Strongly enhanced and directionally tunable second-harmonic radiation from a plasmonic particle-in-cavity nanoantenna

Abstract

Second-harmonic (SH) generation is tremendously important for nonlinear sensing, microscopy and communication system. One of the great challenges of current designs is to enhance the SH signal and simultaneously tune its radiation direction with a high directivity. In contrast to the linear plasmonic scattering dominated by a bulk dipolar mode, a complex surface-induced multipolar source at the doubled frequency sets a fundamental limit to control the SH radiation from metallic nanostructures. In this work, we harness plasmonic hybridization mechanism together with a special selection rule governing the SH radiation to achieve the high-intensity and tunable-direction emission by a metallic particle-in-cavity nanoantenna (PIC-NA). The nanoantenna is modelled with a first-principle, self-consistent boundary element method, which considers the depletion of pump waves. The giant SH enhancement arises from a hybridized gap plasmon resonance between the small particle and the large cavity that functions as a concentrator and reflector. Centrosymmetry breaking of the PIC-NA not only modifies the gap plasmon mode boosting the SH signal, but also redirects the SH wave with a unidirectional emission. The PIC-NA has a significantly larger SH conversion efficiency compared to existing literature. The main beam of the radiation pattern can be steered over a wide angle by tuning the particle's position. * ljiang@eee.hku.hk † wsha@eee.hku.hk

Maxwell–Hydrodynamic Model for Simulating Nonlinear Terahertz Generation From Plasmonic Metasurfaces

“…The glass substrate and ITO layer are chosen as nondispersive dielectric materials and the relative permittivity are 2.25 and 3.8, respectively. The parameters for gold are taken to be n0 = 5.92×10 28 m -3 and γ = 10.68×10 13 rad/s. The dimensions of the SRRs are chosen as shown in Fig.…”

“…The nonlinear response can be described with material nonlinear polarization, i.e. P=ε 0 χ (n) E n , where χ (n) is the nonlinear susceptibility [12,13]. Alternatively, a hydrodynamic model in time-domain can be used to model nonlinear effects resulting from motion of conduction electrons in metals.…”

“…In this paper, a self-consistent parallel ADE-FDTD method is employed in conjugation with the hydrodynamic model to simulate the nonlinear THz emission from plasmonic metasurfaces. Compared to the Maxwell-hydrodynamic model in literature [14,23] and our previous work [12,13,24], a new two-step splitting scheme is proposed to solve the multiphysics model. In Ref.…”

Mixing of spin and orbital angular momenta via second-harmonic generation in plasmonic and dielectric chiral nanostructures

“…We consider a chiral cluster of nanospheres with N -fold rotation symmetry, which is surrounded by air and irradiated by a circularly polarized LG beam carrying spin and orbital angular momentum, as shown in Fig 1 . We calculate numerically the light scattering at the fundamental frequency (FF) and SH from plasmonic and dielectric nanostructures using the boundary element method [32]. Only the surface contribution to the SHG is considered for centrosymmetric materials [33][34][35].…”

Sum-frequency and second-harmonic generation from plasmonic nonlinear nanoantennas

“…However, tailoring the radiation pattern of nonlinear nanoantennas has great challenges. First, nonlinear radiation exhibits complex multi-polar interactions [15,16]. Second, currently, few tools are available for effi cient and rigorous analyses of surface nonlinear scattering processes in complex structures.…”