Enhanced THz field detection using a bull’s-eye plasmonic antenna.

We present a bull’s-eye plasmonic antenna for enhanced terahertz (THz) field detection in an electro-optic sampling (EOS) scheme. We use numerical simulation to optimize the antenna’s geometrical parameters to achieve a long nonlinear interaction length between a near-infrared gating pulse and locally enhanced THz field at the center of the plasmonic structure. The direct laser writing method is then employed to fabricate the gold eye-antenna on a 110-oriented gallium phosphide (GaP) substrate. The performance of the proposed nonlinear plasmonic detector is characterized with a time-resolved THz setup. Preliminary results show an improvement of the EOS detection sensitivity by 2.5 times at the plasmonic resonance frequency of around 2.5 THz.