Tri-band and one-foci sparse-aperture achromatic spintronic terahertz Fresnel-Zone-Plate emitters by deep learning

Ultrathin spintronic THz emitters (STEs) have shown exceptional advantages across various applications, offering a compelling combination of cost-effectiveness and high performance. However, the functional spin THz devices are still lacking. Here, we propose a tri-band and one-foci sparse-aperture achromatic spintronic terahertz Fresnel-Zone-Plate emitter, and three arbitrarily generated THz band waves are achieved with achromatic performance. More than 20 times enhancement of the focused field intensity is gotten. Furthermore, the structure of the AST-FE is optimized by using a bidirectional Deep Neural Network. The efficiency and amplitude of the generated THz, along with its focusing characteristics, are both enhanced. By integrating this flat-spin THz device with other reported achromatic methods, we can obtain multi-frequency achromatic THz waves easily. This research will promote the study and use of spin THz devices, and make great influence of the THz system.