Realizing a terahertz far-field sub-diffraction optical needle with sub-wavelength concentric ring structure array

Area of Science:

• Optics and Photonics
• Terahertz (THz) Technology

Background:

• Conventional terahertz (THz) lenses are limited by the diffraction limit, restricting resolution in THz optical systems.
• Optical super-oscillation offers a method to generate sub-diffraction focal spots, improving microscopic imaging resolution in the visible spectrum.
• Demonstrations of THz lenses utilizing super-oscillation for sub-diffraction focusing remain scarce.

Purpose of the Study:

• To propose and experimentally demonstrate a planar lens capable of far-field sub-diffraction focusing in the terahertz range.
• To overcome the resolution limitations of conventional THz lenses through super-oscillation principles.
• To investigate the potential of super-oscillation for creating sub-diffraction focal spots (hotspots or needles) in THz imaging.

Main Methods:

• Design and fabrication of a planar lens composed of a sub-wavelength concentric ring structure array.
• Utilizing silicon-etching processes for precise lens fabrication.
• Experimental characterization of the lens's focusing capabilities at a wavelength of 118.8 μm.

Main Results:

• The fabricated planar lens successfully generated a sub-diffraction optical needle with a length of 19.7λ along the optic axis.
• The smallest achieved focal spot exhibited a transverse size of 1.212λ, which is below the diffraction limit of 1.476λ.
• The lens demonstrated effective sub-diffraction focusing, surpassing the capabilities of traditional THz lenses.

Conclusions:

• The proposed sub-diffraction optical needle planar lens is a viable alternative to conventional THz lenses.
• This technology holds significant potential for advancing super-resolution tomography THz imaging systems.
• The successful demonstration paves the way for next-generation THz imaging with enhanced resolution.