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

This Letter describes a super-oscillatory lens (SOL), with concentric ring-type metallic slits photolithographically fabricated on a glass substrate, that can function at subterahertz frequencies. The SOL has been investigated both experimentally and theoretically and demonstrates a spatial resolution of 1.5 mm ( 0.5 λ ), which is 0.45 times the diffraction limit, with a focal length of 75 mm ( 25 λ ) at 100 GHz ( λ = 3 m m ). Furthermore, the depth of focus of the lens was measured to be 47 mm, which is 10.8 times larger than that of a conventional lens. This type of SOL, with subdiffraction focusing, is thus highly effective for use in industrial inspections with millimeter and terahertz waves.