Our physical motivation is to simulate an optical trap formed by multiple ultra-high-intensity laser beams, to create conditions favourable for the production of electron–positron pairs.
We simulate this process in a 3D box. One of the important tasks is to set the boundary conditions describing the multiple incident beams properly, based on the design of the optical trap inside the box. Practically, this means back-propagating a prescribed field profile to the boundaries. A general solution to this problem is given by Rayleigh–Sommerfeld diffraction, and more advanced routines based on this approach already exist. Once we have reconstructed the correct boundary conditions, we need to verify that they consistently reproduce the optical trap using the Cartesian solver of Maxwell’s field equations (part of the PIC code Smilei in our case). The goal of this work is to adapt these approaches to our case and test them.