Light confinement in the nanoscale regime has opened new doors to the miniaturization of optical materials required for future integrated photonics. Recently, Tamm Plasmons (TP) have attracted research interest as they possess various advantages over conventional surface plasmons. They are characterized by sharp resonances in the transmission spectrum and a low degree of loss, making them ideal and versatile platforms for nonlinear applications. In this work, we report the enhanced nonlinear response of gold@carbon (Au@C) core-shell nanostructures aided by a TP cavity. The spacer layer containing Au@C is sandwiched between gold film and a DBR made of TiO2 and SiO2 layers. The photonic bandgap of the DBR is centered around 534 nm, and the final structure is characterized by a prominent transmittance peak around 532 nm, indicating the TP cavity mode. The observed TP mode is sufficiently large to induce nonlinear effects at low input intensities. This is confirmed by the open aperture z-scan results, which show a decreased transmittance at the focus characteristic of Reverse Saturable Absorption (RSA) behavior, which becomes steeper for the TP cavity structure compared to the bare Au@C core-shell reference film. The effective nonlinear absorption coefficient obtained for the TP structure is 37 times larger than the reference film containing the core-shell nanoparticles. This giant enhancement in the absorptive nonlinearity arises from the enormous energy concentrated in the spacer layer due to the presence of localized TP mode allowing stronger light-matter interaction.
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