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Highlights: [•] WSe1.7/57Fe/54Fe multilayer structure was created by laser plasma ion implantation. [•] Experimental diagnostics and modeling of ion treatment were performed. [•] Modeling was carried out using a particle-in-cell method in 1D approximation. [•] Mossbauer studies indicated formation of Fe–Se, and Fe–W phases after treatment. [ABSTRACT FROM AUTHOR]

Abstract: We hereby present results on ion acceleration mechanisms in non equilibrium plasmas generated by microwaves or high intensity laser pulses. Experiments point out that in magnetized plasmas X–B conversion takes place for under resonance values of the magnetic field, i.e. an electromagnetic mode is converted into an electrostatic wave. The strong self-generated electric field, of the order of 107 V/m, causes a E × B drift which accelerates both ions and electrons, as it is evident by localized sputtering in the plasma chamber. These fields are similar (in magnitude) to the ones obtainable in laser generated plasmas at intensity of 1012 W/cm2. In this latter case, we observe that the acceleration mechanism is driven by electrons drifting much faster than plasma bulk, thus generating an extremely strong electric field ∼107 V/m. The two experiments confirm that ions acceleration at low energy is possible with table-top devices and following complementary techniques: i.e. by using microwave-driven (producing CW beams) plasmas, or non-equilibrium laser-driven plasmas (producing pulsed beams). Possible applications involve ion implantation, materials surface modifications, ion beam assisted lithography, etc. [Copyright &y& Elsevier]

Abstract: The collision of two aluminium plasmas was investigated by combining both time and space resolved spectroscopy and Langmuir probe measurements. Plasma plumes were produced by a Continuum™ Surelite Nd:YAG Laser System with pulse duration of FWHM of 6ns and wavelength of 1064nm, at a laser irradiance of 1011 W/cm2 on slab Al targets. By analyzing the emission spectra, the temporally and spatially resolved electron density and electron temperature at the stagnation layer were extracted, with a time resolution of 10ns. Data analysis confirms that the electron density of the stagnation layer evolves over a longer timescale than in the single plume case. On the other hand, the temperature trends show that the electron temperature decreases much more rapidly at the stagnation layer than in the case for the single expanding plasma. In addition, a Langmuir probe was used to investigate the properties of the collisional front evolution. The overall experimental results show that colliding laser produced plasmas could be useful in the design of experiments devoted to fusion reaction rate measurements in a low energy domain by including the effect of the electron screening (ES). [Copyright &y& Elsevier]

Abstract: We report the effects of relative time delay of plasma plumes on thin garnet crystal films fabricated by dual-beam, combinatorial pulsed laser deposition. Relative plume delay was found to affect both the lattice constant and elemental composition of mixed Gd3Ga5O12 (GGG) and Gd3Sc2Ga3O12 (GSGG) films. Further analysis of the plasmas was undertaken using a Langmuir probe, which revealed that for relative plume delays shorter than ∼200μs, the second plume travels through a partial vacuum created by the first plume, leading to higher energy ion bombardment of the growing film. The resulting in-plane stresses are consistent with the transition to a higher value of lattice constant normal to the film plane that was observed around this delay value. At delays shorter than ∼10μs, plume propagation was found to overlap, leading to scattering of lighter ions from the plume and a change in stoichiometry of the resultant films. [Copyright &y& Elsevier]

Abstract: The physical processes of pulsed laser deposition (PLD) change strongly from the initial light absorption in a target to the final deposition and growth of a film. One of the primary advantages of PLD is the stoichiometric transfer of material from target to a film on a substrate. Even for a stoichiometric flow of material from a multicomponent target, the simultaneous arrival of the target atoms is not sufficient to ensure a stoichiometric film growth. The laser fluence has to be sufficiently high to induce ablation rather than pure evaporation from target, but a high fluence may lead to preferential (self)sputtering and possibly implantation of the light atoms in the film. A background gas of a sufficiently high pressure may reduce sputtering of the film, but may lead the preferential diffusion of the light component to the substrate. The importance of these processes during the entire PLD process will be discussed. [Copyright &y& Elsevier]

Abstract: Titanium was laser nitrided by means of free-electron laser irradiation in pure nitrogen atmosphere. The variation of pulse frequency and macropulse duration of the free electron laser resulted in δ-TiN x coatings with different thickness and different micro- and macroscopic morphologies. The coatings revealed, characteristic values for hardness, roughness and crystallographic texture, which originate from the growth mechanism, the solid–liquid interface energy and the strain. Further investigations showed that the dendritic growth is beginning at the surface and that the alignment of dendrites is normal to the surface. A correlation of the texture with the time structure of the laser pulses was found. Numerical simulations were performed and compared with the experimental results. The simulations can explain the experimental results. [Copyright &y& Elsevier]

