M. Bahoura

Threshold and slope efficiency of Nd0.5La0.5Al3(BO3)4 ceramic random laser: effect of the pumped spot size

Abstract We have experimentally found that in a random laser based on Nd 0.5 La 0.5 Al 3 (BO 3 ) 4 scattering ceramic, the threshold pumping density decreases and the output slope efficiency increases with the increase of the diameter of the pumped spot. The experimental behavior is explained in terms of random photons walk in an amplifying medium.

Extreme tunability in aluminum doped Zinc Oxide plasmonic materials for near-infrared applications

Plasmonic materials (PMs), featuring large static or dynamic tunability, have significant impact on the optical properties due to their potential for applications in transformation optics, telecommunications, energy, and biomedical areas. Among PMs, the carrier concentration and mobility are two tunable parameters, which control the plasma frequency of a metal. Here, we report on large static and dynamic tunability in wavelengths up to 640 nm in Al-doped ZnO based transparent conducting degenerate semiconductors by controlling both thickness and applied voltages. This extreme tunability is ascribed to an increase in carrier concentration with increasing thickness as well as voltage-induced thermal effects that eventually diminish the carrier concentration and mobility due to complex chemical transformations in the multilayer growth process. These observations could pave the way for optical manipulation of this class of materials for potential transformative applications.

Dependence of the random laser behavior on the concentrations of dye and scatterers

We have studied stimulated emission in a random laser based on rhodamine 6G dye and TiO2 nanoparticles. At both small and large concentrations of nanoparticles, the minimum threshold was found at ultra-high concentrations of dye, 20?g?L?1. With the increase in concentration of TiO2 nanoparticles, the threshold reaches its maximum at the transition from a weak-scattering regime to a strong-scattering regime, when the transport mean free path lt is approximately equal to the absorption length la. At the same value of lt, the random laser emission qualitatively changes its behavior. The experimental results are in good agreement with the predictions of a heuristic model.

Energy harvesting in semiconductor-insulator-semiconductor junctions through excitation of surface plasmon polaritons

We have demonstrated a simple approach for developing a photovoltaic device consisting of semiconductor-insulator-semiconductor (SIS) heterojunction using surface plasmon polaritons (SPPs) generated in one of the semiconductors (Al:ZnO) and propagated through the dielectric barrier (SiO2) to other (Si). This robust architecture based on surface plasmon excitation within an SIS device that produces power based on spatial confinement of electron excitation through plasmon absorption in Al:ZnO in a broad spectrum of visible to infrared wavelengths enhancing the photovoltaic activities. This finding suggests a range of applications for photovoltaics, sensing, waveguides, and others using SPPs enhancement on semiconductors without using noble metals.

Determination of the transport mean free path in a solid-state random laser

Using the coherent backscattering technique, we have measured the transport mean-free-path lengths lt for photons in NdAl3(BO3)4 powder, a promising solid-state random laser material. The developed model allows one to calculate lt as a function of the mean particle size s in tightly packed powder or sintered ceramic. The experimentally determined value of lt is in good agreement with the model prediction.

Dependence of the neodymium random laser threshold on the diameter of the pumped spot

We experimentally studied the dependence of the threshold energy density E/sub th//S in Nd/sub 0.5/La/sub 0.5/Al/sub 3/(BO/sub 3/)/sub 4/ random laser on the diameter of the pumped spot d and found that at d/spl ges/130/spl mu/m, E/sub th//S is proportional to 1/d+const. This functional dependence is different from the one commonly expected in the case of diffusion, /spl prop/1/d/sup 2/+const. However, the obtained experimental dependence does not mean the failure of the diffusion model. Calculating the mean photons residence time /spl tau//sub res//sup p/ (which photons, making their diffusion-like random walks, spend inside the gain volume) as the function of d and further assuming that E/sub th//S/spl prop/(/spl tau//sup p//sub res/)/sup -1/, we predicted the experimentally obtained functional dependence, /spl prop/1/d+const. The major difference between our model and that of and was in the boundary conditions.

Electrical conductivity and photoresistance of atomic layer deposited Al-doped ZnO films

Al-doped ZnO films were deposited by the atomic layer deposition (ALD) on both glass and sapphire (0001) substrates. The Al composition of the films was varied by controlling the Zn:Al pulse cycle ratios. The films were characterized by the atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and optical measurements. The Film resistivity was measured as a function of Zn:Al cycle ratios as well as temperature for films grown at various substrate temperature used for ALD deposition. The resistivity of the ALD grown films decreases significantly, and so as the increase in the carrier concentration as the cycle ratio increases. The systematic measurements of temperature dependence of resistivity of films at various cycle ratios clearly demonstrate the crossover of the metal–semiconductor–insulator phase with the function of temperature as well as the cycle ratios. The average transmission of all films is greater than 85% and the optical absorption increases significantly in the visib...

Elongation of surface plasmon polariton propagation length without gain

We have demonstrated that an addition of highly concentrated rhodamine 6G chloride dye to the PMMA film adjacent to a silver film can cause 30% elongation of the propagation length of surface Plasmon polaritons (SPPs). The possibility to elongate the SPP propagation length without optical gain opens a new technological dimension to low-loss nanoplasmonic and metamaterials.

Europium doped Gd2O3 and FeCo nanoparticles for biomedical application

Nanometer-sized particles have novel optical, electronic, magnetic or structural properties and are currently under intense development for application in cancer, cardiovascular diseases, and degenerative neurological disorders such as alzheimers disease. Targeted nanoparticle drugs offer significant advantages in improving cancer therapeutic efficacy and simultaneously reducing drug toxicity. We report here the synthesis, characterization and toxicity test of FeCo and Eu: Gd2O3 nanoparticles. Chemical routes, such ad coprecipitation and sol-gel techniques were used for the synthesis of the nanoparticles, and the surface of the nanoparticles was coated with silica. Structural and microstructural studies reveal that both type of nanoparticles 20 nm in size with very narrow size distribution. These nanoparticles demonstrate strong magnetic and optical properties at room temperature. Toxicity test shows that FeCo nanoparticles are very toxic, however toxicity decreases when the nanoparticles were coated with a thin layer of silica. However toxicity decreases when the nanoparticles were coated with a thin layer of silica. However, both uncoated and coated Eu:Gd2O3 nanoparticles show significantly reduced toxicity. Our results suggest that these nanoparticles are useful for biomedical applications. The detail of the results will be presented.

Nanopatterning of atomic layer deposited Al:ZnO films using electron beam lithography for waveguide applications in the NIR region

We have demonstrated the nanopatterning of atomic layer deposited (ALD) Al:ZnO (AZO) films using electron beam lithography (EBL) for plasmonic waveguide applications. The influence of grains on repeatable planar nanostructures by nanolithography process was studied for annealed films in order to avoid effects of granularity. Our results demonstrate that the nanopatterning of AZO by the EBL technique is limited due to granularity of ALD grown AZO films. This finding suggests the limitations of ALD grown samples for optical applications where nanopatterns are fabricated by the EBL technique. Furthermore, the ALD grown films lose conductivity orders of magnitude on annealing.