Investigation and application of the plasmonic enhancement effect from inverse plasmonic nanostructures on chiral light-matter interaction

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Within the proposal “Investigation and application of the plasmonic enhancement effect from inverse plasmonic nanostructures on chiral light-matter interaction” we plan to understand and make use of plasmonic structures to amplify chiral light-matter interactions in the mid infrared spectral range with the vision of being able to determine and investigate the chirality of minute amounts of samples by employing cost effective instruments.The research proposal aims at addressing two different questions in two scenarios which are mutually interconnect. In the first scenario, chiral excitation and chiral nanostructures are used to enhance the CD response of chiral molecules. We have already proved by experiment that based on this scenario the differentiation of enantiomers is possible, but so far an explanation for the working principle based on theory is not possible. For this part, we will carry out comprehensive and systematic investigations of the dependence of the enhancement effects on the plasmonic structures by varying them systematically. The results will be used as input for the second scenario.In the second scenario, linearly polarized excitation and an achiral substrate consisting of elliptical nanopores in a gold film will be used to enhance the circular dichroism of chiral molecules. This approach has the advantage that the chiral optical field is only generated locally in the near field of the nanostructure. Therefore, a working structure would have three benefits. First, linearly polarized excitation greatly reduces the cost of the experimental setup because no expensive VCD spectrometers with photoelastic modulators are needed. Secondly, linearly polarized illumination allows the combination of VCD with optical microscopes, enabling spatially resolved micro-VCD analysis. Finally, using linearly polarized illumination and achiral substrates provides a background-free detection of the VCD signals from the molecules as neither molecules outside of the hot zone nor the plasmonic structure will contribute to the signal. Accordingly, we will investigate the circular dichroism of chiral molecules by evaluating the transmission signal from elliptical nanopores filled with analyte in an extended gold film. The intended experiments will also allow to determine if this is indeed the best scenario for plasmon-enhanced circular dichroism spectroscopy. If successful, the study will lead to a simple and effective platform for ultrasensitive chiral analysis.