Harnessing complexity: Nonlinear optical phenomena in L-shapes, nanocrescents, and split-ring resonators

Area of Science:

• Plasmonics and Nanophotonics
• Nonlinear Optics
• Computational Physics

Background:

• Plasmonic nanoparticles exhibit unique optical properties influenced by their shape and symmetry.
• Understanding nonlinear optical responses is key for advanced photonic devices.
• C2v symmetry in nanoparticles offers specific selection rules for optical phenomena.

Purpose of the Study:

• To systematically investigate the linear and nonlinear optical characteristics of C2v-symmetric plasmonic nanoparticles.
• To analyze the second harmonic generation (SHG) and terahertz (THz) generation.
• To develop an analytical theory for predicting nonlinear optical responses.

Main Methods:

• Finite-difference time-domain (FDTD) method for optical property simulation.
• Semiclassical hydrodynamic model accounting for nonlocal and nonlinear effects.
• Analytical theory development and comparison with numerical results.

Main Results:

• Three distinct C2v-symmetric shapes (L-type, crescent, π-shaped) show prominent plasmon modes.
• Strong polarization-dependent SHG was observed, governed by nanoparticle geometry and C2v symmetry.
• Efficient broadband THz generation was achieved through difference-frequency generation, linked to plasmonic resonances.

Conclusions:

• C2v symmetry dictates SHG polarization states and selection rules.
• The proposed analytical theory accurately predicts THz generation, offering insights into nonlinear optical phenomena.
• These plasmonic nanostructures show potential for applications in nonlinear spectroscopy, nanophotonics, and optoelectronics.