Modulating Polarization in Second Harmonic Generation through Symmetry Evolution in Plasmonic Lattices.

Area of Science:

• Plasmonics
• Nonlinear Optics
• Materials Science

Background:

• Plasmonic nanostructures offer unique electromagnetic field confinement.
• Second Harmonic Generation (SHG) is a key nonlinear optical process.
• Controlling SHG efficiency in plasmonic systems is crucial for device applications.

Purpose of the Study:

• To develop a cost-effective method for fabricating centimeter-scale plasmonic square lattices with tunable unit structures.
• To investigate the influence of structural symmetry on SHG enhancement.
• To explore the potential for designing efficient nonlinear plasmonic devices.

Main Methods:

• Fabrication of plasmonic square lattices with varying unit symmetries (circles, crosses, circle-cross pairs) on a centimeter scale.
• Characterization of electromagnetic field distribution and SHG signals under oblique incidence.
• Analysis of SHG conversion efficiency and its dependence on unit structure symmetry.

Main Results:

• Achieved tunable plasmonic square lattices with circle, cross, and circle-cross pair units.
• Demonstrated progressive SHG enhancement with decreasing unit symmetry (C∞ > C4 > C2).
• Observed a peak SHG conversion efficiency of 1.0 × 10⁻², a 7.3-fold enhancement for circle-cross pairs, comparable to bulk nanostructures.

Conclusions:

• Structural symmetry plays a critical role in dictating SHG enhancement in plasmonic lattices.
• The Bloch-surface plasmon polariton (Bloch-SPP) modes contribute to the high SHG efficiency.
• This work provides a pathway for designing advanced functional nonlinear plasmonic devices.