Exploiting hyperbolic metamaterial as a substrate for graphene surface plasmonic Cherenkov THz radiation source
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Exploiting hyperbolic metamaterial as a substrate for graphene surface plasmonic Cherenkov THz radiation source Nalini Pareek1,2 · Niladri Sarkar3 · Anirban Bera1,2 Received: 12 July 2020 / Accepted: 8 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this work, a graphene-dielectric multilayer hyperbolic metamaterial (GHMM) has been analyzed for the generation of THz Cherenkov radiation (CR) from graphene surface plasmonics (GSP), induced by a moving electron bunch. The structure under analysis consists of a graphene-dielectric multilayer HMM in which the top graphene layer is considered as an interface between air and the underlying multilayer as the substrate. The dispersion analysis of the structure shows the existence of bulk-HMM (BH) and non-bulk HMM (NBH)-region in the 𝜔–k space. The structure is found to generate intense CR from the GSP, when the operating point of the electron bunch lies in the BH-region, as the bulk states of the HMM substrate allows the efficient transformation of high-k GSP into THz-CR. The proposed structure can be exploited as a potential candidate for the development of low-voltage, electron beam-driven, ultra-tunable, compact graphene plasmonic Cherenkov THz radiation source. Moreover, the application of the principle of utilizing bulk states of HMM for CR generation has also been discussed for black phosphorous (BP), an emerging 2Dmaterial for the THz to infrared (IR) region.
1 Introduction THz radiation sources have been an integral part of many scientific experiments since the inception of THz Science and continue to be of importance as these radiations are promising candidates for many applications [1]. However, the unavailability of THz sources with characteristics such as high intensity and tunability, and which can operate at low operating voltage, remains an issue. To realize a compact THz source with the desired characteristics it has been suggested to introduce photonic concepts such as the use of photonic crystals, plasmonics, and metamaterials in the field of vacuum electronic devices [2, 3]. Recently, graphene has been identified as a two-dimensional (2D) material that extends the applicability of the photonic concepts to the THz band as it supports collective oscillation in this band of the electromagnetic spectrum [4]. * Nalini Pareek [email protected] 1
CSIR-Central Electronics Engineering Research Institute, Pilani 333031, India
2
Academy of Scientific and Innovative Research, New Delhi, India
3
Birla Institute of Technology & Science, Pilani, Rajasthan 333031, India
Moreover, graphene surface plasmon (GSP) can be electrostatically tuned in the THz range and show higher confinement and offer higher light–matter interaction [5], making graphene a preferred alternative to traditional metal plasmonics [6]. Further, GSP shows a slower decaying process of plasmon as compared to conventional plasmonic platforms based on noble metals [7]. These properties make graphene an attractive choice for various applications, some
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