Abstract: The production of nanoparticles via femtosecond laser ablation of gold and copper is investigated experimentally involving measurements of the ablated mass, plasma diagnostics, and analysis of the nanoparticle size distribution. The targets were irradiated under vacuum with a spot of uniform energy distribution. Only a few laser pulses were applied to each irradiation site to make sure that the plume expansion dynamics were not altered by the depth of the laser-produced crater. Under these conditions, the size distribution of nanoparticles does not exhibit a maximum and the particle abundance monotonously decreases with size. Furthermore, the results indicate that two populations of nanoparticles exist within the plume: small clusters that are more abundant in the fast frontal plume component and larger particles that are located mostly at the back. It is shown that the ablation efficiency is strongly related to the presence of nanoparticles in the plume. [Copyright &y& Elsevier]

Abstract: Carbides and nitrides play an important role for technological applications. Here, we present a new promising technique for a direct laser synthesis of carbides and nitrides by pulsed laser irradiation in reactive atmospheres, e.g. methane and nitrogen. A number of laser types have been used (excimer laser, Nd:YAG, Ti:sapphire, free electron laser) and a number of different nitrides and carbides have been produced (e.g. TiN, AlN, Fe3C, SiC). The mechanisms and examples will be presented and it will be shown that also the lateral and in depth structuring can be modified from nanoscale to mesoscale. The dependence of phase formation and resulting properties are given in relation to the laser treatment parameters, such as laser type, pulse duration, material and reactive gas pressure. This reactive laser synthesis can also be used for the improvement of steel surfaces. For example, the irradiation of pure iron in methane atmosphere at low pressures or low number of laser pulses results in the formation of an amorphous carbon surface layer and hexagonal -Fe1−xCx, which is more and more transformed into cementite when increasing the number of pulses or the gas pressure. [Copyright &y& Elsevier]

Abstract: Recently, we proposed a new PLD geometry, termed as inverse PLD, in which the backward motion of the ablated species was utilized for film growth on substrates lying in the target plane. Qualitative measurements revealed that in this geometry the growth rate of carbon nitride films was comparable to or even exceeded that of the traditional geometry in the critical pressure domain of reactive PLD. The knowledge of the lateral distribution of the growth rate is of primary importance for both applications and modelling. Here first quantitative data on the dependence of the lateral distribution of deposition rate of carbon nitride films, fabricated by KrF excimer laser ablation of a rotating graphite target, on N2 pressure are reported. Thickness distributions of films grown on Si substrates within the 0.5–50Pa pressure window have been recorded along the axes of symmetry of the laser spot by stylus profilometry. At all background pressures, the thickness decreases exponentially with increasing distance from the ablating laser spot. The elliptical symmetry typical at low pressures and near to the spot shifts to circular with increasing pressure and distance. The existence of flip-over suggests that recondensation of the plasma species without scattering on the surrounding atmosphere effectively contributes to IPLD film growth. [Copyright &y& Elsevier]

To study the solid Cu ablation in vacuum, two different laser sources operating at 1064 and 308 nm wavelength are employed at similar values of laser fluences. The infrared laser is a Q-switched Nd:Yag having 9 ns pulse width (INFN-LNS, Catania), while the ultraviolet one is a XeCl excimer having 20 ns pulse width (INFN-LEA, Lecce). Both experiments produced a narrow angular distribution of the ejected material along the normal to the target surface. The ablation showed a threshold laser power density, of about 7 and 3 J/cm2 at 1064 and 308 nm, respectively, below which the ablation effect was negligible. The laser interaction produces a plasma at the target surface, which expands very fast in the vacuum chamber. Time-of-flight (TOF) measurements of the ion emission indicated an average ion velocity of the order of 4.7×104 and 2.3×104 m/s for the infrared and ultraviolet radiation, respectively. We also estimated approximately the corresponding temperature of the plasma from which ions originated, i.e. about 106 and 105 K for IR and UV wavelength, respectively. A discussion of the analysis of the ablation mechanism is presented. At the used laser power densities the produced Cu ions showed ionisation states between 1+ and 5+ in both cases. [Copyright &y& Elsevier]

