Sparse‐Aperture Quasi‐Achromatic Spintronic Terahertz Emitter Enabled by Binary‐Phase Metasurface and Multi‐Spectral Intensity Optimization

Terahertz (THz) technology exhibits enormous potential application in imaging and next‐generation communications. However, the lacking of compact broadband THz sources capable with focusing and wavefront manipulation capabilities remains a significant challenge for its practical application. To address this, we propose a design paradigm that combines a sparse‐aperture shared‐aperture architecture with a multispectral weighted intensity optimization method, enabling the direct construction of a Pt/W binary‐phase metasurface on a spintronic terahertz emitter. The device has an overall aperture of 2 cm and features three groups of centrosymmetric sector‐shaped sub‐apertures, each group individually optimized for specific sub‐bands. Numerical results demonstrate that the device achieves broadband quasi‐achromatic focusing over the continuous 1.0–1.5 THz band, characterized by overlapping depth‐of‐focus ranges and stabilized focal‐spot intensity at a common design plane. The spectral intensity fluctuation is suppressed to below 33%. Meanwhile, at all representative frequencies, the edge preservation index remains above 0.68, verifying the robust broadband focusing performance. This work establishes a new paradigm for active terahertz metasurface design and provides a viable pathway toward compact, efficient, and quasi‐achromatic integrated photonic systems for advanced imaging and communication applications.