Optical Activation of Germanium Plasmonic Antennas in the Mid Infrared
  Impulsive interband excitation with femtosecond near-infrared pulses establishes a plasma response in intrinsic germanium structures fabricated on a silicon substrate. This direct approach activates the plasmonic resonance of the Ge structures and enables their use as optical antennas up to the mid-infrared spectral range. The optical switching lasts for hundreds of picoseconds until charge recombination red-shifts the plasma frequency. The full behavior of the structures is modeled by the electrodynamic response established by an electron-hole plasma in a regular array of antennas. 
Marco P. Fischer, Christian Schmidt, Emilie Sakat, Johannes Stock,   Antonio Samarelli, Jacopo Frigerio, Michele Ortolani, D...
cond-mat.mes-hall physics.optics