Plasma dynamics of nanowire array irradiated by relativistic femtosecond laser pulses

Shih Wei Wang^1*, Shih Hung Chen¹, Chih Hao Pai¹

¹Department of Physics, National Central University, Taoyuan, Taiwan

* Presenter:Shih Wei Wang, email:26steven0801@gmail.com

In recent years, interactions between intense laser pulses and nanostructured targets, such as foam, nanospheres, or nanowires, have been extensively studied. Enhancement of laser energy absorption rate due to surface nanostructures on solid targets was demonstrated by both simulations and experiments. Nanowire (NW) targets, in particular, allow deep penetration of laser pulse into the target surface and provide a larger interaction surface area for laser energy absorption due to their high aspect ratios. The efficient heating from the NW surface structure could significantly promote the feasibility of proton-boron fusion technology. However, the relation between NW target geometry, i.e., the diameter of NWs and the spacing, affects laser energy absorption efficiency has yet to be fully clarified.
In this work, we systematically investigate the interaction between NW targets and relativistic laser pulses through three-dimensional particle-in-cell simulations. The laser pulse duration and the intensity are 35 fs, and 6×10¹⁹ W/cm² respectively. NW targets are composed of cold, unionized boron atoms.
We first examine the enhancements of laser solid target heating from NW surface structure in terms of electron temperature, ionization rate, and laser energy absorption. Most notably, laser energy absorption is approximately six times higher compared to flat targets. In addition, using simplified simulation models (3×3 NW array), we then identify the different stages of laser-plasma interaction. The laser absorption can be mainly attributed to the Brunel mechanism and J×B acceleration of electrons. The simulation results also reveal the local field enhancement effect of NW arrays due to polarization charges. Based on the underlying heating mechanisms, we can determine the proper NW target geometry for optimal laser energy absorption.

Keywords: Ultraintense lasers, Ultrafast laser technology, p-B fusion, Nanowire structure