The interactions of ultra-intense lasers with solid targets with nanowires received a lot of attention because they appear to show potentials to increase the laser light absorption rate. Laser-nanowire interactions open up various applications such as attosecond bunch generation, enhanced x-ray generation, brilliance gamma-ray yield, as well as efficient micro fusion. Despite many studies on this topic, either numerically or experimentally, the electron dynamics under the action of a strong laser field across the nanowire remain unclear.
We report our observation of the electron transport inside the nanowire when irradiated by the intense laser pulse. We found that a plasma wakefield is excited by the double frequency electron bunches. These fast electron bunches are generated by the J X B heating of the linearly polarized laser pulse at the tip of the nanowire. This wakefield has an amplitude of the order of TV/m, oscillating at the plasma frequency, and propagates into the nanowire. Electrons injected at the later stage are accelerated by the wakefield when the right initial conditions are satisfied. In addition, we observed the quiver of the electrons across the nanowire under the action of the electric field normal to the nanowire surface. This electron crossing served as the secondary drive bunch and facilitates deeper wakefield propagation in the nanowire. We show the detail of electron transport by using 2D and 3D Particle-In-Cell (PIC) code EPOCH and PICONGPU. The acceleration of these bunches has generally increased the electron energy absorption by more than 2 times as compared to a flat target.