Formation of embedded nanoparticles in an excimer laser treated Mg alloy surface

Holmium ((lambda) equals 2.09 micrometers ) and excimer ((lambda) equals 308 nm) lasers are used for ablation of tissue. In a previous study it was demonstrated that both excimer and holmium laser pulses produce fast expanding and collapsing vapor bubbles. To investigate whether the excimer induced bubble is caused by vaporization of water, the threshold fluence for bubble formation at a bare fiber tip in water was compared between the excimer laser (pulse length 115 ns) and the Q-switched and free-running holmium lasers (pulse length 1 microsecond(s) to 250 microsecond(s) , respectively). To induce bubble formation by excimer laser light in water, the absorber oxybuprocaine-hydrochloride (OBP-HCl) was added to the water. Fast flash photography was used to measure the threshold fluence as a function of the water temperature (6 - 90 degree(s)C) at environmental pressure. The ultraviolet excimer laser light is strongly absorbed by blood. Therefore, to document the implications of bubble formation at fluences above the tissue ablation threshold, excimer laser pulses were delivered in vitro in hemoglobin solution and in vivo in the femoral artery of the rabbit. We conclude that the principal content of the fast bubble induced by a 308 nm excimer laser pulse is water vapor. Therefore, delivery of excimer laser pulses in a water or blood environment will cause fast expanding water vapor bubbles, which may induce mechanical damage to adjacent tissue.

The effects of a pulsed XeCl excimer laser (308 nm) on ultra-high-strength polyethylene (UHSPE) fibers and the fiber/epoxy resin interface were studied. SpectraTM 1000 (UHSPE) fibers were treated in air with a pulsed excimer laser with different energy density levels and numbers of pulses. Chemical and topographical changes of the fiber surfaces were characterized using X-ray photoelectron spectroscopy (XPS), dynamic wettability measurements, and scanning electron microscopy (SEM). The fiber/epoxy resin interfacial shear strength was evaluated by the single-fiber pull-out test. The XPS spectra demonstrated that the fiber surface undergoes photodissociation because of the laser treatment, which results in the incorporation of oxygen at the surface. The wettability data showed that the fiber becomes more polar after laser treatment and also more wettable. SEM photomicrographs revealed that the surface roughness of the fibers increases after the laser treatment. The interfacial shear strength (IFSS) results indicated that the laser treatment significantly improves the adhesion strength of UHSPE fibers with epoxy resin. This enhancement in IFSS is attributed to the increased roughness of the fiber surface and increased interfacial area, increased polar nature and wettability, as well as the improvement of the acid-base component of the surface energy after laser treatment.

CLINICAL APPLICATION OF UV EXCIMER LASERS

Materials processing by laser irradiation is an expanding field with attractive technological applications. Among all laser-based treatments, the irradiation of metals and semiconductors in controlled reactive atmospheres can successfully lead to important modifications on the surface of the irradiated targets. When the reactive gas contains nitrogen or carbon, the process is called laser nitriding and laser carburising, respectively. In the present work, iron, aluminium and silicon substrates have been treated in controlled nitrogen (N2) and methane (CH4) atmospheres with a pulsed XeCl excimer laser (wavelength=308 nm, pulse duration=55 ns FWHM) in order to incorporate nitrogen and carbon into the substrates. The modifications induced by the laser are analysed as a function of the various experimental parameters (gas pressure, laser fluence, number of laser pulses) and the mass transport mechanisms during the laser treatment are studied in detail. Solid solutions (Fe(N), Fe(C)) as well as stoichiometric phases (AlN, SiC) can be synthesized on the surface, forming coatings with enhanced adhesion to the underlying substrates. The experimental analysis is carried out by a number of techniques (Rutherford Backscattering Spectrometry, Resonant Nuclear Reaction Analysis, Mössbauer Spectroscopy, X-ray Absorption Fine Structure, X-ray Diffraction, Nanoindentation Hardness) in order to achieve information on the elemental distribution, the phase formation, the local atomic environment and the mechanical properties of the treated targets. By investigating the modification of the materials after the laser treatment we can also obtain a valuable insight into the mass incorporation mechanisms and the plume-surface interaction during the laser irradiation.

