Control of terahertz nonlinear transmission with electrically gated graphene metadevices

Abstract

Graphene, which is a two-dimensional crystal of carbon atoms arranged in a hexagonal lattice, has attracted a great amount of attention due to its outstanding mechanical, thermal and electronic properties. Moreover, graphene shows an exceptionally strong tunable light-matter interaction that depends on the Fermi level - a function of chemical doping and external gate voltage - and the electromagnetic resonance provided by intentionally engineered structures. In the optical regime, the nonlinearities of graphene originated from the Pauli blocking have already been exploited for mode-locking device applications in ultrafast laser technology, whereas nonlinearities in the terahertz regime, which arise from a reduction in conductivity due to carrier heating, have only recently been confirmed experimentally. Here, we investigated two key factors for controlling nonlinear interactions of graphene with an intense terahertz field. The induced transparencies of graphene can be controlled effectively by engineering meta-atoms and/or changing the number of charge carriers through electrical gating. Additionally, nonlinear phase changes of the transmitted terahertz field can be observed by introducing the resonances of the meta-atoms.

Electrically Controllable Terahertz Second‐Harmonic Generation in GaAs

“…Additionally, engineering efforts aimed at achieving a longer interaction length, instead of a deep-subwavelength interaction length of the photoconductive layer, may significantly improve the efficiency. Furthermore, instead of doped GaAs, other materials with high nonlinearities, such as graphene, [18,21,22] may also be utilized for electric-field-induced nonlinear processes at THz frequencies. Through these improvements and investigations, the electric-field-induced nonlinear process will present a new route for developing nonlinear optical devices in the THz spectral range, thereby further enhancing the capabilities of THz science and technology.…”

“…sources of THz optical nonlinearities, one of the most promising is the nonlinear response of carriers in semiconductors and graphene to an intense THz field. [13][14][15][16][17][18][19][20][21][22] This nonlinear behavior is attributed to energydependent scattering during carrier drift transport. By utilizing the highly nonlinear response of carriers, various nonlinear optical phenomena have been observed at THz frequencies, such as absorption bleaching, [13][14][15][16][17][18] self-phase modulation, [19] and harmonic generation.…”

“…[13][14][15][16][17][18][19][20][21][22] This nonlinear behavior is attributed to energydependent scattering during carrier drift transport. By utilizing the highly nonlinear response of carriers, various nonlinear optical phenomena have been observed at THz frequencies, such as absorption bleaching, [13][14][15][16][17][18] self-phase modulation, [19] and harmonic generation. [20][21][22] However, the carriers in the majority of demonstrated materials and devices [13][14][15][16][17][18][19][20][21][22] are accelerated symmetrically with respect to the direction of an incident THz field, which results in a nonlinear optical response that is solely describable with odd-order or mostly thirdorder susceptibilities.…”

“…By utilizing the highly nonlinear response of carriers, various nonlinear optical phenomena have been observed at THz frequencies, such as absorption bleaching, [13][14][15][16][17][18] self-phase modulation, [19] and harmonic generation. [20][21][22] However, the carriers in the majority of demonstrated materials and devices [13][14][15][16][17][18][19][20][21][22] are accelerated symmetrically with respect to the direction of an incident THz field, which results in a nonlinear optical response that is solely describable with odd-order or mostly thirdorder susceptibilities. [23] Second-order nonlinear processes for THz waves, such as THz second-harmonic generation (SHG), have also been observed in a few early pioneering studies.…”

Nonlinear THz spectroscopy and simulation of gated graphene

“…Recent progress in THz graphene research has shown that even at modest fields on the order of tens of kV/cm a field dependent increase in transmission can be observed due to a nonlinear response of the excited carriers [8,[9][10][11][12][13][14]. With high field THz setups and high mobility large-area graphene samples more commonly available, the study of nonlinear THz properties has intensified significantly.…”