Spatiotemporal Evolution of Radiation Structures in Nonlinear Thomson Scattering as a Function of Laser Pulse Width

This study investigates the spatiotemporal evolution of nonlinear Thomson radiation from an electron driven by a tightly focused circularly polarized Gaussian laser pulse in the presence of a uniform externally applied magnetic field. The laser pulse width L is treated as the control parameter of independent simulations and is scanned with sufficiently fine resolution to identify dynamical transitions that may be obscured by sparse parameter sampling. The temporal radiation sequence, electron dynamics, optimal radiation direction, and full angular distribution are analyzed within a unified framework. The results reveal that the maximum radiated power per unit solid angle exhibits a distinct plateau–transition–plateau evolution rather than a smooth dependence on pulse width. Comparisons with percentile-based, time-averaged, and time-integrated radiation quantities confirm that this step effect is not solely an artifact of global maximization, but originates from the intermittent preservation and renewal of record radiation peaks. The strongest radiation events are governed by the combined contributions of the acceleration-dependent numerator and the high-order directional factor ξ−6, with the latter providing the dominant amplification of favorable emission geometries. As L increases, the optimal radiation polar angle shifts toward smaller values, indicating enhanced collimation, while the full angular radiation structure exhibits continuous azimuthal rotation and hierarchical relay activation from larger to smaller polar angles. These results establish a coherent physical picture of the spatiotemporal evolution of nonlinear Thomson radiation as a function of laser pulse width and provide source-side guidance for controlling compact high-frequency radiation with potential relevance to X-ray diffraction, scattering, and the high-resolution characterization of crystalline materials.