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

Abstract

We present an analytical theory that reveals the importance of the longitudinal laser electric field in the resonant acceleration of relativistic electrons by the tightly confined laser beam. It is shown that this field always counterworks to the laser transverse component and effectively decreases the final energy gain of electrons through direct laser acceleration mechanism. This effect is demonstrated by carrying out the particle-in-cell simulations in the setup where the wakefield in the plasma bubble is compensated by the longitudinal laser electric field experienced by the accelerated electrons. The derived scalings and estimates are in good agreement with numerical simulations.

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

“…If the predicted asymptotic I is much smaller for one of the limits (RR due to the laser or due to the channel fields), it means that this limit represents the dominant contribution to the radiation reaction. As it turns out, the I limit predicted by equation 24is frequently lower than the one predicted by equation (25). An example for a 0 = 500 is given in figure 4.…”

“…Analytical predictions of the maximum electron energy as a function of channel density and electron initial radial position are provided by equations (9) and (21) using radiation-reaction reduced value of I given by the lowest estimate from equations (24) and (25). The required acceleration distance to achieve this energy can be estimated through equation (13).…”

“…Both equations (24) and (25) predict an asymptotic value that particles with a large initial value of I 0 would tend to after a resonant cycle. If the predicted asymptotic I is much smaller for one of the limits (RR due to the laser or due to the channel fields), it means that this limit represents the dominant contribution to the radiation reaction.…”

“…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].…”

Two-Pulse Direct Laser Acceleration in a Laser-Driven Plasma Accelerator

“…In these studies, DLA was controlled by increasing the pulse length of the drive pulse, thereby increasing the amplitude of the pulse tail that interacted with the accelerating electron bunch. This experimental study is based on existing simulation and theory [20,21,22,23]. We seek to make the DLA process more controllable by using a second independent pulse to control electrons in a wake driven by the first pulse.…”