The simulations used in this work were all done using the finite-difference timedomain (FDTD) method. One of a fairly large number of methods and variations on methods applicable to the simulation of electromagnetic fields, the FDTD is particularly simple and intuitive, and its application is well adapted to computation of high-frequency electromagnetic fields. The FDTD method approximates the electromagnetic-field equations directly without the need for intermediate steps such as the approximation and minimization processes that are so important in many numerical computation methods such as the finite-element methods.