On the basis of the finite-difference time domain method, we have calculated the temporal evolution of the electromagnetic field inside a waveguide system that is bounded by perfectly conducting walls. Part of the waveguide is filled with an active medium whose amplifying properties resulting from stimulated emission processes are modeled by introducing a frequency-dependent conductivity to Maxwell’s equations. An electric noise current that is randomly distributed throughout the gain region is used to model spontaneous emission processes. The feedback provided by the reflections from the walls of the waveguide and the interfaces between the active part and the adjacent vacuum leads to lasing for a sufficiently strong gain medium. Besides this conventional feedback, we also use rough walls for the part of the waveguide that is filled with the gain medium and investigate the influence of this roughness on the output intensity, the frequency spectrum of the emitted light, and the lasing threshold.
© 2004 Optical Society of America
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