While standard surface plasmon resonance (bio) sensing, relaying on propagating surface plasmon polariton sensitivity on homogeneous metal/dielectric boundaries, represents nowadays a routine sensing technique, other alternatives, such as inverse designs with nanostructured plasmonic periodic hole arrays, have been far less studied, especially in the context of gas sensing applications. Here, we present a specific application of such a plasmonic nanostructured array for ammonia gas sensing, based on a combination of fiber optics, extraordinary optical transmission (EOT) effect, and chemo-optical transducer selectively sensitive to ammonia gas. The nanostructured array of holes is drilled in a thin plasmonic gold layer by means of focused ion beam technique. The structure is covered by chemo-optical transducer layer showing selective spectral sensitivity towards gaseous ammonia. Metallic complex of 5-(4′-dialkylamino-phenylimino)-quinoline-8-one dye soaked in polydimethylsiloxane (PDMS) matrix is used in place of the transducer. Spectral transmission of the resulting structure and its changes under exposition to ammonia gas of various concentrations is then interrogated by fiber optics tools. The observed VIS-NIR EOT spectra are juxtaposed to the predictions performed by the rigorous Fourier modal method (FMM), providing useful theoretical feedback to the experimental data, and ammonia gas sensing mechanism of the whole EOT system and its parameters are discussed.

In accordance with growing scientific interests in nanoplasmonic structures, along with the increasing ability to fabricate them using proper nanotechnologies, we have developed a methodology to incorporate nonlocal optical responses, described with a simple hydrodynamic model, into the numerical Fourier modal method (FMM) technique to enable broadening of the simulation portfolio of such physical phenomena in plasmonic nanostructures. Here, we have newly incorporated the nonlocal response approximation (NRA) into the periodic FMM technique (called NonLocFMM) described with a proper hydrodynamic model, and we show in several examples that this implementation is capable of numerically analyzing periodic plasmonic systems, such as nonlocal periodic multilayers and resonant gratings. The implementation was performed in such a way that a future possible generalization of the hydrodynamic nonlocal description will be feasible, as well as the aperiodization of the technique. Such an extension is, indeed, viable and will be the subject of a subsequent paper.

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