Relativistic treatment of harmonics from impurity systems in quantum   wires
  Within a one particle approximation of the Dirac equation we investigate a defect system in a quantum wire. We demonstrate that by minimally coupling a laser field of frequency omega to such an impurity system, one may generate harmonics of multiples of the driving frequency. In a multiple defect system one may employ the distance between the defects in order to tune the cut-off frequency. 
O.A. Castro-Alvaredo, A. Fring and C. Figueira de Morisson Faria