Lasers concentrate light by trapping it within a cylinder of reactive semiconducting material and bouncing it back and forth between mirrors placed at both ends. The extraordinary intensity of lasers owes to the uniformity of this emission. While suitable for conceptual designs, theoretical modelers such as Hess argue that these methods lack the precision required for optimizing microtechnology. They must be solved almost simultaneously so that the results from each set continually feeds into the other.
Sophisticated methods exist for modeling the electronics.
What remains to be tackled are the optics. Here's where the Green's function comes in. A equals the field at point B plus the field at point C, and so on. They then solve the resulting set of equations to obtain a solution for the system at all of the points. When the engineers are refining a laser design, their code races through the calculations that generate the equations defining the mesh points.