Wavefront distortion and compensation of weakly relativistic vortex beams propagating in plasmas

Abstract

The propagation of electromagnetic waves in plasmas is one of the longstanding concerns in the field of laser plasma. It is closely related to research on radiation source generation, particle acceleration, and inertial confinement fusion. Recently, the proposal of various schemes for generating intense vortex beams has led to an increasing number of researchers focusing on the interaction between intense vortex beams and plasmas. This has resulted in significant progress in various areas of research, including particle acceleration, high-order harmonic generation, quasi-static self-generated magnetic fields, and parametric instability. Unlike traditional Gaussian beams, vortex beams, characterized by their hollow amplitude and helical phase, can exhibit new phenomena when propagating through plasmas. In this paper, we primarily focus on studying the influence of the propagation process on the wave structure of vortex beams before filamentation occurs. Based on three-dimensional particle-in-cell simulations, we find that weakly relativistic vortex beams exhibit wavefront distortion during their propagation in plasmas. The degree of this distortion is closely related to the intensity of the electromagnetic wave and the propagation distance for a given plasma density. Theoretical explanations for this phenomenon are provided through a phase correction model, taking into account the relativistic mass correction of electrons. Besides, we demonstrates that the wavefront distortion can be compensated and suppressed by appropriately modulating the initial plasma density, as confirmed through three-dimensional particle simulations. The results of decomposing the wavefront into Laguerre-Gaussian (LG) mode components indicate that the wavefront distortion is primarily induced by high-order p LG modes, and it is independent of other l LG modes. Additionally, we extend our investigation to the propagation of vortex beam in axially magnetized plasmas, where the phase correction model can also effectively explain the occurrence of wavefront distortion. Our work deepens our understanding of the interaction between intense vortex beams and plasmas, providing valuable insights for the design of plasma devices intended for the manipulation of intense vortex beams in future research.