  We present a density-based topology optimization scheme for locally
optimizing the electric power dissipation in nanostructures made of lossy
dispersive materials. By using the complex-conjugate pole-residue (CCPR) model,
we can accurately model any linear materials' dispersion without limiting to
specific material classes. We incorporate the CCPR model via auxiliary
differential equations (ADE) into Maxwell's equations in the time domain, and
formulate a gradient-based topology optimization problem to optimize the
dissipation over a broad spectrum of frequencies. To estimate the objective
function gradient, we use the adjoint field method, and explain the
discretization and integration of the adjoint system into the finite-difference
time-domain (FDTD) framework. Our method is demonstrated using the example of
topology optimized spherical nanoparticles made of Gold and Silicon with an
enhanced absorption efficiency in the visible-ultraviolet spectral range. In
this context, a detailed analysis of the challenges of topology optimization of
plasmonic materials associated with a density-based approach is given.
