Improvement of the laser module in the quasi-static PIC code QuickPIC

Simulations of laser-plasma interactions in plasma-based acceleration (PBA) typically require three-dimensional kinetic modeling via the particle-in-cell (PIC) method. While fully explicit 3D PIC codes provide first-principles accuracy, resolving the short laser wavelength(∼ 1µm ) over a long acceleration distance (∼ 100mm ) is computationally expensive. The quasi-static approximation (QSA) mitigates this limitation by decoupling the timescales for the laser evolution and the plasma response, permitting time step for advancing the laser larger than the Courant-Friedrichs-Lewy (CFL) limit. In this article, we implement a new laser envelope solver that uses finite-difference (FD) method in the QSA code QuickPIC. We also couple the solver to a particle-based Ammosov--Delone--Krainov (ADK) field-ionization model for laser-driven ionization. Benchmark simulations against the full-PIC code OSIRIS demonstrate that the new FD-based solver is capable of accurately simulating plasma based accelerator scenarios such as relativistic self-focusing, wakefield excitation, photon acceleration, and field ionization through the laser pulse. Compared with the old laser solver in QuickPIC, the new algorithm is more stable when simulating plasma wakes with large laser amplitude.