Time-derivative Lorentz materials and their utilization as electromagnetic absorbers

A time-derivative Lorentz material model is introduced for the polarization and magnetization fields in a complex medium illuminated by an ultrafast pulsed beam. This model represents a straightforward generalization of the standard Lorentz material model to include the time derivatives of the fields as driving mechanisms. The Green function for this material is derived and used to demonstrate that it is causal and passive. An electromagnetic absorber is constructed with this time-derivative Lorentz material, and simulations are given which illustrate its effectiveness under illumination by obliquely incident, ultrafast, pulsed Gaussian beams having narrow and broad waists.