Xue-Ren Hong et al. [EPL, 139 (2022) 14001] Details of the electron dynamics and Thomson backscattering of electrons moving in a combined field of a tightly focused Gaussian laser pulse and an external uniform magnetic field are investigated. It is found that electrons can be pushed out from the laser pulse by a qualitative dynamic, leading to the phenomenon that the symmetry of the electron dynamics from the Gaussian envelope is broken. In this comment, we investigate the motion law of electrons under precise laser pulses, and we find that the longitudinal vector potential of electrons has a non-negligible effect on the electron motion, especially when the laser peak amplitude is enhanced, the laser pulse width becomes wider, the beam waist of the laser pulse becomes tighter. In addition, we explain the reason for such a large effect of the longitudinal vector potential from the point of view of electron dynamics.

This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron’s initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum’s harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings, when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.

Influence of acceleration of electron on relativistic nonlinear Thomson scattering in tightly focused linearly polarized laser pulses is investigated for the first time. In the framework of classical electrodynamics, it is deduced and found that the more severe the change of the electron transverse acceleration, the stronger the asymmetry of the radiation angle distribution and the greater the transverse acceleration, the greater the radiation energy. Tightly focused, ultrashort, and high-intensity lasers lead to violent electron acceleration processes, resulting in a bifurcated radiation structure with asymmetry and higher energy. Additionally, the change of the initial phase of the laser brings about the periodic change of the acceleration, which in turn makes the radiation change periodically with the initial phase. In other cases, the radiation is in a symmetrical double-peak structure. These phenomena will help us to modulate radiation with more energy collimation.

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Hong et al. [Phys. Plasmas 29, 043102 (2022)] researched the nonlinear Thomson backscatter in a highly focused Gaussian linear laser pulse. They studied the law of backward harmonic spectrum and electron motion trajectory and put forward the view that “the electron will be pushed to the −z-axis by the responsible force of the falling edge of the laser pulse when the interaction time is long enough.” In this Comment, we study the electron motion law under the precise laser pulse expression. We find and explain that the initial position of the electron is the reason why the electron is pushed to the −z-axis. Only when the initial position of the electron is in the −z half-axis, the electron will be pushed away at the end of the pulse.