Chiral metasurface absorber with near-infrared excitation-induced dual circular dichroism

Microscopic components in metasurfaces allow precise control of electromagnetic waves, enabling chiral metasurface absorbers to adapt to different frequencies and wavelengths of electromagnetic waves, providing higher controllability. In this paper, we present a near-infrared chiral absorber utilizing a Metal-Insulator-Metal (MIM) structure, achieving selective absorption in the dual wavelength ranges of 1500–1750 nm and 2250–2750 nm. The absorber's structural layout adopts a pseudo-π configuration, featuring a unique design that establishes distinct resonance cavities between structural periods. This results in disparate responses to left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, thereby attaining dual-band selectivity and adjustability. To illustrate the physical mechanism, we explore the electric and magnetic field distributions within this structure, offering deeper insights into the fundamental mechanism of selective absorption. This analysis illustrates that the charge distribution in different wavelength bands can vary with the polarization direction, forming orthogonal electric dipoles. Under the incidence of LCP and RCP, we achieved circular dichroism (CD) of 0.75 and 0.7, respectively. By adjusting parameters within individual resonance cavities, we achieve independent control over each resonance wavelength. This near-infrared chiral absorber provides unparalleled design flexibility, with implications for advancements in applications such as molecular detection and optical switching.