Investigation of dual-narrowband plasmonic perfect absorbers at visible frequencies for biosensing

Abstract

Since the introduction of first plasmonic perfect absorber (PA) in early 2008 by Landy et al., numerous studies have demonstrated their superior optical performance in frequencies ranging from terahertz to visible region of electromagnetic spectrum. In the literature broadband PAs are studied in more detail compared to narrowband PAs as their large absorption bandwidths make them a prime candidate for energy harvesting applications or security and defense. Recently scientists have shown a great interest in designing narrowband PAs by controlling the optical losses of the plasmonic materials as the narrowband resonances with a high quality-factor is particularly important for label-free biosensing. However, given the lossy optical properties of metals, this task has been challenging and requires delicate investigation and parameter control in contrast to broadband perfect absorbers. In this research, we numerically studied and experimentally fabricated a narrow-band plasmonic perfect absorber based on a metal-insulator-metal con- figuration. We analyzed the origin of perfect absorption for our proposed system and investigated the parameters that effect the optical properties. The purposed plasmonic structure comes up with a dual narrow-band absorption peaks at visible and near-infrared region of electromagnetic spectrum with near unity absorption e ciency. The physical origin of these absorption peaks is shown to be the excitation of propagating and localized surface plasmon resonances at certain individual frequencies, that leads to impedance matching and critical coupling when certain conditions are satisfied. Finally, we analyzed the sensing capabilities of PA by embedding nanostructure into different background refractive index, resulting in sensitivity of 500 nm/RIU, making such a platform suitable for biosensing and spectroscopic applications. This work analyzes the perfect absorption phenomena in visible frequencies in detail and will be a go to guide for researchers in the perfect absorber community.