Terahertz tight-focused Bessel beam generation and point-to-point focusing based on nonlocal diffraction engineering

Area of Science:

• Optics and Photonics
• Metamaterials and Nanophotonics
• Terahertz (THz) Technology

Background:

• Metasurfaces control light wavefronts by spatially modulating amplitude or phase.
• Traditional unit-cell designs face limitations with large spatial gradients.
• Supercell structures offer an alternative for advanced wavefront engineering.

Purpose of the Study:

• To demonstrate metasurfaces utilizing supercell structures for terahertz applications.
• To achieve plane wave-to-Bessel beam transformation and point-to-point focusing.
• To validate the performance of supercell-based metasurfaces through simulations and experiments.

Main Methods:

• Diffraction engineering of supercell structures for metasurface design.
• Application of supercell metasurfaces for terahertz beam manipulation.
• Numerical simulations and experimental validation of device performance.

Main Results:

• Achieved efficient plane wave-to-Bessel beam transformation with a small beam waist (0.57λ) and long depth of focus (9.1λ).
• Demonstrated point-to-point focusing, altering the divergence angle from 16° to 70°.
• Validated metasurface performance through numerical simulations and experimental results with good agreement.

Conclusions:

• Supercell structures provide a superior method for metasurface wavefront control, especially for large spatial gradients.
• The developed metasurfaces enable novel applications in terahertz imaging and beam manipulation.
• This approach advances the capabilities of terahertz optical devices.