Terahertz metasurface for near-field beam conversion

Area of Science:

• Optics and Photonics
• Terahertz Technology

Background:

• Uniform illumination is critical for effective terahertz imaging.
• Conventional Gaussian to flattop beam conversion methods often involve complex, bulky lens systems operating in the far-field.

Purpose of the Study:

• To develop a compact and efficient method for converting quasi-Gaussian beams to flattop beams using a single metasurface lens.
• To enable efficient beam shaping in the near-field for terahertz applications.

Main Methods:

• A single metasurface lens was designed to convert a quasi-Gaussian beam from a WR-3.4 horn antenna's near-field to a flattop beam.
• The design process was optimized by dividing it into three stages to reduce simulation time.
• The Gerchberg-Saxton algorithm was combined with the Kirchhoff-Fresnel diffraction equation.

Main Results:

• Experimental validation demonstrated the successful conversion of a quasi-Gaussian beam to a flattop beam at 275 GHz.
• A high conversion efficiency of 80% was achieved.
• The metasurface lens operated effectively in the near-field region.

Conclusions:

• A single metasurface lens provides an efficient solution for Gaussian to flattop beam conversion in the near-field.
• The demonstrated technique is highly efficient and suitable for practical terahertz imaging systems.
• The design methodology is applicable to general near-field beam shaping tasks.