Abstract
Abstract Localized surface plasmon resonance (LSPR) of metallic nanoparticles (NPs) can generate and enhance the nonlinear optical (NLO) response and has been widely used in biosensing, optical bistability, optical switch, and modulator, surface-enhanced spectroscopies, etc. Here, the two-dimensional (2D) Au & Ag hybrid plasmonic NP network (Au & Ag HPNN) were synthesized by assembling Au and Ag NPs in ethanol solvent and transferring onto a CaF2 substrate. The frequency-domain finite element method (FEM) simulations were performed to explore their LSPR properties, demonstrating the broadband optical responses throughout visible, near-infrared and mid-infrared regions. The ultrafast carrier relaxation times were determined to be 3.9, 5.6, and 8.6 ps, while the nonlinear absorption coefficients were −1.12 × 104, −1.71 × 104, and −2.54 × 104 cm/GW, respectively, for the three wavelengths matching the LSPRs peaks at 1.0, 2.0, and 3.0 μm bands. Furthermore, passively Q-switched (PQS) solid-state lasers operating at 1062.8, 1990.8, and 2947 nm were demonstrated with 2D Au & Ag HPNN based saturable absorbers. This work not only reveals desirable ultrafast broadband NLO responses of 2D HPNN, but also provides a platform for investigating their applications in nanophotonic devices.
Highlights
Nonlinear optical (NLO) response plays a significant role in modern nanophotonics, which generates a great deal of interests in the design, preparation, and characterizations of new nonlinear optical (NLO) nanomaterials
The NLO responses of metallic NPs are in a large extent determined by the plasmonic resonances (surface plasmon resonance (SPR) for extended metallic surfaces, and localized surface plasmon resonance (LSPR) for metallic NPs), which are the conduction electron coherent oscillations stimulated by the incident light and strongly dependent on NPs’ geometry and surroundings [1, 8,9,10,11,12,13]
The transmission electron microscopy (TEM) and histograms of the monodisperse particle sizes of Au NPs and Ag NPs shown in Figure S1 are made up of 16 ± 0.5 nm Au NPs and 23 ± 2 nm Ag NPs
Summary
Nonlinear optical (NLO) response plays a significant role in modern nanophotonics, which generates a great deal of interests in the design, preparation, and characterizations of new NLO nanomaterials. The NLO responses of metallic NPs are in a large extent determined by the plasmonic resonances (surface plasmon resonance (SPR) for extended metallic surfaces, and localized surface plasmon resonance (LSPR) for metallic NPs), which are the conduction electron coherent oscillations stimulated by the incident light and strongly dependent on NPs’ geometry and surroundings [1, 8,9,10,11,12,13] It provides a great platform for modulating the optical responses by tuning the metallic NPs’ shapes, sizes, and environments, etc. Novel NLO responses can be presented when mixing Au NPs and Ag NPs together to form the hybrid 1D chains or 2D network due to the coupling of the plasmonic effects like alloy or bimetallic nanostructures, which has proved to exhibit much better and larger tunability of NLO properties than that of mono-element NPs [23]. The results eomonstrated that the Au & Ag HPNN SA can support pulse modulation in the nearinfrared to mid-infrared band in solid state lasers
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