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Localized and propagating surface plasmon resonances in aperture-based third harmonic generation.
Optics Express
|December 25, 2015
Summary
Optimizing surface plasmons in metal films enhances third harmonic generation. Tuning localized and propagating resonances to specific wavelengths significantly boosts conversion efficiency for plasmonic metasurfaces.
Area of Science:
- Plasmonics
- Nonlinear Optics
- Metasurfaces
Background:
- Surface plasmons, collective oscillations of electrons in metals, can enhance light-matter interactions.
- Third harmonic generation (THG) is a nonlinear optical process where three photons of the fundamental frequency combine to form one photon of the third harmonic frequency.
- Plasmonic metasurfaces offer unique optical properties due to their subwavelength structures.
Purpose of the Study:
- To investigate the influence of localized and propagating surface plasmons on THG from rectangular apertures in metal films.
- To identify optimal aperture array structures for maximizing THG efficiency.
- To establish design criteria for efficient harmonic generation from plasmonic metasurfaces.
Main Methods:
- Finite-difference time-domain (FDTD) simulations were employed to design optimal aperture array structures.
- Nonlinear scattering theory guided the simulation and design process.
- Fabrication and experimental measurement of THG from designed structures were performed.
Main Results:
- The highest THG conversion efficiency was achieved when localized surface plasmon resonance (LSPR) was tuned to the fundamental wavelength and propagating (Bragg) resonance was tuned to the third harmonic wavelength.
- This optimal configuration resulted in a 2.5-fold increase in THG efficiency compared to tuning both resonances to the fundamental wavelength.
- Tuning Bragg resonance to the third harmonic improved directivity for THG emission collection, while tuning LSPR to the third harmonic was less beneficial due to gold absorption.
Conclusions:
- The study demonstrates that careful tuning of localized and propagating surface plasmon resonances is crucial for optimizing THG in plasmonic metasurfaces.
- The findings provide an optimal design criterion for enhancing harmonic generation efficiency in thin plasmonic structures.
- Quantitative agreement between experimental results and theoretical analysis validates the proposed design approach.
