Realizing high-efficiency third harmonic generation via accidental bound states in the continuum.

Area of Science:

• Metasurface optics
• Nonlinear optics
• Quantum optics

Background:

• Bound states in the continuum (BICs) offer high Q-factors and minimal radiative loss, making them valuable for optical device design.
• Metasurfaces are engineered structures that manipulate light at the nanoscale.

Purpose of the Study:

• To demonstrate third harmonic generation (THG) at a near-ultraviolet wavelength (343 nm) using accidental BICs in a metasurface.
• To achieve high nonlinear conversion efficiency with a simple metasurface structure.

Main Methods:

• Fabrication of a metasurface designed to support accidental BICs.
• Experimental setup for measuring third harmonic generation (THG) under near-ultraviolet light excitation.
• Characterization of the nonlinear conversion efficiency at various pump intensities.

Main Results:

• Realization of THG at 343 nm through accidental BICs in the metasurface.
• Achieved an absolute conversion efficiency of 1.13 × 10^-5 for THG.
• Obtained this high efficiency at a relatively low peak pump intensity of 0.7 GW/cm².

Conclusions:

• Accidental BICs in metasurfaces provide an effective platform for efficient nonlinear frequency conversion.
• The demonstrated approach offers a simple yet powerful method for generating high nonlinear conversion efficiencies.
• This work paves the way for novel applications in nonlinear optics and photonic devices.