Figure 3 |. Polarization-multiplexed multi-resonant broadband plasmonic metasurface.

a, Photograph and SEM image of the two-dimensional array of plasmonic ulu nanostructures. The geometrical design parameters for the structure in the SEM image are $P_x=3.2\text{μm}$, $P_y=3.2\text{μm}$, $L_1=2.4\text{μm}$, $L_2=0.95\text{μm}$, $L_3=0.8\text{μm}$, $g=0.14\text{μm}$, and $w=0.14\text{μm}$; 90 nm thick. b, Numerically simulated electric near-field intensity enhancement ${\left|E/E_0\right|}^2$ maps at different resonance wavenumbers for 0$°$ and 90$°$ polarizations. c, d, Experimentally measured (black curves) and simulated (red-yellow gradient) reflectance spectra of the polarization-multiplexed multi-resonant plasmonic metasurface. The three resonant peaks are tuned by adjusting the geometrical parameters of the ulu structures, such as $L_1$, $L_2$, and $L_3$, to spectrally match the absorption fingerprints of important biomolecules in the mid-Infrared region. e, f, Simulated reflectance spectra shows expected absorption signals associated with the molecular fingerprints of deoxyribose (1060 cm⁻¹ ▲), asymmetric phosphate (1236 cm⁻¹ ▲), $\text{β}$-sheet (1542 cm⁻¹ ▲), amide II (1574 cm⁻¹ ▲), amide I (1660 cm⁻¹ ▲). Molecular coupling with plasmonically enhanced near-field hotspots at the resonance peaks (black dashed line) leads to dips in reflection spectra at wavenumbers corresponding to the vibrational resonances of the biomolecules (solid line).