Harmonic Generation up to Fifth Order from Al/Au/CuS Nanoparticle Films

Area of Science:

• Plasmonics
• Nonlinear Optics
• Materials Science

Background:

• Dual heterostructures with noble-metal and copper chalcogenide nanoparticles enhance light-matter interactions via coupled localized surface plasmon resonances (LSPRs).
• Previous work demonstrated enhanced third-harmonic generation in Au/CuS heterostructures using harmonically coupled LSPRs.
• Extending nonlinear enhancement to higher harmonics requires incorporating materials with higher-frequency harmonic resonances.

Purpose of the Study:

• To report the first observation of enhanced cascaded fourth- and fifth-harmonic generation.
• To investigate the role of coupled LSPRs in Al/Au/CuS heterostructures for higher harmonic generation.
• To develop an analytical model explaining the observed nonlinear enhancements.

Main Methods:

• Fabrication of Al/Au/CuS dual heterostructures.
• Experimental measurement of nonlinear optical responses, specifically fourth- and fifth-harmonic generation.
• Development and application of an analytical model based on incoherent dipole-dipole interactions.

Main Results:

• Observed enhanced cascaded fourth- and fifth-harmonic generation in Al/Au/CuS driven by coupled LSPRs.
• Coupled LSPRs at fundamental (1050 nm), second harmonic (525 nm), and third harmonic (350 nm) frequencies were identified as key.
• An analytical model accurately accounted for the observed nonlinear enhancements.

Conclusions:

• Al/Au/CuS heterostructures enable efficient generation of higher harmonics through multiple sum-frequency cascades.
• Coupled LSPRs in carefully designed plasmonic structures offer a novel pathway for advanced nonlinear optics.
• This work provides a new design strategy for efficient higher harmonic generation in resonant plasmonic systems.