Damping dynamics of the centroid oscillation of a relativistic laser pulse in a plasma channel

TL;DR

This paper investigates the damping mechanisms of laser pulse centroid oscillations in plasma channels, combining theoretical models and 3D simulations to understand effects in both non-relativistic and relativistic regimes.

Contribution

It introduces an analytical model for oscillation decay and reveals relativistic effects causing rapid damping, advancing understanding of laser-plasma interactions in wakefield accelerators.

Findings

Decay in centroid oscillation due to mode leakage and walk-off in non-relativistic pulses.

Relativistic pulses develop axial chirp leading to phase mixing and rapid damping.

Model validation through particle-in-cell simulations.

Abstract

The centroid oscillation of an offset laser pulse propagating in a preformed plasma channel is investigated through theoretical analysis and three-dimensional particle-in-cell simulations. For non-relativistic laser pulses, the mode leakage of a finite channel and the temporal walk-off between the fundamental and high order modes of a finite-duration laser induce a decay in the laser centroid oscillation. An analytical model characterizing these decay mechanisms is derived and validated by simulations. For relativistic laser pulses, the slice-based centroid oscillation frequency develops an axial chirp due to relativistic channel modification and photon deceleration. This chirp leads to phase mixing across different axial slices of the pulse, resulting in a rapid damping of the overall centroid oscillation. Understanding this oscillation damping is crucial for mitigating electron beam pointing jitter and maintaining beam quality in high-energy, channel-guided laser wakefield accelerators.