3D FDTD simulation of photoconducting switches

Summary form only given. Extending the FDTD (finite-difference time-domain) method of Taflove (1990), the authors have constructed a 3D electromagnetic model for the simulation of fast photoconductive switches excited by ultrashort optical pulses. These are coupled to pulse forming networks for the optimized control of the pulse width. The switches consist of microstrip metal transmission lines laid down on a GaAs substrate. A 5 to 50 /spl mu/m wide gap divides a piece of the line that is charged to a few volts from a continuation of the line that is grounded. A 0.1 to 0.3 ps, 1 pJ, 0.6 /spl mu/m laser pulse generates the order of 10/sup 17/ cm/sup -3/ electron/hole densities in the substrate material to close gap, thereby launching a 1 to 3 ps pulse. Electromagnetic coupling to the networks truncates the pulse on comparable time scales. Maxwell´s equations with drift diffusion have been solved, and the effects of alternative numerical treatments of the boundary conditions, electromagnetics, and transport have been explored.