High-performance Reflective Focusing of Terahertz Beams Using Holographic Metasurfaces

The terahertz (THz) band of the electromagnetic spectrum is conveniently sandwiched between the microwave and infrared regions that allows one to combine both optical and microwave techniques in THz instrumentation and to synthesize unique instrumental solutions. Such a synthesis is proven to be very effective when planar metallized microstructures of subwavelength topology, commonly referred to as frequency selective surfaces (FSSs) or measurfaces (metaFSS), are used for manipulating amplitude, polarization and phase characteristics of quasi-optical THz beams. In microwave engineering, the phase control is of great importance in the technology of low-profile reflectarray antennas, whose conventional design implies exploiting a grounded-dielectric-slab-backed FSS with spatial-depended reflection phase. Transferred to the THz band, this approach is estimated to be promising for beam-shaping and beam-focusing techniques as it allows creating purely flat, thin and lightweight reflectors capable of properly manipulating the wavefront through the control of the FSS unit cell geometry. Due to relative simplicity in photolithographic fabrication, such kind of reflectors serve as an attractive alternative to the conventional diffractive optical elements (DOEs) based on cost-consuming structures with profiled surfaces.