Synergistic Modulation of Nonlinear Thomson Scattering Radiation in a Cross-Collision Geometry by Laser Amplitude and Initial Electron Energy

Relativistic nonlinear Thomson scattering (RNTS) provides an effective route for generating ultrashort and high-frequency radiation. Its radiation characteristics are determined not only by the laser field strength, represented by the laser amplitude a0 (the normalized laser amplitude), but also by the initial electron energy, expressed by γ0 (the initial Lorentz factor). To further clarify the coupled effects of a0 and γ0 in a cross-collision geometry, this study employs a tightly focused circularly polarized Gaussian laser field model including high-order nonparaxial corrections, and investigates the variations in electron dynamics and radiation behavior under different laser amplitudes a0 and initial Lorentz factors γ0. The numerical results show that increasing a0 enhances the nonlinear oscillation and instantaneous acceleration of the electron in the laser field, thereby increasing the radiation intensity and promoting spectral extension toward higher-frequency regions. In contrast, increasing γ0 strengthens the relativistic inertia of the electron, making its motion more directional and further affecting the angular distribution and temporal compression characteristics of the emitted radiation. The combined action of these two parameters leads to pronounced tunability in the spatial directivity, temporal structure, and spectral broadening of the radiation. These results help clarify the parameter-dependent mechanism of RNTS radiation under strong-field conditions and provide useful guidance for the optimization of high-brightness, highly collimated, broadband ultrafast radiation sources.