Nonlinear Terahertz Absorption of Graphene Plasmons

Area of Science:

• Plasmonics
• Nonlinear Optics
• Terahertz Spectroscopy

Background:

• Subwavelength graphene structures exhibit localized plasmonic resonances.
• Strong field confinement enhances light-graphene interactions, enabling low-intensity nonlinear optics.
• Experimental studies on graphene plasmon nonlinear response and energy loss dynamics are lacking.

Purpose of the Study:

• To experimentally investigate the terahertz nonlinear response of graphene plasmons.
• To study the energy relaxation dynamics of plasmons in graphene nanoribbons.
• To theoretically model the observed nonlinear phenomena.

Main Methods:

• Terahertz pump-terahertz probe spectroscopy at the plasmon frequency.
• Fabrication and characterization of graphene nanoribbons.
• Theoretical modeling of nonlinear plasmonic absorption and electron temperature effects.

Main Results:

• Observed strong saturation of plasmon absorption in graphene nanoribbons.
• Measured a 10 ps relaxation time for plasmon energy loss.
• Demonstrated a 2 orders of magnitude enhancement in nonlinearity compared to unpatterned graphene.
• Developed a thermal model explaining the red shift and resonance changes due to electron temperature.

Conclusions:

• Graphene nanoribbons exhibit significantly enhanced nonlinear optical responses.
• Transient electron temperature plays a crucial role in the observed nonlinear plasmonic absorption.
• High-mobility graphene could further boost nonlinear effects, promising for optical processing applications.