PIC simulations characterizing the Radiation Response of a Copper Target Excited by an Ultra-Short Laser Pulse.

The interaction of an intense, ultrashort-pulse laser with a solid conducting, dielectric, or semi-conducting target leads to dramatic modification of its surface and subsequent emission of electromagnetic (EM) radiation. This radiation may be an interesting probe of the laser-target interaction or useful in its own right. We have used LSP [1] particle-in-cell (PIC) simulations to characterize the low frequency (THz and below) radiation response of copper targets illuminated by single high intensity ultra-short laser pulses with intensities up to 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$. Our simulations treat the material permittivity and reflectivity using a realistic collision model [2] based on the binary collision algorithm. This permits a realistic treatment of the target's dynamically changing electromagnetic response and thermal evolution beginning from a room temperature state, which then establishes the initial conditions for the subsequent current evolution and EM emission. This work was supported in part by AFRL under award FA9451-19-C-0011. [1] Welch, D. {\&} Rose, D., Comp. Phys. Comm. \textbf{164}, 183-188 (2004) [2] A.M. Russell and D.W. Schumacher, Physics of Plasmas \textbf{24}, 080702 (2017).