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.
Silver nanoparticles were prepared by pulsed laser ablation technique using a second harmonic wavelength (532 nm) of Q switched Nd:YAG laser of 7 ns pulse width and 10 Hz repetition rates. Formation of Ag NPs was confirmed from characteristic surface Plasmon resonance induced absorption (~418 nm). Spherical shape morphology and crystalline nature of structure were revealed from SEM and TEM analysis. Nonlinear optical studies were conducted by z scan analysis with the same laser system used for ablation. A switching of nonlinear absorption (saturable absorption to reverse saturable absorption) in Ag NPs were observed when on axis input intensity increased from 0.27 GW/cm2 to 0.83 GW/cm2 and it could be attributed to interplay of different nonlinear absorption mechanisms, that is strongly depends on the intensity of the excitation source. Self-defocusing nature of the sample was revealed from the closed aperture z scan analysis.
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