Effects of different laser and plasma treatments on the interface and adherence between evaporated aluminium and polyethylene terephthalate films: X-ray photoemission, and adhesion studies

The effects of excimer laser treatment on the changes in the surface topography, the physical and chemical properties of ultra-high strength polyethylene (UHSPE) fibers, and their interfacial property with epoxy resin were investigated. The scanning electron microscopy (SEM) photomicrographs show that UHSPE fibers exhibit a rougher surface after irradiation with the XeCl pulsed excimer laser as a result of intense laser heat and ablation. The wettability and surface chemistry of control and laser-treated UHSPE fibers were monitored by TRI wettability/friction apparatus. The chemical changes on the surfaces of UHSPE fibers were analyzed by Fourier transform infrared spectroscopy (FTIR) in attenuated total reflectance (ATR) mode. The tensile properties of single fibers, before and after laser treatment, were studied using an Instron tensile tester. Interfacial shear strength (IFSS) measurements were performed using the single-fiber pull-out test. The fiber surface becomes polar after the laser treatment with increased acid-base contribution. The strength of laser-treated UHSPE fibers is lower than that of the control fibers. The IFSS results indicate that laser treatment improves the adhesion strength of UHSPE fibers with epoxy resin because of the changes in surface chemistry and enhanced roughness. The results show the potential of the excimer laser as an alternative surface treatment for fibers to enhance their adhesion with epoxy resins.

The object of this study is to investigate the structure of cast magnesium alloy (Mg-Al-Zn) inoculated with nano particles of different allotropic forms of carbon. The aim of this study is to improve the processability and quality of critical load bearing magnesium alloy part castings. The tasks of the study are: attainment of efficient control of the alloy structural features by introduction of incremental additions of carbon nano particles; determination of the relationship between the quantity of the added inoculating carbon agent and α - solid solution grain size; determination of the influence of allotropic forms of carbon on the morphologic characteristics of the intergranular borders and the eutectoid (a+Mg17Al12); and comparative analysis of the phase composition of the standard ML5 alloy and the experimental alloy ML5 inoculated with carbon black, nanographite, and single-wall carbon nanotubes. The phase composition was determined by X-ray diffraction analysis using copper radiation. Micro X-ray spectral analysis was performed. The following findings were obtained. Using an optical microscope α – solid solution grain size was measured in the standard and inoculated alloy. In the samples of the alloy variants inoculated with 0.1 % wt. of carbon black, nanographite, and single-wall carbon nanotubes, the grain size was reduced by appox. 50 % compared with the standard alloy. In the samples of the alloy inoculated with 0.1 % wt. of nanographite and single wall carbon nanotubes, eutectoid (a+Mg17Al12) precipitates along the grain boundaries were thinner than those in the standard alloy samples and those inoculated with carbon black. X-ray diffraction analysis revealed no new phase formation. The X-ray diffraction patterns of the alloy samples with nanographite and nanotubes display weak peaks of free carbon, which may indicate the presence of free carbon in small quantities in the structure. The scientific and practical originality of the obtained results consists of the following: a technology of inoculation with incremental additions of allotropic forms of nano carbon, namely carbon black, nanographite, and single-wall carbon nanotubes, has been tested on a standard cast magnesium alloy (Mg-Al-Zn system) in an environment similar to the industrial production of critical magnesium cast components. It has been shown that the introduction of nanocarbon in a quantity of 0.1 % wt. can have a beneficial effect on the structural characteristics of ML5 cast magnesium alloy with no change in its phase composition. Nanographite and single wall carbon nanotubes with a regular structure contribute to the formation of thinner intergranular boundaries than amorphous carbon black.

The following paper describes the rationale for Excimer Laser Angioplasty, and discusses the development of a special designed Excimer Laser and catheter system for Laser Angioplasty in femoral and coronary arteries.Methods: A long pulsed (150 ns) Excimer Laser, operating at 308 nm, was evaluated in combination with a special designed silica based catheter system. We used 600 μm single and 6 × 200/6 × 700 μm multiple fiber catheter system to recanalize obstructed canine femoral arteries. The catheter systems were also tested in porcine anormal coronaries. Finally, Excimer Laser Angioplasty was performed in human femoral and popliteal arteries.Results: Using a long pulsed Excimer Laser at 308 nm fiberoptical transmission was excellent, without fiber breakdown. In addition, the catheter systems, especially the multiple fiber system proved to be flexible enough, even for percutaneous intracoronary application. No vessel wall perforation occurred.In 16/18 patients femoro‐popliteal occlusions were successfully recanalized in combination with subsequent balloon angioplasty.Conclusions: Excimer Laser Angioplasty is feasible in man. It increases the number of successful non operative treatments in vascular diseases and might even be an additional surgical tool. Long pulse Excimer Lasers allow easy fiberoptical transmission, and therefore might be favorable.

