Quantification of Multiple Molecular Fingerprints by Dual‐Resonant Perfect Absorber

A dual‐resonant perfect absorber (PA) based on multiple dipolar nanoantenna configuration is introduced. The PA platform exhibits near‐unity (95%–98%) absorbance in dual‐resonances. A fine‐tuning mechanism of dual‐resonances is determined via geometrical device parameters of the constituting dipolar elements of the compact PA system. It is also shown that the dual plasmonic resonances are associated with easily accessible and large local electromagnetic fields. Possessing large absorbance with strong nearfields, the PA system is highly advantageous for surface enhanced infrared absorption (SEIRA) spectroscopy applications. The simultaneous detection of absorption signals corresponding to C=O and C–H bands of a polymethyl methacrylate (PMMA) film, which are separated by as large as ≈1255 cm⁻¹, is experimentally shown. Furthermore, the interaction between plasmonic modes of the PA platform and the molecular vibrational modes of the PMMA film is investigated by tuning the optical resonances within the C=O spectral window. The coupling strength between plasmonic and vibrational modes is determined by Hamilton analysis, which leads to mode splitting and anticrossing behavior within the PA absorption spectra. The PA platform, by enabling simultaneous identification of different molecular fingerprints, can provide more reliable sensing information compared to classical SEIRA systems based only on a single vibrational mode.