Design of metalens with local phase control for high power THz emission

Spintronic terahertz emitters (STEs) are novel sources capable of emitting radiation in a wide THz frequency band. They, however, suffer from low efficiency and emitted power. To increase their power, we have proposed in this work the possibility of integrating a focusing metasurface (metalens) directly on top of the STE substrate backside. The feasibility of this metasurface is achieved with the generalized Snell’s law and the non-resonant propagation phase mechanism. The proposed basic unit cell of the metasurface is a high aspect ratio cylinder made of poly(methyl methacrylate) (PMMA) resist, which is producible simply by the initial steps of the LiGA (lithography, electroplating, molding) process. These structures are designed and optimized using simulations in the commercial software CST Microwave Studio with the frequency and time domain solvers. Simulation results are compared to those obtained with analytical relations from diffraction theory, which allows easier calculation for large-scale problems.