Bound States in the Continuum in Dielectric and Plasmonic Metasurfaces: From Optofluidics to Thermal Emission Engineering

Recently, the concept of bound states in the continuum (BICs) has emerged as a promising approach to achieve sharp spectral resonances and strong electromagnetic field enhancements in plasmonic and dielectric metasurfaces. BICs represent eigenmodes that exist above the light cone but remain decoupled from the radiation continuum of free space. While true BICs, are completely invisible in the radiation spectrum and inaccessible, perturbations can lead to quasi-BIC modes characterized by a sharp spectrum peak and a finite quality factor (Q). In the first part of my talk, I will discuss the utilization of quasi-BIC modes to enable optofluidic control in all-dielectric metasurfaces. By exciting BIC modes, we can significantly enhance the speed of particle transport and assembly. The high-Q nature of quasi-BICs allows for precise tuning of particle assembly by adjusting the wavelength within a narrow spectral range. This enhanced optofluidic control enabled by quasi-BICs holds great potential for lab-on-chip applications, including analyte enrichment for sensing, on-chip mixing, and reconfigurable optically-active colloidal assembly. Moving on to the second part of my talk, I will introduce the use of plasmonic quasi-BICs for engineering thermal emission. Additionally, I will present a slotted quasi-BIC metasurface design that further enhances the quality factor of thermal quasi-BIC metasurfaces. Our numerical simulations demonstrate an ultra-narrowband emission peak with a Q factor of approximately 64 and near-unity absorptance over a broad band spanning more than 10 μm. By symmetrically introducing air slots, the Q factor can be further increased to around 100. Importantly, our experimental measurements confirm the remarkable stability of the resonance frequency in the face of temperature fluctuations. This research showcases the potential of plasmonic quasi-BICs in the design of ultra-narrowband thermal emitters that remain insensitive to temperature changes in the mid-infrared range. Furthermore, this concept can be readily adapted to other frequency ranges, such as near-infrared, Terahertz, and Gigahertz.