The response of ion plasmas to external radiation fields is investigated in a quantum mechanical formalism. We focus on the total electric field within the plasma. For general bandpass signals three frequency regions can be distinguished in terms of the plasma frequency. For low frequencies, the external field is shielded. For high frequencies, the field is not modified. Resonant behavior of the plasma appears for frequencies near the plasma frequency: large internal electric fields and induced currents are present. These effects may be relevant for biological systems. The model is therefore extended to a two-species plasma and additional interactions are studied. The response is not essentially altered. To make the models more realistic, a so-called bath is included. In the weak coupling approximation the resonance frequency is shifted and some damping occurs. Finite temperature effects on the electric field are absent. The energy of the system, however, depends on temperature.