  Ultracold quasineutral plasmas generated in the laboratory are generically
inhomogeneous and ex- hibit small charge imbalances. As will be demonstrated,
via a hydrodynamic theory as well as microscopic simulations, the latter lead
to efficient energy absorption at the plasma boundary. This proposed
"edge-mode" is shown to provide a unified explanation for observed absorption
spectra measured in different experiments. Understanding the response of the
electronic plasma compo- nent to weak external driving is essential since it
grants experimental access to the density and temperature of ultracold plasmas.
