91 research outputs found
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
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
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
Stable products of laser-induced breakdown of aqueous colloidal solutions of nanoparticles
The formation of stable products of water decomposition under laser exposure
of aqueous colloidal solutions of nanoparticles is experimentally studied.
Laser exposure of colloidal solutions leads to formation of H2, O2, and H2O2.
The dependence of the yield of these products depends on the energy density of
laser radiation inside the liquid and concentration of nanoparticles. The ratio
H2/O2 depends on laser fluence and is shifted towards H2. There are at least to
sources of H2O2, namely, laser-induced breakdown plasma and ultrasound induced
by laser pulses in the liquid. The formation of both H2 and O2 is tentatively
assigned to direct dissociation of H2O molecules by electron impact from
laser-induced plasma.Comment: The paper was presented at 18th International Symposium on Laser
Precision Microfabrication, June 3-8, Toyama, Japa
Accelerated alpha-decay of 232U isotope achieved by exposure of its aqueous solution with gold nanoparticles to laser radiation
Experimental results are presented on laser-induced accelerated alpha-decay
of Uranium-232 nuclei under laser exposure of Au nanoparticles in aqueous
solutions of its salt. It is demonstrated that the decrease of alpha-activity
strongly depends on the peak intensity of the laser radiation in the liquid and
is highest at several terawatt per square centimeter. The decrease of
alpha-activity of the exposed solutions is accompanied by the deviation of
gamma-activities of daughter nuclides of Uranium-232 from their equilibrium
values. Possible mechanisms of the laser influence on the alpha-activity are
discussed on the basis of the amplification of the electric field of laser wave
on metallic nanoparticles.Comment: 9 pages, 5 figure
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
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