Influence of intensity distribution of laser beam on the properties of nanoparticles obtained by laser ablation of solids in liquids

Control over the properties of nanoparticles obtained by laser ablation in liquids is experimentally demonstrated via modulation of the beam intensity profile on the target. Mask projection scheme was used with either a copper laser (wavelength of 510. 6 nm, pulse duration of 10ns) or with a Ti:sapphire laser (wavelength of 800 nm and pulse duration of 200 fs). Si and ZnSe were chosen as target materials. Obtained nanoparticles were characterized using Transmission Electron Microscopy (TEM), optical absorption spectroscopy and photoluminescence. It was shown that that size of Si nanoparticles depends on the spatial profile of the laser beam.Comment: Reported at E-MRS 2009 conference, Strasbourg, France, June 8 - 1

Initiation of nuclear reactions under laser irradiation of Au nanoparticles in the presence of Thorium aqua-ions

Initiation of nuclear reactions in Thorium nuclei is experimentally studied under laser exposure of Au nanoparticles suspended in the aqueous solution of Th(NO3)4 (232Th). It is found that the reaction pathway depends in which water, either H2O or D2O, the laser exposure is carried out. Saturation of the liquids (H2O or D2O) with gaseous H2 or D2, respectively, enhances the nuclear reactions under laser exposure allowing their excitation at peak intensity as low as 1010 W/cm2. Enhanced gamma-activity of the probe is observed after the end of laser exposure for several hours.Comment: Reported at E-MRS 2009 conference, June 8-12, Strasbourg, Franc

Hydrogen emission under laser exposure of colloidal solutions of nanoparticles

We report the generation of molecular hydrogen from water by laser irradiation, without any electrodes and photocatalysts. A near infrared pulsed nanosecond laser is used for exposure of colloidal solution of Au nanoparticles suspended in water. Laser exposure of the colloidal solution results in formation of plasma of laser breakdown of liquid and emission of H2. The rate of H2 emission depends critically on the energy of laser pulses. There is a certain threshold in laser fluence in liquid (around 50 J/cm2) below which plasma disappears and H2 emission stops. H2 emission from colloidal solution of Au nanoparticles in ethanol is higher than that from similar water colloid. It is found that formation of plasma and emission of H2 or D2 can be induced by laser exposure of pure liquids, either H2O or D2O, respectively. The results are interpreted as water molecules splitting by direct electron impact from breakdown plasma.Comment: 12 pages, 12 figure

Generation of nanoparticles of phtalocyanines by laser fragmentation and their interaction with gold nanoparticles

Optical properties and morphology of laser generated Aluminum and Copper phthalocyanine nanoparticles (nAlPc and nCuPc) in water are experimentally studied. Near infrared laser source of nanosecond pulse duration was used for fragmentation of Pc micro-powder suspended in H2O. Extinction spectra in the visible and near IR range of NPs colloidal solutions in MQ water were acquired by means of optical spectroscopy. The optical density of both nCuPc and nAlPc increases with laser fragmentation time. Transmission electron microscopy was used for characterization of nanoparticle morphology and size analysis. It is found that nCuPc are made of short (100 nm) rectangular bars interconnected at various angles with other bars. Similar experiments were carried out for a colloidal solution, which is a mixture of Au and AlPc nanoparticles. It turned out that Au NPs in presence of nAlPc form large agglomerates of Au

Self-organization of ascending bubbles ensemble

Self-organization of hydrogen bubbles generated by laser-treated areas of an aluminum plate etched in a basic aqueous solution of ammonia is studied experimentally and theoretically. A dynamics of establishment of stationary pattern of gas bubbles is experimentally is shown. In the theoretical model the velocity field of liquid flows around an ensemble of several bubbles is obtained. Modeling of the process of self-organization of gas bubbles is performed on the basis of continuum model of bubbles jet. Under certain assumptions, the pressure of diluted gas bubbles is described by equation similar to that for non-ideal gas that follows the van der Waals equation of state. The model predicts an alignment of gas bubbles along bisectors of the laser-treated area limited by a square, which is in good agreement with experimental observations. Further development of the model leads to the equation with negative diffusion coefficient that may be responsible for symmetry breakdown and pattern formation

Laser-assisted coloration of Ti: oxides or nanostructures?

Coloration of a Ti target under its ablation with picosecond laser pulses in liquids is ascribed to the formation of self-organized nanostructures. The density of nanostructures increases in an avalanche-like way with the number of laser pulses. The Raman peaks observed in the laser-exposed areas may be due to the auto-SERS effect

Laser-induced synthesis and decay of Tritium under exposure of solid targets in heavy water

The processes of laser-assisted synthesis of Tritium nuclei and their laser-induced decay in cold plasma in the vicinity of solid targets (Au, Ti, Se, etc.) immersed into heavy water are experimentally realized at peak laser intensity of 10E10-10E13 Watts per square centimeter. Initial stages of Tritium synthesis and their laser-induced beta-decay are interpreted on the basis of non-elastic interaction of plasma electrons having kinetic energy of 5-10 eV with nuclei of Deuterium and Tritium, respectively

Deviation from secular equilibrium

Laser exposure of gold nanoparticles in aqueous solutions of Uranium salt leads to accelerated decay of U238 nuclei and significant deviation from secular equilibrium. The samples demonstrate the enhanced gamma emission in the range of 54 keV during laser exposure

Contactless transfer of angular momentum by rotating laser beam

Contactless transfer of angular momentum from rotating laser beam to a solid target is experimentally demonstrated. The effect is observed under irradiation of a glassy carbon target immersed in water by a pulsed laser beam that is scanned across the target surface along circular trajectory. The direction of target rotation coincides with that of the laser beam at small thickness of the liquid layer above the target while is opposite in case of higher thickness of the layer. The effect is interpreted as the interplay between thermocapillary and convective flows induced in the liquid by laser heating

Self_organization of gas bubbles

Self_organization of hydrogen bubbles is reported under etching of metallic Aluminum in a weakly basic solution. The ascending gas bubbles drift to the areas with higher density of bubbles due to pressure difference. As a result, ascending bubbles form various stationary structures whose symmetry is determined by the symmetry of the etched area. The process is modeled on the basis of numerical solution of Bernoulli equation