Tamm plasmon-polaritons (TPPs), formed at the interface of a plasmon-active metal and a distributed Bragg reflector (DBR), are characterized by sharp resonances in the reflection spectrum. The features of these sharp TPP resonances are primarily dictated by the structural parameters as well as by the nature of materials of the constituent DBR and metal. In the present investigation, we experimentally and theoretically analyze the role played by the DBR parameters and the metal layer thickness in determining the efficiency of TPP-mode excitation using plane waves. The findings reveal that the minimum in the reflection spectrum depicting the TPP resonance is strongly influenced by the thickness of plasmon-active metal film as well as the number of DBR unit cells. In fact, there exists an optimum combination of the geometrical parameters for achieving a maximum coupling to TPP modes. A brief theoretical analysis elucidating the underlying mechanism behind such observations is also presented so as to optimally design TPP-based architectures for different applications.
We have investigated the manifestations due to Manganese (Mn)-doping in ZnO sub-wavelength rods (or nanorods) on its nonlinear optical properties, namely two-photon absorption (TPA) and nonlinear refraction using single-beam Zscan technique. Mn-doped ZnO nanorods (NRs) were prepared by low temperature aqueous growth technique. The results show that Mn-doping concentration primarily determines whether ZnO NRs would exhibit saturable absorption (SA) or two-photon-absorption (TPA) characteristics in an openaperture experiment. At high Mn-doping concentrations, ZnO NRs exhibit SA behaviour which could be attributed to high occupation probability of defects states as well as saturation of linear absorption of subwavelength rod aggregates at high optical fluence. In contrast to high Mn-doping concentration in ZnO NRs, we observed TPA feature in 0.5% Mn-doped ZnO NRs. The employability of such structures in the area of optical limiting and switching is essentially derived from the possibility to tune the nonlinear optical absorption which could be realized by appropriate Mn-doping in ZnO NR architecture.
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