  We demonstrate a full-wave numerical Maxwell-Bloch simulation tool including
perfectly matched layer (PML) absorbing boundary conditions. To avoid
detrimental reflection errors at the boundary of the simulation domain, an
adapted PML model is introduced, which takes into account impedance mismatch
effects arising from the internal quantum system. For the numerical validation
of the modified PML model the simulation tool is applied to the active gain
medium of a terahertz quantum cascade laser (QCL) structure. Improved absorbing
characteristics for the truncation of active gain media in our Maxwell-Bloch
simulation approach are obtained.