Time and space resolved optical emission spectroscopy has been used to investigate the characteristics of the plasma plume generated during the KrF laser ablation of Cr2O3 targets in vacuum. The nature of plasma species, their energies, their space and temporal distributions were established. We showed that the species with high excitation energies (O(II) ions, E ∼25–30 eV) dominate the emission at intermediate plasma stages of evolution and near the target, followed by Cr(II) (E ∼3–16 eV), O(I) (E 10–16 eV) and Cr(I) (E ∼3–6 eV), which appear during plasma cooling. Peculiarly, the O(I) species gives lines in the 600–800 nm spectral range. Optical time-of-flight (TOF) measurements showed velocities around 3.6×104 m/s for the ionic species and 1.3×104 m/s for the neutral species. [Copyright &y& Elsevier]

We have developed a new pulsed laser deposition (PLD) method named “Aurora PLD” under application of the magnetic field from the substrate side. It is characterized by an activation and/or enhanced ionization of the ablated particles during transport from the target to substrate. Many basical findings suggested that the main mechanism is the electron recoil arising from the magnetic mirror effect which, in turn, gives rise to interaction of energetic electrons and atoms (or ions). It resulted in the room temperature epitaxy of (1 0 0)NiO on (0 0 1)MgO. Using the water-cooled magnetic platelet located between the target and substrate, the Eclipse–Aurora PLD worked well even at the heated substrate. Much better quality in SrTiO3 film was obtained by this improved PLD. [Copyright &y& Elsevier]

Intensity, temperature and electron density distributions of laser-induced plasmas (LIPs) have been measured by emission spectroscopy with two-dimensional spatial resolution and temporal resolution. The plasmas have been generated with an iron sample at different pressures of air, in the range 10–1000 mbar. An experimental system based in an imaging spectrometer equipped with an intensified CCD detector has been used to obtain the spectra with two-dimensional spatial resolution. The evolution of the intensity distributions is described by the blast wave model only at initial times. The temperature distributions are shown to correspond to a slight difference between the intensity distributions of two Fe I emission lines that have a high difference of their upper energy levels (3.38 eV). The electron density distributions have similar features to those of the temperature distributions. The features of the intensity and temperature distributions show a significant change with the ambient gas pressure: they have separated maxima in the plasmas generated at pressures below 100 mbar, whereas at higher pressures, the maxima of the two distributions coincide. [Copyright &y& Elsevier]

The application of laser-induced breakdown spectroscopy (LIBS) to determine the composition of thin films produced by pulsed laser deposition (PLD) has been investigated. The targets were Fe–Ni alloys with Fe concentrations in the range 0.2–80 wt.% and the ablated material was deposited onto glass substrates. The same infrared Nd:YAG laser was used for the film deposition, carried out in vacuum, and for the analysis, performed in air at atmospheric pressure. The single-shot line intensities emitted by the laser plasma generated with the films are up to 16 times higher than those emitted by the plasma obtained with an equivalent bulk sample. A similar plasma temperature of about 7000 K has been measured with both types of samples. Those results indicate that the ablation process is much more efficient for the films than for the bulk samples. Calibration curves of the element contents in the films have been obtained, showing good correlation and low standard deviations, typically 5% RSD. The detection limit for Fe is 300 ppm. From the LIBS data, the stoichiometry and homogeneity of the film composition has been deduced. [Copyright &y& Elsevier]

The property of soft X-ray generation from Xe clusters irradiated with intense lasers was studied. The wavelength, the pulse width, and the pump energy were widely varied. Through this survey, even with the comparatively low-density Xe jet of <5×1018 cm−3 average atomic density, the highest conversion efficiency of over 10% from laser energy to soft X-ray (5–18 nm) was obtained with a femtosecond KrF laser pulse, where a 4π source was assumed. [Copyright &y& Elsevier]

The complex of experimental installations for studying of laser radiation interaction with surface of metal and dielectrics is established at High Current Electronics Institute (HCEI, Tomsk, Russia). The complex consist of laser systems (λ—from IR to UV region, pulse duration from ns to ms, energy up to 2 kJ, average power up to 1 kW), experimental cell for disposition of samples (gas pressure from 10−5 Torr to 10 atm) and also spectroscopic and measurement equipment. A number of experimental results on the study of laser plasma formation and expansion in vacuum and dense gas, laser breakdown in high pressure SF6, UV lasers irradiation of diamond and IR and UV lasers interaction with steel surface are presented. [Copyright &y& Elsevier]