J. F. Ong, P. Ghenuche, and K. A. Tanaka [ https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.033262 ]
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. Many studies have experimentally shown enhanced laser energy absorption on a solid target covered by nanowires. The absorption mechanism at the nanoscale is not fully understood and exhibits a distinct behavior following the irradiation of an intense laser pulse.
In this study, we found clear evidence of large-amplitude particle-driven wakefield excitation inside a solid-density nanowire by using particle-in-cell simulations. The wakefield is excited by the double frequency fast electron bunches from the JxB mechanism 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 also 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.
Wakefield excitation inside 300 nm diameter nanowire upon irradiation using 22 fs and a0=68 laser pulse. Electrons are stripped off from the surface of the nanowire and moved to the right (forward current, blue). The return current (red) is created at the surface of the nanowire. A plasma wave is excited inside the nanowire as indicated by the periodic structure current.