Generation of widely tunable continuous-wave terahertz radiation using a two-dimensional lattice of nonlinear metallic nanodimers

We propose an alternative technique of continuous-wave terahertz radiadion generation based on light scattering by a two-dimensional flat lattice of nonlinear metallic nanodimers. We show that it may be accompanied by plasmon-driven modulation instability of the lattice polarization resulting in periodic oscillations of both transmitted and reflected light envelopes. We find that the modulation frequency lies in the terahertz band and can be tuned within a wide range, from units up to several tens of terahertz, by varying of the incident light intensity and frequency. We also compare the suggested method with traditional one based on optical heterodyne downconversion.

Figure 1

(Color online) Schematic sketch demonstrating light scattering by a two-dimensional lattice of nonlinear metallic nanodimers in a self-modulation regime. Inset shows electrical dipole moment ${\mathbf{p}}_{\perp }$ of the dimer transverse dipole eigenmode excited by the incident wave and magnetic dipole moment ${\mathbf{m}}_{\perp }$ of the dimer transverse quadrupole eigenmode excited due to plasmon-driven instability of the dimer transverse dipole eigenmode. Indexes “i,” “r,” and “t” correspond to incident, reflected, and transmitted waves, respectively.

Figure 2

(Color online) (a) Reflection and (b) transmission spectra for the considered nanostructure at different intensities of the incident wave. Dashed and dotted curves depict the branches which are unstable with respect to small perturbations of $P_{\perp }$ and $M_{\perp }$, respectively. (c) The regions of electric (I) and magnetic $\left(\text{II}+\text{III}\right)$ instabilities in the plane of incident wave parameters “intensity-frequency.” Areas (II) and (III) indicate zones of magnetic instability growth leading to stationary and self-modulation regimes, respectively. For the considered case (silver nanodimers in the ${\text{SiO}}_2$ host) $\hslash {\omega }_0=3.14\text{eV}$. We assumed $l=73\text{nm}$ and $b=\pi /k_s$.

Figure 3

(Color online) (a) The time dependences of reflectance (1) and transmittance (2) of the 2D lattice of nonlinear silver nanodimers embedded in ${\text{SiO}}_2$ host during the instability growth at $\hslash \omega =3.091\text{eV}$. Curve (3) shows the temporal dependence of $I_i$, slowly growing with the saturation value $I_i^{sat}=14.44\text{MW}/{\text{cm}}^2$. (b) Dependences of the fundamental harmonic of the self-oscillations $f_{sm}$ on $I_i$ at the different incident light frequencies: (1) $\hslash {\omega }_1=3.091\text{eV}$; (2) $\hslash {\omega }_2=3.081\text{eV}$; (3) $\hslash {\omega }_3=3.066\text{eV}$. Lattice parameters are the same as in Fig. 2.