Nonlinear Light Amplification Governed by Structural Asymmetry

Abstract

Among these studies, maneuvering the structural asymmetry offers a complementary solution of manipulating optical excitation, subsequent energy coupling, and reemission of resonant modes. [8][9][10][11][12][13][14][15] For instance, this treatment in plasmonic and dielectric nanostructures frequently triggers new optical resonant modes, such as magnetic dipole resonances, [8,9] high-Q Fano resonances, [16,17] and bound states in the continuum, [18,19] resulting in huge nearfield enhancements over a wider operating bandwidth with respect to symmetrical counterparts. As an essential part of nonlinear frequency conversions, second-harmonic generation (SHG) generally calls for media featuring the reduced symmetry under the dipole approximation, [1,6,8,20,21] and has thus been vigorously investigated in these asymmetrical nanodevices. [8,9,[16][17][18][19] However, when the energy coupling is extended to nonlinear polarizations, structural asymmetries may also complicate the efficient nonlinear light amplification. The primary reason lies in the structural asymmetry-induced distortion of energy-coupling (cross-coupling) channels in SHG processes. [11,22] This distortion may result in the reduced spatial overlapping or spectral mismatch of optical resonant modes as well as the alteration of nonvanishing susceptibility elements, which prompt macroscopic nonlinear signals in the far field to diminish. Therefore, finding an efficient and tunable platform, which permits the enlargement of intrinsically weak nonlinear optical responses in structural asymmetry-mediated manners, still remains a great challenge in nanophotonics. Furthermore, less studied nanosystems, partly due to their limited conversion efficiencies and critical fabrication challenges, are sufficient to establish a theoretical model able to quantify the contribution of structural asymmetries to plasmon-driven nonlinear light amplifications.To tackle these challenges, here we demonstrate a 3D capshaped nanoparticles, namely, AlNanocaps, by integrating aluminum materials with large-area periodic geometries, as reproducible generators of second-harmonic lights. We experimentally show that, by properly breaking the centrosymmetry of AlNanocaps, the SHG emission of proposed configurations greatly outperforms that of symmetrically oriented counterparts. Through regulating several structural parameters (e.g., asymmetry orientations, component materials, etc.) and resolving relative polarization dependences, we demonstrate that structural asymmetries can simultaneously alter the Maneuvering the structural asymmetry in metasurfaces plays an essential role in nonlinear nanophotonics, particularly in sub-wavelength-scale harmonic generation. Here, a highly efficient and reproducible plasmonenhanced second-harmonic generation platform for exploring these quantitative contributions of structural asymmetries to the amplification of inherently weak nonlinear responses is experimentally designed. It is discovered that such structural asymmetries can not only quantitatively ...

Supplementary document for Substrate-mediated plasmon hybridization toward high-performance light trapping - 6328622.pdf

“…4(c), these indeed exist a rotation of emission coils in ASD(N)Gs, in which the orientation of polar plots is slightly tilted from 90° (270°), e.g., by ∼ 15° for ASD(10)G. As depicted in the inset of Fig. 4(a), while referring to previous works [4,5], we assume two SHG contributions that are projected onto the analyzing polarizer, i.e., one polarized along the x-[α = 90° (270°)] and the other one along the y-axis direction [α = 0° (180°)]. Then, recorded SHG signals in the dependence of azimuthal angles (α) can be described by…”