Subdiffraction focusing with a long focal length using a terahertz-wave super-oscillatory lens

Area of Science:

• Optics and Photonics
• Electromagnetics
• Materials Science

Background:

• Conventional lenses are limited by the diffraction limit, restricting spatial resolution.
• Subterahertz frequencies are increasingly important for advanced imaging and sensing applications.
• Super-oscillatory phenomena offer a route to overcome diffraction limitations.

Purpose of the Study:

• To design and experimentally validate a super-oscillatory lens (SOL) operating at subterahertz frequencies.
• To demonstrate sub-diffraction focusing capabilities of the SOL.
• To evaluate the SOL's performance metrics, including spatial resolution and depth of focus.

Main Methods:

• Photolithographic fabrication of a super-oscillatory lens with concentric metallic slits on a glass substrate.
• Experimental characterization of the SOL at 100 GHz.
• Theoretical analysis to complement experimental findings.

Main Results:

• Achieved a spatial resolution of 1.5 mm (0.5λ), which is 0.45 times the diffraction limit.
• Demonstrated a focal length of 75 mm (25λ) at 100 GHz (λ=3mm).
• Measured a depth of focus of 47 mm, 10.8 times larger than conventional lenses.

Conclusions:

• The developed SOL effectively achieves sub-diffraction focusing at subterahertz frequencies.
• The SOL's superior spatial resolution and extended depth of focus are highly beneficial.
• This technology shows significant promise for industrial inspections using millimeter and terahertz waves.