Subdiffraction focusing with a long focal length using a terahertz-wave super-oscillatory lens
Ayato Iba, C. W. Domier, Makoto Ikeda, A. Mase, Makoto Nakajima, Anh‐Vu Pham, Neville C. Luhmann
Abstract
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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>0.5</mml:mn> <mml:mi>λ</mml:mi> </mml:math> ), which is 0.45 times the diffraction limit, with a focal length of 75 mm ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>25</mml:mn> <mml:mi>λ</mml:mi> </mml:math> ) at 100 GHz ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:math> ). 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.