Highly efficient compact and narrowband plasmonic absorber design using dense/sparse epsilon-near-zero spherical shell arrays

• Published in: Optics and laser technology Vol. 175; p. 110796
• Main Authors: Raad, Shiva Hayati, Afshari-Bavil, Mehdi, Liu, Dong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2024
• Subjects: Absorption efficiency; ENZ; Graphene; Narrowband absorber; Particle array; ENZ; Particle array; Graphene; Narrowband absorber; Absorption efficiency
• ISSN: 0030-3992; 1879-2545
• DOI: 10.1016/j.optlastec.2024.110796

In this paper, epsilon-near-zero (ENZ) plasmonic resonances of graphene material are employed to design efficient, compact, and narrowband optical absorbers. These resonances occur around the negative to positive permittivity transition frequencies. The geometry under consideration is hollow-core graphene shell spherical particles assembled as dense and sparse square arrays. It is observed that, unlike the ordinary plasmonic graphene-based nano-particle-assisted absorbers, an increase of the core radius blue shifts the operating resonance frequency. The underlying physics is discussed based on the resonant scattering condition in the metal shell dielectric particles in the framework of Mie’s theory. Based on this observation, the smaller particles are found to be more efficient optical absorbers in the ENZ regime due to their small geometrical and scattering cross-sections. Then, a comprehensive parametric study is conducted considering graphene optical parameters and the possibility of absorption enhancement based on the available graphene material quality is revealed. The tunability of the absorption spectrum by applying an external bias is also discussed. The proposed shells can be potentially used as a high figure of merit refractive index sensing medium and also for enhancing the radiation of the dipole emitter. Furthermore, using a metal-backed dielectric reflector, perfect absorbers with high-quality factors are achieved with both dense (Q ∼ 620.43) and sparse (Q ∼ 3019.9) arrays in the subwavelength regime. The proposed polarization-insensitive absorber tolerates a wide range of incident angles up to around 60 degrees due to its spherical symmetry.