Abstract
Metasurfaces of gold (Au) nanoparticles on a SiO-Si substrate were fabricated for the enhancement of second harmonic generation (SHG) using electron beam lithography and lift-off. Triangular Au nanoprisms which are non-centro-symmetric and support second-order nonlinearity were examined for SHG. The thickness of the SiO spacer is shown to be an effective parameter to tune for maximising SHG. Electrical field enhancement at the fundamental wavelength was shown to define the SHG intensity. Numerical modeling of light enhancement was verified by experimental measurements of SHG and reflectivity spectra at the normal incidence. At the plasmonic resonance, SHG is enhanced up to ∼3.5 × 10 times for the optimised conditions.
Highlights
Energy up-conversion is important for a diverse range of fields, including—non-linear optics (NLO) and generation of higher laser harmonics, harvesting of long-wavelength, sub-bandgap energy light in solar cells, and photo-thermal excitation of neurons at the near-IR transparency window in tissue [1,2,3]
The phase matching conditions that are required for efficient energy transfer from the fundamental wavelength λ into higher harmonic λ/2 along the co-propagation direction are relaxed at the near-field, the efficiency of the second harmonic generation (SHG) is low
By using an array of nano-antennas on the surface of lithium niobate, it was demonstrated that the phase matching for SHG can be overcome in waveguides [10], high precision nanoscale fabrication is required
Summary
Energy up-conversion is important for a diverse range of fields, including—non-linear optics (NLO) and generation of higher laser harmonics, harvesting of long-wavelength, sub-bandgap energy light in solar cells, and photo-thermal excitation of neurons at the near-IR transparency window in tissue [1,2,3]. The phase matching conditions that are required for efficient energy transfer from the fundamental wavelength λ into higher harmonic λ/2 along the co-propagation direction are relaxed at the near-field, the efficiency of the second harmonic generation (SHG) is low. We showed that the phase control of light reflected and incident on a nanoparticle can enhance surface enhanced Raman scattering (SERS) [18,19]. This mechanism can provide an additional control for the phase sensitive SHG based on the π phase change upon reflection when light travels through the low-to-high refractive index boundary and the 0 phase change for traversing the high-to-low interface. Numerical modeling by finite difference time domain (FDTD) was carried out to reveal characteristics of light field enhancement
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