Influence of the dielectric substrate on the effective optical constants of silver plasmonic films.

The effective optical properties of plasmonic thin films can be used to model the far-field response of nanostructured materials to an incident electromagnetic field. In the present work, optically thin nanostructured silver (Ag) plasmonic films were fabricated on transparent dielectric substrates of soda-lime glass, sapphire, and fused silica using oblique angle deposition. The influence of the underlying dielectric substrate on the effective optical properties of the nanostructured layer was investigated by an ellipsometric-optical model based on Mueller matrix ellipsometry. The wavelength-dependent uniaxial optical responses of the nanostructured Ag films fabricated on sapphire were modeled with three Gaussian and one Tanguy oscillator, representing key optical phenomena over the range from 300 to 1000 nm. In comparison with the same Ag films on glass, the results confirm that the effective optical properties cannot be considered in isolation from the substrate. As expected, the extinction peak associated with the localized surface plasmon resonance was redshifted by approximately 220 nm per unit of the substrate refractive index. Importantly, it was found that the direction of incidence also influences the film behavior, with a substantial redshift in the extinction peak for light directed through the dielectric compared to free-space illumination. This property can have a significant effect on the far-field performance of these films.

Effective optical constants of anisotropic silver nanoparticle films with plasmonic properties: erratum.

This erratum reports a correction to Fig. 5 in the original manuscript, Opt. Lett.41, 5495 (2016)OPLEDP0146-959210.1364/OL.41.005495.

Effective optical constants of anisotropic silver nanoparticle films with plasmonic properties.

Mueller matrix ellipsometry has been used to determine the effective optical constants of island-like Ag films deposited by thermal evaporation. These films depart substantially from bulk silver with a prominent localized surface plasmon resonance. Moreover, despite the isotropic appearance, they exhibit uniaxial optical properties with the optical axis inclined by 83.4° from the substrate normal toward the direction of the incoming vapor flux. The uniaxial model supports the plasmon resonance peaks revealed by in-plane absorbance measurements of the films. The uniaxial behavior suggests that the resonances along the ordinary axes are weakly coupled between neighboring particles, whereas the extraordinary resonance is relatively strongly coupled. Therefore, the anisotropy should be considered in the practical applications of these plasmonic films.

Characterization of time-resolved fluorescence response measurements for distributed optical-fiber sensing.

A distributed optical-fiber sensing system based on pulsed excitation and time-gated photon counting has been used to locate a fluorescent region along the fiber. The complex Alq3 and the infrared dye IR-125 were examined with 405 and 780 nm excitation, respectively. A model to characterize the response of the distributed fluorescence sensor to a Gaussian input pulse was developed and tested. Analysis of the Alq3 fluorescent response confirmed the validity of the model and enabled the fluorescence lifetime to be determined. The intrinsic lifetime obtained (18.2±0.9 ns) is in good agreement with published data. The decay rate was found to be proportional to concentration, which is indicative of collisional deactivation. The model allows the spatial resolution of a distributed sensing system to be improved for fluorophores with lifetimes that are longer than the resolution of the sensing system.

Visible and near infra-red up-conversion in Tm3+/Yb3+ co-doped silica fibers under 980 nm excitation.

The spectroscopic properties of Tm(3+)/Yb(3+) co-doped silica fibers under excitation at 980 nm are reported. Three distinct up-conversion fluorescence bands were observed in the visible to near infra-red regions. The blue and red fluorescence bands at 475 and 650 nm, respectively, were found to originate from the (1)G(4) level of Tm(3+). A three step up-conversion process was established as the populating mechanism for these fluorescence bands. The fluorescence band at 800 nm was found to originate from two possible transitions in Tm(3+); one being the transition from the (3)H(4) to (3)H(6) manifold which was found to dominate at low pump powers; the other being the transition from the (1)G(4) to (3)H(6) level which dominates at higher pump powers. The fluorescence lifetime of the (3)H(4) and (3)F(4) levels of Tm(3+) and (2)F(5/2) level of Yb(3+) were studied as a function of Yb(3+) concentration, with no significant energy back transfer from Tm(3+) to Yb(3+) observed.

Absorption of thin film materials at 10.6 microm.

Absorption indices at a wavelength of 10.6 mum for thin films of As(2)S(3), GeSe, BaF(2), ZnSe, and CdTe were measured by calorimetric techniques with a CO(2) laser. The values obtained, 4.6 x 10(-4), 1.4 x 10(-3), 2.8 x 10(-3), 2.8 x 10(-3), and 5.0 x 10(-3), respectively, were significantly greater than the corresponding values for the bulk materials. This difference was least for the vitreous films, As(2)S(3) and GeSe, which also had a lower absorption than the remaining polycrystalline films. Details are presented of the microstructure of the films as determined by scanning electron microscopy and k-ray diffraction.

Time-resolved beam structure of an active Q-switched ruby laser.

Time-resolved observations show that the near field and far field patterns of an active Q-switched ruby laser remain almost constant for the duration of the output pulse. This is in marked contrast to the reported behavior of a passive Q-switched laser.