Efficient forward second-harmonic generation from planar archimedean nanospirals

Abstract

Abstract:The enhanced electric field at plasmonic resonances in nanoscale antennas can lead to efficient harmonic generation, especially when the plasmonic geometry is asymmetric on either inter-particle or intra-particle levels. The planar Archimedean nanospiral offers a unique geometrical asymmetry for second-harmonic generation (SHG) because the SHG results neither from arranging centrosymmetric nanoparticles in asymmetric groupings, nor from non-centrosymmetric nanoparticles that retain a local axis of symmetry. Here, we report forward SHG from planar arrays of Archimedean nanospirals using 15 fs pulses from a Ti:sapphire oscillator tuned to 800 nm wavelength. The measured harmonic-generation efficiencies are 2.6·10 −9 , 8·10 −9 and 1.3·10 −8 for left-handed circular, linear, and right-handed circular polarizations, respectively. The uncoated nanospirals are stable under average power loading of as much as 300 µW per nanoparticle. The nanospirals also exhibit selective conversion between polarization states. These experiments show that the intrinsic asymmetry of the nanospirals results in a highly efficient, two-dimensional harmonic generator that can be incorporated into metasurface optics.Keywords: nonlinear plasmonics, asymmetric nanoparticles, polarization conversion, metasurfaces, near-field enhancement, Archimedean nanospirals The second-order susceptibility governs a host of important nonlinear optical phenomena, including frequency mixing, sum-frequency and harmonic generation, and optical rectification. In crystalline and molecular materials, second-order nonlinearities are nonvanishing only at surfaces or in materials with a noncentrosymmetric crystal structure; moreover, the efficient generation of a second-order nonlinear effect requires that the fundamental incident and the nonlinear outgoing waves be phase matched through a macroscopic volume of material, typically on the order of cubic millimeters [1].Plasmonic nanostructures and nanostructure arrays also exhibit second-order nonlinearities, and can generate forward second harmonics if their geometries are not centrosymmetric. Such structures are inherently planar, and therefore compatible with thin-film optical and optoelectronic technologies and with metasurface optics. With advances in nanofabrication, the symmetry of the structures can be exquisitely controlled at the level of a few nanometers [2]. Combining these effects with ultrafast, high-intensity laser pulses yields massive electricfield enhancements and correspondingly greater secondharmonic yield. The localized surface plasmon resonance enhances efficiency and can be designed by selecting the nanoparticle shape for a given wavelength; selective polarization response can also be designed into the nanoparticle. A number of asymmetric plasmonic geometries have been used for harmonic generation, including L-and V-shaped nanoparticles, nanocups, and asymmetric trimers [3][4][5][6][7]. Larger plasmonic structures-such as the ratchet wheel-have also been shown to affect the polarization o...

Free‐electron Optical Nonlinearities in Plasmonic Nanostructures: A Review of the Hydrodynamic Description

“…This effective susceptibility is 20 times higher than that of lithium niobate, a commonly‐used nonlinear material. This value for the simulated nanostructures in the absence of nonlocal effects is consistent with the experimentally observed values of the effective second‐order susceptibility of metallic nanostructures of and , taking into account the differences in the local field enhancements and the surface areas. The SHG enhancement is robust with respect to geometrical scaling under the resonant excitation of the fundamental nanospiral mode which size‐dependent spectral position can be matched to the fundamental wavelength by varying α.…”

“…The effect of the quantum pressure can be seen from comparison of nonlinear response of plasmonic nanorods of different diameters or Archimedean spiral shaped nanostructures (Figures and a). Spirals have no symmetry of any kind and, hence, are good candidates for nonlinear optical interactions as they do not obey any geometrical selection rule . Initially, we consider a nonresonant excitation when the excitation frequency is lower than the lowest plasmonic resonances of both nanorods and nanospirals, in order to avoid the influence of the resonant effects.…”

Chirality and Chiroptical Effects in Metal Nanostructures: Fundamentals and Current Trends

“…The spatial distributions of local field enhancements can also play a key role in the SHG response of a material, as demonstrated in studies on Archimedean nanospirals . It was found that the intensity of SHG emission from the Archimedean nanospirals was dependent on the incident polarization and the resulting excited plasmon mode.…”

Multipolar nonlinear nanophotonics

“…where p, m and Q are the electric dipole (ED), magnetic dipole (MD) and electric quadrupole (EQ) leading moments, respectively, and ε 0 is the vacuum permittivity. Tuning the contributions of different-order multipole moments is used to engineer the scattering and tailor the emission directionality of optical nanoantennas [18,[31][32][33][34][35][36][37][38][39]. In particular, the so-called first Kerker condition for overlapped and balanced orthogonal electric and magnetic dipoles represents an example of unidirectional scattering [40] from a single-element antennas.…”