoundly affects the x-ray emission, causing considerable divergence of the radiation perpendicular to the plane of the driven oscillations, while also reducing the overall emitted energy.

Scaling laws for direct laser acceleration in a radiation-reaction dominated regime

“…A rigorous analytical description of our setup requires a few simplifications. Similarly as in previous works, in this section we consider the laser to be a plane wave, and the channel fields to be a linear function of the distance from the propagation axis x [18,19,27]. Consequently, the channel fields are radially symmetric with respect to the x-axis.…”

“…This regime of electron acceleration is referred to as the direct laser acceleration (DLA) [7]. The rich physics of this setup has raised a keen interest among researchers in the past few years [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. It was reported that the efficiency of DLA may be enhanced using various strategies: parametric amplification of betatron oscillations [26][27][28][29], applying additional longitudinal electric field [30,31] or by "breaking of the adiabaticity that precludes electron energy retention" [32].…”

Beyond the ponderomotive limit: Direct laser acceleration of relativistic electrons in sub-critical plasmas

“…A parameter scan over the same range of a 0 and ω p0 /ω as in Fig. 11 reveals that there is a threshold for the amplification of the free transverse oscillations 24 . This threshold matches the energy enhancement threshold (dashed line in Fig.…”

“…We also address the role of electron injection into the laser beam and the limitations imposed by the super-luminosity of the laser field that is induced by the channel. This paper is based on a body of work performed by us over the last couple of years 14,[20][21][22][23][24] and is designed to serve in part as an overview of some novel aspects of the direct laser acceleration. Here we focus on illustrating the key qualitative concepts and phenomena, while providing references to those publications where one can find more detailed technical analysis.…”

Direct laser acceleration of electrons in the plasma bubble by tightly focused laser pulses

“…Since transverse laser wave fields are mainly responsible for DLA mechanism, DLA mechanism is analytically studied by approximating the laser pulse by a planar electromagnetic wave [19][20][21][22][23][24]. In this paper, we examine through an analytical theory and supporting PIC simulations the effect of a small but finite longitudinal electric field of the laser pulse in the DLA regime.…”