Zeolite A with waste material: Morphological effect of laser treatments in air

Both holmium (/spl lambda/=2.09 /spl mu/m) and excimer (/spl lambda/=308 nm) lasers are used for ablation of tissue. In a previous study, excimer laser ablation of aorta produced rapidly expanding and collapsing vapor bubbles. To investigate whether the excimer-induced bubble is caused by vaporization of (tissue) water, the threshold fluence for bubble formation at a bare fiber tip in water and on tissue was compared between the excimer laser (pulse length 115 ns) and the Q-switched and free-running holmium lasers (pulse length 1 /spl mu/s and 250 /spl mu/s, respectively). To induce bubble formation by excimer laser light in water, the absorber Oxybuprocaine-hydrochloride (OBP-HCl) was added to the water. Fast flash photography was used to measure the threshold fluence as a function of the water temperature (6-90/spl deg/C) at ambient pressure and as a function of the boiling temperature of water (100-184/spl deg/C) at augmented environmental pressures (1-11 bar). For both the holmium and excimer laser, the threshold fluence for bubble formation decreased proportionally with increasing water temperature (correlation coefficient r=0.95-0.99). Correspondingly, the threshold fluence for bubble formation increased with increasing boiling temperature of water. A similar correlation was found for the excimer laser-induced bubble formation on tissue. Furthermore, for both the holmium and the excimer laser, the threshold fluence for water vaporization was much lower than theoretically predicted values. It is concluded that the principal content of the large (up to 3 mm), short lived ( >

The supersaturated solid solutions of Cr and Ni were formed in (alpha) -Al during laser treatment. Chromium solid solution was formed as a result of doublepass laser treatment of pure aluminum electroplated with chromium. It is reported that Cr distribution along the depth of the melted zone is not uniformal. The concentration of chromium is maximum at the alloy's surface, reducing to zero as depth increases. This data is related to microhardness tests. Ni solid solution was formed as a result of doublepass laser treatment of Al-5% Ni alloy. The distribution of nickel in solid solution is uniformal, but SEM study of the microstructure revealed that solid solution is only formed close to the melted pool bottom.

Auger electron spectroscopy was used to study the composition of the oxides formed on the surface of iron-based alloys under pulsed laser irradiation. Laser treatment in air leads to the formation of a multilayer and multicomponent oxide film on the alloy surface. The upper layer of the oxide film consists of local areas of FeO and Fe2O3 and superoxides (Cr, W, Mo) of the doping elements, while the base for the deeper layers consists of Fe3O4. The laser treatment of tool steels induces a considerable depth redistribution of the doping elements, which affects the composition and depth of the corresponding oxides in the developed film.

A key requirement for the development of commercial fusion power plants utilizing inertial confinement fusion (ICF) as a source of thermonuclear power is the availability of reliable, efficient laser drivers. These laser drivers must be capable of delivering ultra-violet (UV) optical pulses having energies of the order of 5 MJ to cryogenic deuterium-tritium (D/T) ICF targets. Excimer lasers are a leading candidate to fill these demanding ICF driver requirements. However, since excimer lasers are not storage lasers, the excimer laser pulse duration is determined primarily by the length of the excitation pulse delivered to the excimer laser amplifier. Pulsed power associated with efficiently generating excimer laser pulses has a time constant that falls in the range, 30 (tau) <SUB>p</SUB> &lt; (tau) <SUB>pp</SUB> &lt; 100 (tau) <SUB>p</SUB>. As a consequence, pulse compression is needed to convert the long excimer laser pulses to pulses of duration (tau) <SUB>p</SUB>. These main ICF driver pulses require longer, lower power precursor pulses delivered to the ICF target before the arrival of the main pulse. Computer simulations have shown that a `chirped,' self-seeded, stimulated Brillouin scattering (SBS) pulse compressor cell using SF<SUB>6</SUB> at a density, (rho) approximately 1 amagat can efficiently compress krypton fluoride laser pulses at (lambda) equals 248 nm. In order to avoid the generation of output pulses substantially shorter than (tau) <SUB>p</SUB>, the optical power in the chirped input SBS `seed' beams was ramped. Compressed pulse conversion efficiencies of up to 68% were calculated for output pulse durations of (tau) <SUB>p</SUB> approximately 6 ns. Techniques for generating a variety of temporally complex output pulse shapes are discussed.

Studies on laser ablation of silicon using near IR picosecond and deep UV nanosecond lasers

Diblock-copolymers (PS(1700)-b-P2VP(450) or PS(1350)-b-P2VP(400)) forming spherical micelles, can be loaded with a Au-salt and deposited on top of various substrates. Such polymer films have been exposed to a pulsed ArF excimer laser in order to remove the polymer matrix and, in parallel, to chemically reduce the salt into metallic Au nanodots. To analyze this process in detail, it was subdivided into three steps: (a) laser ablation of thick and thin diblock-copolymer films; (b) laser irradiation of Au-salt loaded diblock-copolymer films; and (c) laser irradiation of arrays of metallic Au nanodots. In (a) it was found that a complete removal of the polymer by laser ablation is only possible in air under ambient conditions while identical laser irradiations under vacuum result in a residual layer of approximately 14 nm. Substep (b) revealed a nucleation process of the resulting metallic Au within the micellar core leading to clusters of small Au dots. Furthermore, this substep provided evidence for an asymmetric interplay between the macroscopic temperature of a polymer film during laser treatment and the energy density per laser pulse. In (c) it could be demonstrated that metallic Au nanodots on mica are stable against laser irradiation under conditions leading to a polymer removal.