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We report the investigation of the influence of periodic metallic arrays on the emission properties of organic emitters. Beforehand, the study of the coupling process between nanoparticles through the analysis of the extinction spectra related to Rayleigh anomalies indicate the crucial role of those latter in defining the nature of the excited grating modes. The obtained results emphasis that Rayleigh Anomalies can be considered as the intermediate between individual plasmonic and collective photonic responses. Thereafter, the experimental and numerical studies of the lattice modes and their associated effects on the lifetime and emission directivity of nearby emitters indicate that tuning the geometrical grating parameters offers a possibility to select a particular coupling process from a localized effect to a far field response. Depending on the coupling strength, the emission can be strongly altered by increasing the density of states or providing diffractive orders. Eventually, this study reports that the Rayleigh Anomalies play the role of an excitation source which drives the nanoparticles to act as a set of diffractive objects for shaping the emission to be highly directive. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO) thin films were grown on glass substrates at room temperature using RF magnetron sputtering technique. Effect of the post-annealing for 1 h at 400-600 °C on the structural, morphological, optical and waveguide properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectrophotometry and m-lines spectroscopy (MLS). XRD studies show that as-grown and post-annealed TiO films exhibit (101) XRD peak corresponding to the anatase phase of TiO. Higher annealing temperatures result in a significant increase in crystallinity. The grain size values were calculated and found to be about 15-37 nm. From the analyses made on the SEM micrographs and AFM images, it was revealed that the morphology and surface roughness of the thin films were influenced by the heat treatment temperature. The UV-visible spectroscopy analyses show that as-grown TiO films were transparent in the visible region with an average transmittance of more than 75 % and the transmittance decreases slightly with an increase in annealing temperature. Annealed TiO films also exhibit an increase in the values of direct optical band gap. MLS measurements at 633-nm wavelength put into evidence that TiO planar waveguides demonstrate a well-guided fundamental mode for both transverse electric and transverse magnetic polarized light. Moreover, the refractive index was found to increase with temperature and to approach to the anatase TiO single-crystal value for the TiO film annealed at 600 °C. [ABSTRACT FROM AUTHOR]

ZnO thin films were deposited at room temperature onto glass substrate by RF sputtering technique. Effects of the post-annealing at 300-500°C on the structural, morphological, optical and waveguiding properties were investigated using different characterization techniques. X-ray diffraction (XRD) analyses have shown that all thin films have a hexagonal wurtzite structure with higher c-axis preferred orientation (002), better crystallinity and larger crystallite size as post-annealing temperature increases. Fourier transform infrared (FTIR) spectra of annealed samples confirmed that the ZnO stretching vibration bond was found to be stable at 419 cm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images have revealed that film morphology and surface roughness were influenced by heat treatment temperatures. The UV-Vis-NIR spectrophotometry characterisations have indicated that all the films were highly transparent with average transmittance exceeding 81% within the visible region, and the bandgap energy of the as-deposited film was increased with increasing of the annealing temperature.The obtained results from m-lines spectroscopy (MLS) measurements at 632.8 nm wavelength have demonstrated that all ZnO thin film optical waveguides were single mode and the ordinary and extraordinary refractive index values of the film annealed at 500°C were very close to the corresponding ZnO single-crystal values. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We report a detailed study of multiple wavelengths optical parametric generation in a single grating one-dimensional periodically poled lithium tantalate crystal. Simultaneous collinear and non-collinear generations are observed around the pump collinear direction. Similar spectra are found in continuous spatial positions symmetrical to the collinear direction, with decreasing signal and increasing idler wavelengths, associated with decreasing powers when the far-field angle increases. A phase matching scheme is proposed to describe these interactions. Numerical simulations emphasize the agreement of our phase matching scheme with the experimental results. Single-pass gain and high pump power density are very likely at the origin of the simultaneous collinear and non-collinear QPM interactions. [ABSTRACT FROM AUTHOR]