A new method for solving the transverse part of the free-space Maxwell equations in
three dimensions is presented. By taking the Helmholtz decomposition of the electric
field and current sources and considering only the divergence-free parts, we obtain an
explicit real-space representation for the transverse propagator that explicitly
respects finite speed of propagation. Because the propagator involves convolution
against a singular distribution, we regularize via convolution with smoothing kernels
(B-splines) prior to sampling based on a method due to Beyer and LeVeque (1992).
We show that the ultimate discrete convolutional propagator can be constructed to
attain an arbitrarily high order of accuracy by using higher-order regularizing kernels
and finite difference stencils and that it satisfies von Neumann’s stability condition.
Furthermore, the propagator is compactly supported and can be applied using
Hockney’s method (1970) and parallelized using the same observation as made by
Vay, Haber, and Godfrey (2013), leading to a method that is computationally
efficient.