We demonstrate highly efficient avalanche multiphoton luminescence (MPL) from ordered-arrayed gold nanowires (NWs) with low time-average excitation intensity, Iexc (5.0-9.1 kW/cm2). The intensity of avalanche MPL, IMPL, is about 10(4) times larger than that of three-photon luminescence, the slope partial differential log IMPL/ partial differential log Iexc of avalanche MPL reaches as high as 18.3, and the corresponding polarization dependence of IMPL has a form of cos50 phip. The emission dynamics of avalanche MPL and three-photon luminescence are also studied comparatively. These observations indicate that the highly efficient avalanche MPL is attributed to the giant enhancement and coupling of longitudinal surface plasmon resonance of ordered-arrayed gold NWs.
Porous anodic aluminum oxide (AAO) Bragg stacks were fabricated by a modified two-step anodization, and the optical transmittance spectra of AAO Bragg stacks soaking in varied analytes (air, series of alcohols and alkanes) were collected. The results show that both the wavelength and the intensity of the reflected light are sensitive to the analyte’s refractive index and infiltration; e.g., for any two adjacent analytes in a series of alcohols or alkanes, the difference of transmittance in dip is greater than 3%. This phenomenon enables us to fabricate chemical and biological sensors and in situ monitor the organic chemical reaction just by analyzing the intensity of the reflected light without a spectrophotometer.
We report the fabrication of micro/nanoscale pits with facile shape, orientation, and size controls on an Si surface via an Au-nanoparticles-assisted vapor transport method. The pit dimensions can be continuously tuned from 70 nm to several mum, and the shapes of triangles, squares, and wire/hexagons are prepared on Si (111), (100), and (110) substrates, respectively. This reliable shape control hinges on the anisotropic diffusivity of Co in Si and the sublimation of cobalt silicide nanoislands. The experimental conditions, in particular the substrate orientation and the growth temperature, dictate the pit morphology. On the basis of this understanding of the mechanism and the morphological evolution of the pits, we manage to estimate the diffusion coefficients of Co in bulk Si along the 100 and 111 directions, that is D(100) and D(111). These diffusion coefficients show strong temperature dependence, for example, D(100) is ca. 3 times larger than D(111) at 860 degrees C, while they approach almost the same value at 1000 degrees C. This simple bottom-up route may help to develop new technologies for Si-based nanofabrication and to find potential applications in constructing nanodevices.
An in-line, highly sensitive refractive index (RI) sensor based on a tapered multicore fiber (MCF) structure sandwiched between two single-mode fibers is proposed and demonstrated. The fiber tapering technique was employed to fabricate in-line interferometers based on the multicore fiber. The waist diameter is one of the dominant factors of the intercore coupling. The tapered MCF interferometer is highly sensitive to the surrounding refractive index with a maximum sensitivity of 9194.6 nm/RIU in the RI range of 1.4264 to 1.4278 when the waist diameter is 9 µm. The enhancement of the evanescent field by graphene coating is proved to be able to improve the RI sensitivity further. A graphene-coated MCF interferometer with waist diameter of 9 µm offers the maximum sensitivity of 12617.6 nm/RIU in the RI range of 1.4144 to 1.4159. The experimental data have good agreement with the simulated results.
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