Second harmonic generation based on strong field enhancement in nanostructured THz materials

Area of Science:

• Terahertz (THz) science and technology
• Plasmonics and metamaterials
• Nanophotonics

Background:

• Terahertz (THz) radiation applications are limited by weak interactions with materials.
• Subwavelength structures offer field enhancement for improved THz interactions.
• Split-ring resonators (SRRs) and nanoslits are promising candidates for THz field manipulation.

Purpose of the Study:

• To numerically investigate the terahertz (THz) response of micro/nanoscale slit structures and split-ring resonators (SRRs).
• To explore the field enhancement mechanisms in these nanostructures.
• To demonstrate the utility of these structures in nonlinear THz experiments.

Main Methods:

• Numerical simulations of THz wave interaction with slit structures and SRRs.
• Analysis of light-induced current flows and capacitive charging.
• Experimental demonstration of second harmonic generation (SHG) using nonlinear substrates and nanostructures.

Main Results:

• Both structures show significant field enhancement in the gap region.
• Nanoslits provide broadband enhancement, while SRRs offer narrowband amplification.
• SRRs achieve field enhancement factors in the tens of thousands.
• Nanostructure placement on nonlinear substrates significantly boosts frequency-doubled signal generation.

Conclusions:

• SRRs are highly effective for nonlinear THz applications due to strong, narrowband field enhancement.
• Nanostructure integration enhances nonlinear optical processes like second harmonic generation.
• These findings pave the way for advanced nonlinear THz spectroscopy and applications.