Extreme terahertz electric-field enhancement in high-Q photonic crystal slab cavity with nanoholes.

A one-dimensional photonic-crystal (PC) cavity with nanoholes is proposed for extreme enhancement of terahertz (THz) electric fields using the electromagnetic (EM) boundary conditions. Both slot (for the perpendicular component of the electric displacement field) and anti-slot (for the parallel component of the electric field) effects contribute to the considerable field enhancement. The EM energy density can be enhanced by a factor of (εh/εl) in the high-refractive-index material, where εh and εl are the permittivities of the high- and low-refractive-index materials, respectively. Correspondingly, the mode volume can be reduced by a factor of 288, compared with a conventional THz PC cavity, and is three orders of magnitude smaller than the diffraction limitation. Further, the proposed THz cavity design also supports modes with high quality factors (Q) > 10, which induces strong Purcell enhancement by a factor exceeding 10. Our THz cavity design is feasible and attractive for experimental demonstrations, because the semiconductor layer in which the EM is maximized can naturally be filled with quantum-engineered active materials. Thus, the proposed design can possibly be used to develop room-temperature coherent THz radiation sources.