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Maximizing the electromagnetic efficiency of spintronic terahertz emitters
preprintposted on 2024-02-10, 17:00 authored by Pierre Koleják, Geoffrey Lezier, Daniel Vala, Baptiste Mathmann, Lukáš Halagačka, Zuzana Gelnárová, Yannick Dusch, Jean-François Lampin, Nicolas Tiercelin, Kamil Postava, Mathias Vanwolleghem
Spintronic Terahertz Emitters (STE) represent a significant advancement in source technology, exploiting the ultrafast demagnetization process of spin-electrons to unveil a 30THz wide, gapless spectrum, accessible through femtosecond lasers across the full VIS-IR range. This innovation not only positions STEs as a pivotal advancement in THz source technology but also underscores their role as a cost-effective, high-performance solution, thereby redefining standards within the field. However, the inherent spintronic nature of these devices introduces a challenge: a lower optical-to-terahertz conversion efficiency, which positions them at a notable disadvantage relative to other sources. In response, this work aims to substantially improve the electromagnetic efficiency of these emitters. This is accomplished by maximizing the energy conversion from the pumping laser for spin-electron generation. Our design integrates STEs with an optimized 1D trapping cavity, specifically engineered to fulfill critical aspects of ultrafast excitation and THz extraction. As a result, we have realized a 245% enhancement in emission and an increase of 8dB in overall intensity, positions our results among the most substantial improvements documented in this field. Furthermore, we delineate the optimal geometry for the deployment of STEs and explore the strategic selection of substrates in depth. Such enhanced emitters advance spintronic emitters towards broader applications in time-domain spectroscopy, ellipsometry, and nonlinear THz-pump spectroscopy. Enhancing spintronic emitter efficiency, combined with rapid magnetic field modulation, indicates the potential for dynamic ranges that rival traditional sources. Our predictions of STE's efficiencies, made through an electromagnetic approach, highlight its capability to uncover overlooked aspects from an optical standpoint, leading to subsequent improvements.