Search results for "absorption."
showing 10 items of 2682 documents
Improvement of photocatalytic and photoelectrochemical activity of ZnO/TiO2 core/shell system through additional calcination: Insight into the mechan…
2017
Abstract ZnO/TiO2 composites were prepared by sol-gel deposition of TiO2 on ZnO nanorods hydrothermally grown on electrically conductive indium tin oxide substrate (ITO). It has been shown that the ZnO/TiO2 interface plays a key role in enhancement of photodecomposition of methylene blue (MB) used as a model test pollutant, under monochromatic light irradiation (400 nm). The increase of photocatalytic activity was attributed to the shift of absorption edge of ZnO/TiO2 towards visible light in comparison with bare TiO2. Further enhancement of photocatalytic activity of ZnO/TiO2 was achieved through its additional calcination at 450 °C for 3 h. This treatment brings 40% increase in the rate o…
Laser plasma plume structure and dynamics in the ambient air: The early stage of expansion
2011
Laser ablation plasma plume expanding into the ambient atmosphere may be an efficient way to produce nanoparticles. From that reason it would be interesting to study the properties of these laser induced plasmas formed under conditions that are known to be favorable for nanoparticles production. In general, plume behavior can be described as a two-stage process: a “violent” plume expansion due to the absorption of the laser beam energy (during the laser pulse) followed by a fast adiabatic expansion in the ambient gas (after the end of the laser pulse). Plasma plume may last a few microseconds and may have densities 10−6 times lower than the solid densities at temperatures close to the ambie…
1.65-μm Er:Yb:YAG diode-pumped laser delivering 80-mJ pulse energy
2005
We demonstrate efficient lasing of bulk diode-pumped Er 31 :Yb 31 :YAG at 1.645 mm. The material is transversely pumped using three quasi-cw 960-nm laser diode arrays in a simple arrangement. In the free-running mode of operation, an output pulse energy of 79 mJ is obtained at 4.7 J of incident optical pump energy. The lasing threshold lies in the range 1.0 to 1.9 J in long-pulse operation, depending on pumping conditions, and optical slope efficiencies of 2.2% to 3.4% were measured with respect to the incident pump energy. Furthermore, initial Q-switching experiments with a Co:MALO saturable absorber yielded pulses of 1.7-mJ energy and 340-ns FWHM duration. As the reported laser setup also…
Heat transfer in semi-transparent materials during laser interaction
2004
Abstract A model of energy exchange, based on the finite element method is specially developed to determine the thermal field for semi-transparent polymers irradiated by laser. Our model, which uses the finite element method, allows to define the laser and specific structure characteristics in terms of density of power, speed and shape of the spotlight, material coefficient absorption, etc. The model has been experimentally validated by measuring the thermal response induced by the laser source. The experimental part of the study has been performed using a semiconductor laser diode source and an infrared thermography camera.
Near-Infrared Spectra of Water Confined in Silica Hydrogels in the Temperature Interval 365−5 K
2002
We have used a sol−gel technique to obtain optically transparent hydrogels in which water is trapped within a tridimensional disordered silica matrix. A suitable aging of these hydrogels enables to have transparent noncracking samples down to cryogenic temperatures. We report the optical absorption spectra, in the near-infrared region, of water trapped in our silica hydrogels, measured in the temperature range 365−5 K, and we compare them with the same spectra of liquid water, measured in the temperature range 365−263 K. The data show that it is possible to have noncrystallizing water even at 5 K: indeed, the overtone bands at ∼1.41 μm and at ∼1.155 μmtypical of “weakly bonded” water molec…
Quadratic nonlinear optical parameters of 7% MgO-doped LiNbO3 crystal
2016
International audience; Pure and 7% MgO-doped lithium niobate (LiNbO3) single crystals were grown by the Czochralski technique. The shift of optical absorption edge in 7% MgO-doped crystal in direction of shorter wavelength compared to undoped crystal was observed. The second harmonic generation measurements of 7% MgO-doped LiNbO3 crystal were performed at room temperature by means of the rotational Maker fringe technique using Nd:YAG laser generating at 1064 nm in picoseconds regime. Experimentally obtained value of nonlinear optical coefficient d33 for 7% MgO-doped LiNbO3 was found to be less than for undoped crystal but higher than for 5% MgO-doped. I-type phase-matched second harmonic g…
On the Possibility of Miniature Diamond-Based Magnetometers Using Waveguide Geometries
2018
Micromachines 9(6), 276 (2018). doi:10.3390/mi9060276
Production and Characterization of Oxyhydroxyapatites
2018
The amount and alignment of hydroxyl ions influence the bioactivity of hydroxyapatite. Hydroxyl ions in hydroxyapatite are the most mobile and upon heating are the first to leave the lattice to form oxyhydroxyapatite. This work describes a method for producing hydroxyapatite with different amounts of hydroxyl ions, and reports on the changes in Fourier transform infrared absorption at increasing level of dehydroxylation. Detailed analysis of spectra in the 500 – 700 cm-1 range showed a peak shift for the hydroxyl ion absorption line at 632 cm-1 to 637 cm-1 and an increase in the wavenumber for the phosphate line at 575 cm-1.
Quantum chemical simulations of the optical properties and diffusion of electron centres in mgo crystals
1996
Semiempirical quantum chemical simulations have been undertaken to obtain the self-consistent atomic and electronic structure of the two basic electron defects in MgO crystals: F+ and F centres (one and two electrons trapped by an 0 vacancy, V,). The calculated absorption and luminescence energies agree well with the experimental data; the excited states of both defects are found to be essentially delocalised over nearest-neighbour cations. The activation energy for diffusion is found to increase monotonically in a series V, --f F+ --f F centre (2.50 eV, 2.72 eV and 3.13 eV, respectively).