Keiser, G. R.5; Seren, H. R.5; Strikwerda, Andrew C.1; Zhang, X.5; Averitt, R. D.4
1 Department of Photonics Engineering, Technical University of Denmark2 Teraherts Technologies and Biophotonics, Department of Photonics Engineering, Technical University of Denmark3 Boston University4 University of California, San Diego5 Boston University
The design of artificial nonlinear materials requires control over internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists of a split ring resonator (SRR) array stacked above an array of closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results in an increase of the MM oscillator strength by a factor of 4 and a 40% change in the amplitude of the resonant electric field enhancement in the SRR capacitive gap. We use terahertz time-domain spectroscopy and numerical simulations to confirm our results. We show that the observed electromagnetic response in this MM is the result of image charges and currents induced in the closed rings by the SRR. (C) 2014 AIP Publishing LLC.