Ultrathin freestanding terahertz vector beam generators with free phase modulation

Area of Science:

• Optics and Photonics
• Metamaterials
• Terahertz Technology

Background:

• Simultaneous control of phase and polarization is crucial for tailoring beam properties, enabling structured beams like vector and vector vortex beams.
• Metasurfaces offer a promising platform for manipulating light properties due to their subwavelength structures.
• Terahertz (THz) frequency range presents unique opportunities for novel applications in imaging, sensing, and communication.

Purpose of the Study:

• To propose and demonstrate an ultrathin freestanding metasurface for efficient generation of vector vortex beams at terahertz frequencies.
• To achieve arbitrary topological charge control from linearly polarized excitation.
• To enable the development of compact and versatile terahertz systems.

Main Methods:

• Design of an ultrathin freestanding metasurface composed of bilayer metallic patterns separated by a quartz slab.
• Utilizing a tightly cascaded two-layer structure to form a Fabry-Perot cavity for enhanced polarization and phase control.
• Fabrication and experimental testing of two metasurfaces at 0.14 THz for generating radially polarized vector beams with uniform and vortex phases.

Main Results:

• Successful demonstration of efficient generation of high-quality vector beams with desired phase properties.
• Experimental validation of the metasurface's capability to produce vector vortex beams with arbitrarily defined topological charges.
• Confirmation of the ultrathin and freestanding nature of the metasurface, facilitating integration with other optical components.

Conclusions:

• The proposed ultrathin metasurface provides an efficient method for generating terahertz vector vortex beams with precise control over phase and polarization.
• The device's design, leveraging a Fabry-Perot cavity, maximizes efficiency in manipulating beam properties.
• The demonstrated capabilities and ease of integration highlight the significant potential of this metasurface for compact terahertz systems and future optical applications.