Study and control of the effects of numerical dispersion on plasma simulations of relativistic high harmonic generation

The development of laser technologies to produce extreme intensities has allowed the generation of high-order harmonics from relativistic laser-plasma mirror interactions to become attainable to observe experimentally. Numerical plasma simulations are invaluable for understanding the dynamic processes underpinning this mechanism. However, accuracy in describing high-frequency electromagnetic waves is challenging. Finite Difference Time Domain methods give rise to numerical dispersion when used to solve Maxwell’s equations, inducing a dispersive change in vacuum refractive index, which causes significant errors in physical properties of the reflected field, such as an angular deviation in the harmonic spatial profiles from the predicted specular reflection. EPOCH Particle-In-Cell (PIC) code is used to perform two-dimensional (2D) simulations to extensively study and control the effects of numerical dispersion on the generated harmonics for several Maxwell solvers. Effects on angular deviation across a range of angles of incidence and strategies to mitigate dispersive effects via controlling interaction geometry are discussed.