Efficient Anomalous Refraction of THz Beams with a Multilayer Metal-Polymer Huygens' Metasurface

We describe design principles, fabrication techniques, and experimental testing for a Huygens' metasurface which deflects a normally incident radiation beam at <inline-formula><tex-math notation="LaTeX">$f\approx 0.172$</tex-math></inline-formula>&#x00A0;THz towards an angle of 52<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> in transmission. The metasurface is comprised of a cascade of five spatially-modulated aluminum impedance sheets photolithographically patterned on 100-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m-thick polypropylene substrates, stacked together via ultrathin adhesive layers. The physical geometries realizing the five-layer Huygens&#x0027; meta-atoms are designed using a semi-analytical model, while the expected deflection, associated with negligible reflection and low diffractive losses, is verified by full-wave simulations and measurements. For the implemented deflector, with a working aperture diameter of 75 mm, the experimentally measured refraction efficiency reached 58&#x0025;, with 20&#x0025; and 22&#x0025; losses attributed to spurious diffraction and absorption, respectively. Despite the suboptimal performance, our results establish the proposed methods of synthesis and fabrication as promising for realizing quasi-optical THz components with unique characteristics, unattainable at this challenging regime with alternative approaches.