Nonlinear Thomson scattering from a tightly focused circularly polarized laser with varied incident-pulse durations

In this paper, nonlinear Thomson scattering in an intense () tightly focused () Gaussian laser pulse is theoretically and numerically investigated to demonstrate varying spatial characteristics in the few-cycle and multi-cycle domains. We find that within ultrashort incident laser pulses, electrons have the potential to radiate a single attosecond pulse with a large signal-to-noise ratio, which turns into a train of attosecond pulses with a multi-cycle laser. Furthermore, a novel asymmetry phenomenon is discovered for the first time in the few-cycle domain whereby spatial radiation lasts for only one circle with apparent peaks and valleys, in contrast to the helical radiation pattern apparent in the multi-cycle domain, which gradually turns into a common fourfold-symmetry pattern. This means that the difference between tightly and non-tightly focused laser pulses can be bridged utilizing an appropriate incident pulse duration under specific conditions. The above difference is demonstrated again in the polar plane, where electrons change from a light-spot to a light-band radiation feature when the incident pulse duration increases.