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L1.09 - Engineered Infrared Plasmonic Metamaterials for Molecular Vibration Enhancement and Suppression Observed by Photothermal Spectral-Microscopy 
December 1, 2014   11:30am - 11:45am

Recently, the interaction between plasmonic metamaterials and vibrational modes of a molecule has been studied as a potential method for ultrasensitive light-matter interaction. It has been shown that coupling of radiative modes of plasmonic metamaterials can mimic electromagnetically induced transparency behavior as observed in atomic and molecular interference effects. In this work, we demonstrate coupling between a narrow molecular vibrational mode with a broad plasmonic resonance that enhances or suppresses the molecular resonance. At critical coupling it cancels out the absorption band entirely. The observed phenomenon is investigated by direct absorption using the FTIR and photothermal spectral-microscopy. Plasmonic metamaterials were fabricated using a liftoff process and e-beam lithography. A thin layer of liquid crystal was placed on top of the structures with a weak combinational band at 1912cm-1. By tuning the length and the periodicity of the plasmonic nano-antennae array we were able to suppress, enhance and cancel out the molecular vibrational mode. A home-built mid-IR photothermal setup is used in combination with a tunable QCL, a plasmonic substrate, an inexpensive silicon photodetector and lock-in detection to measure the sensitivity and specificity of performing vibrational infrared spectroscopy on biomolecules. Mid-IR photothermal spectroscopy combined with plasmonic metamaterials has the potential to detect ultralow concentration of absorbers using low-cost photodetectors and bright tunable QCLs.

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