Emission spectrum of a mesoscopic ring driven by fast unipolar pulses

We perform a theoretical study of the emission properties of a thin ballistic, mesoscopic ring driven by a quasi-periodic train of electromagnetic half-cycle pulses (HCPs). It is shown that an applied sequence of pulses induces a non-equilibrium, time-dependent charge polarization in the ring. The resulting charge oscillations generate an emission spectrum that can be modified by designing appropriately the strength and the shape of the HCP sequence. The HCP is fast in that, the relaxation of the excited ring to its equilibrium state occurs after the pulses have passed by. Hence the study of the emission spectrum offers a novel possibility to investigate relaxation processes in mesoscopic systems in absence of external perturbations