Spatial characteristics of nonlinear Thomson scattering from tightly focused single-cycle laser pulse with varied initial phases

Nonlinear Thomson scattering in intense (𝑎0 = 6) single-cycle (𝐿0 = 1𝜇𝑚) Gaussian laser pulse is investigated theoretically and numerically that demonstrates varied spatial characteristics in the tightly focused (𝑏0 = 3𝜇𝑚) regime. In the above ultrashort laser pulse, the electron has the potential to radiate single attosecond pulse with almost infinite SNR which is highly robust to varied initial phases. Furthermore, a novel symmetry degradation phenomenon in the tightly focused domain is firstly discovered, where the fourfold symmetric spatial radiation pattern in non-tightly focused pulses respectively degrades to plane/linear symmetry radiation pattern in the spherical projected/polarized plane. While spatial radiation is highly sensitive to initial phases, we remarkably find that the difference of peak radiation’s polar angles 𝜙m exactly equals to that of incident laser’s initial phases 𝜙0, indicating the initial phase has phase/angle shift effect on the electron’s spatial motion and radiation. With numerical analysis, the sampling results demonstrate that peak radiation’s polar angle 𝜃m and the difference 𝜙m = 𝜙0 are constant regardless of initial phases.