Extremely Thin Perfect Absorber by Generalized Multipole Bianisotropic Effect

• Published in: Advanced optical materials 2024-03, Vol.12 (7), p.n/a
• Main Authors: Ma, Hao, Evlyukhin, Andrey B., Miroshnichenko, Andrey E., Zhu, Fengjie, Duan, Siyu, Wu, Jingbo, Zhang, Caihong, Chen, Jian, Jin, Biaobing, Padilla, Willie J., Fan, Kebin
• Format: Article
• Language: English
• Subjects: Absorbers; asymmetric absorption; Broken symmetry; dielectric metasurfaces; Dipoles; Lossless materials; multipole bianisotropy; Multipoles; Quadrupoles; Resonators; Thickness ratio; thin film
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202301968

Symmetry breaking plays a crucial role in understanding the fundamental physics underlying numerous physical phenomena, including the electromagnetic response in resonators, giving rise to intriguing effects such as directional light scattering, supercavity lasing, and topologically protected states. This work demonstrates that adding a small fraction of lossy metal (as low as 1 × 10−6 in volume) to a lossless dielectric resonator breaks inversion symmetry (IS), thereby lifting its degeneracy, leading to a strong bianisotropic response. In the case of the metasurface composed of such resonators, this effect leads to unidirectional perfect absorption while maintaining nearly perfect reflection from the opposite direction. It has developed more general Onsager‐Casimir relations for the polarizabilities of particle arrays, taking into account the contributions of quadrupoles, which shows that bianisotropy is not solely due to dipoles, but also involves high‐order multipoles. The experimental validation demonstrates an extremely thin terahertz‐perfect absorber with a wavelength‐to‐thickness ratio of up to 25,000, where the material thickness is only 2% of the theoretical minimum thickness dictated by the fundamental limit. The findings can pave a new route to design devices for applications involving optical‐to‐heat conversion processes. An asymmetric perfect absorber through breaking the inversion symmetry of a lossless metasurface using extremely thin lossy disks is demonstrated. The disk dissipates almost all of the power, achieving a remarkable volume‐filling fraction at least two orders lower than other highly absorptive films. This strong absorption confinement is attributed to multipole bianisotropy described by general Onsager‐Casimir relations.