FDTD simulation of a partially-coherent Gaussian Schell-model beam

We describe the FDTD implementation of quasi-monochromatic Gaussian Schell model (GSM) beam incidence, which is frequently used to model partial coherence effects in lasers. The cross-spectral density of the GSM beam is subjected to coherent mode decomposition, and each coherent mode is simulated in a separate FDTD run using the plane-wave decomposition (or angular-spectrum) method. The output intensity associated with every coherent-mode excitation is then added to yield the final intensity, because of the statistical independence of the modes. A simple example is presented to show the potential functionality of the technique.