Quasi-phase matching for efficient long-range plasmonic third-harmonic generation via graphene

Area of Science:

• Nonlinear Optics and Photonics
• Condensed Matter Physics
• Terahertz (THz) Science and Technology

Background:

• Surface plasmon polaritons (SPP) on graphene are crucial for nonlinear plasmonic applications.
• Third-harmonic generation (THG) in the terahertz (THz) gap is challenging due to graphene's absorption loss.
• Existing methods struggle with maintaining high conversion efficiency (CE) over long propagation distances.

Purpose of the Study:

• To propose and numerically investigate an efficient method for long-range THG of SPP waves on graphene.
• To address the limitations of absorption loss in unmodulated graphene for THz nonlinear plasmonics.
• To enhance the conversion efficiency of THG for SPP waves at extended propagation lengths.

Main Methods:

• Development of a nonlinear finite-difference time-domain (FDTD) technique for numerical simulations.
• Investigation of THG of SPP waves on graphene sheets with varying Fermi levels.
• Design and analysis of a periodic graphene structure incorporating low and high Fermi-level regions.

Main Results:

• Unmodulated graphene with low Fermi levels shows high CE for THG at short distances but suffers from significant absorption loss.
• A proposed periodic structure utilizing alternating low and high Fermi-level graphene regions enhances long-range THG efficiency.
• The periodic structure satisfies the quasi-phase matching condition, leading to considerable improvement in CE at longer propagation distances.

Conclusions:

• Periodic modulation of graphene Fermi levels is an effective strategy to overcome absorption losses for long-range SPP THG.
• The proposed structure offers a promising pathway for efficient nonlinear THz plasmonic devices.
• Potential applications include frequency generation, spectroscopy, and signal processing in the THz regime.