Particle-in-cell simulations of laser-plasma interactions at solid densities and relativistic intensities: the role of atomic processes

摘要

Direct studies of intense laser-solid interactions is still of greatchallenges, because of the many coupled physical mechanisms, such as directlaser heating, ionization dynamics, collision among charged particles, andelectrostatic or electromagnetic instabilities, to name just a few. Here, wepresent a full particle-in-cell simulation (PIC) framework, which enables us tocalculate laser-solid interactions in a "first principle" way, covering almost"all" the coupled physical mechanisms. Apart from the mechanisms above, thenumerical self-heating of PIC simulations, which usually appears insolid-density plasmas, is also well controlled by the proposed"layered-density" method. This method can be easily implemented into thestate-of-the-art PIC codes. Especially, the electron heating/acceleration atrelativistically intense laser-solid interactions in the presence of largescale pre-formed plasmas is re-investigated by this PIC code. Results indicatethat collisional damping (even though it is very week) can significantlyinfluence the electron heating/acceleration in front of the target. Furthermorethe Bremsstrahlung radiation will be enhanced by $2\sim3$ times when the solidis dramatically heated and ionized. For the considered case, where laser is ofintensity $10^{20}\ \text{W}/\text{cm}^2$ and pre-plasma in front of the solidtarget is of scale-length $10\ \mu\text{m}$, collision damping coupled withionization dynamics and Bremsstrahlung radiations is shown to lower the"cut-off" electron energy by $25\%$. In addition, the resistive electromagneticfields due to Ohmic-heating also play a non-ignorable role and must be includedin real laser-solid interactions.