Adiabatic Frequency Conversion Using a Time-Varying Epsilon-Near-Zero Metasurface.

Area of Science:

• Optics and Photonics
• Materials Science
• Nonlinear Optics

Background:

• Time-dependent changes in a material's refractive index alter the frequency of transmitted optical beams.
• Adiabatic frequency conversion (AFC) is a phenomenon where optical beam frequency changes due to a time-varying refractive index.
• Epsilon-near-zero (ENZ) materials exhibit unique electromagnetic properties near their plasma frequency.

Purpose of the Study:

• To experimentally demonstrate enhanced adiabatic frequency conversion (AFC) using nonlinear epsilon-near-zero (ENZ) plasmonic metasurfaces.
• To investigate the tunability and bandwidth of the frequency shift achieved.
• To compare the performance of ENZ-based metasurfaces with traditional ENZ materials for AFC.

Main Methods:

• Fabrication of a 63-nm-thick nonlinear ENZ-based plasmonic metasurface.
• Experimental setup to induce and measure adiabatic frequency conversion using the metasurface.
• Characterization of frequency shift magnitude, tunability, and bandwidth under varying pump intensities.

Main Results:

• A large, tunable, and broadband frequency shift of up to ~11.2 THz was achieved with a pump intensity of 4 GW/cm².
• The metasurface demonstrated a ~10-fold decrease in device thickness compared to bare ENZ materials.
• A ~120-fold reduction in pump peak intensity was observed for a similar frequency shift compared to bulk ENZ materials.

Conclusions:

• Nonlinear ENZ-based plasmonic metasurfaces significantly enhance adiabatic frequency conversion.
• These metasurfaces offer a highly efficient and compact platform for manipulating optical beam frequencies.
• The findings provide a foundation for designing advanced time-varying metasurfaces for ultrafast pulse manipulation.