Terahertz Selective Emission Enhancement from a Metasurface-Coupled Photoconductive Emitter in Quasi-Near-Field Zone
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We present a THz emission enhancement of 41 times at 0.92 THz from a metasurface made of T-shaped resonators excited in a quasi-near-field zone. Such a metasurface has an intrinsic transmission minimum with Q factor of 4 at 1.25 THz under far-field excitation. When this metasurface is coupled onto the backside of a 625-μm-thick photoconductive emitter, the metasurface is below the Fraunhofer distance to the excitation source. As such, one broad enhancement around 0.47 THz and another extremely narrow enhancement at 0.92 THz in the emission spectrum are observed owing to a quasi-near-field excitation. Theoretically, the Q factor of the latter is up to 307, which is limited by the spectral resolution in experiment. The numerical simulations indicate that the T-shaped resonators serve as an array of plasmonic antennas resulting in the aforementioned emission enhancement of THz radiation.
KeywordsMetamaterial Quality factor Terahertz Quasi-near-field
The authors acknowledge the contribution of Matthias Ulrich and Niklaus Jaussi for sample fabrication.
This work is financially supported by the Joint Research Fund in Astronomy (U1631112) under the cooperative agreement between the National Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS), and the Swiss National Science Foundation (SNSF# 200020_165686). Zhenyu Zhao acknowledges the Swiss National Science Foundation International Short Visit Program (IZK0Z2_173458).
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