Structural control of metamaterial oscillator strength and electric field enhancement at terahertz frequencies

Abstract

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.Over the past decade, metamaterials (MM) research has produced innumerable examples and applications of artificially engineered index of refraction and impedance across the electromagnetic spectrum. Indeed, the onset of experimental MM research gave new life to long neglected theoretical speculation into optical behavior not observed in natural materials 1 . This renewed interest quickly bore experimental fruit, of which negative index materials 2, 3 , electromagnetic cloaking 4 , perfect lensing 5, 6 , sub-diffraction imaging 7 , and perfect absorption 8, 9 are only a few paramount examples.Though quite astounding in their own right, these examples form only the tip of the MM iceberg. MMs are useful not only for engineering far-field optical behavior like that discussed above but also allow for the design and control over microscopic charge and current distributions. These near-field properties form the cornerstone for a second category of MM research, specifically based around engineering local fields inside a MM unit cell. For instance, the on-resonance charge distributions in the capacitive gaps of a split ring resonator (SRR) MM 10, 11 create localized regions inside the MM where the electric field of incident resonant radiation is greatly enhanced. These regions of electric field enhancement (EFE), when combined with

Nonlocal collective ultrastrong interaction of plasmonic metamaterials and photons in a terahertz photonic crystal cavity

“…With the damping rates for the MM (γ = 244 GHz) and cavity (κ = 10 GHz) derived from the data of Fig. 2(b) (fitted blue dashed curve) and 1b, respectively [38,39], one calculates a cooperativity factor 37. C = These values demonstrate that our experiment indeed reaches the ultrastrong coupling regime.…”

Voltage-tunable dual-layer terahertz metamaterials

“…Because the tunable response of the BC-SRRs is based on inductive and capacitive coupling, we can modulate the response with the lateral shift, even though there is a large resonant frequency mismatch between the resonators. In an extreme case, a tunable amplitude response can be achieved with an SRR and a non-resonance closed ring 39 . However, if we require both large frequency tuning and amplitude tuning, then resonant frequency matching should be achieved.…”

“…One can mount different resonator structures, rather than SSRs, on the two layers to realize diverse functions. For instance, one layer of the metamaterials could be a closed ring array 39 to allow for dynamic manipulation of the metamaterial oscillator strength and electric field enhancement factor, with the lateral shift controlled by the comb-drive actuator. Moreover, the dimension of the resonators can be scaled to construct devices working at other frequency regimes.…”

Terahertz quantum plasmonics at nanoscales and angstrom scales

“…On the other hand, recent development of nanofabrication technology brings a large impact on various photonic researches including terahertz plasmonics [24][25][26][27][28][29][30][31][32][33]. Artificially designed metal structures in subwavelength scale are used to manipulate the response of the terahertz field, realizing a wide range of applications in sensors [30,31,[34][35][36][37], switches [38][39][40][41], and filters [42][43][44][45].…”