Mechanical laser ablation

Laser ablation systems hold considerable promise if restenosis (reblocking of the arteries) rates are reduced. The rate as of 1995 is 30%, typically within six months. Mechanical or atherectomy devices to cut, shave, or pulverize plaque have been tested extensively in coronary arteries. Some of these have also been approved for peripheral use. The future of angioplasty, beyond the tremendous success of conventional balloon catheters, depends on approaches that can reduce restenosis rates. For example, if appHcation of a dmg to the lesion site turns out to be the solution to restenosis, balloon catheters would be used for both dilating the vessel and deUvering the dmg. An understanding of what happens to the arterial walls, at the cellular level, when these walls are subjected to the various types of angioplasty may need to come first. 

Laser ablation of polymer films has been extensively investigated, both for application to their surface modification and thin-film deposition and for elucidation of the mechanism [15]. Dopant-induced laser ablation of polymer films has also been investigated [16]. In this technique ablation is induced by excitation not of the target polymer film itself but of a small amount of the photosensitizer doped in the polymer film. When dye molecules are doped site-selectively into the nanoscale microdomain structures of diblock copolymer films, dopant-induced laser ablation is expected to create a change in the morphology of nanoscale structures on the polymer surface. 

As aforementioned, laser ablation of polymer films themselves and dopant-induced laser ablation of polymer films have been extensively investigated. The photochemical or photothermal mechanism has been discussed. The feature of the dopant-... 

Fukumura, H. and Masuhara, H. (1994) Xhe mechanism of dopant-induced laser ablation. Possibility of cyclic multiphotonic absorption in excited states. Chem. Phys. Lett., 221, 373-378. 

Hiroshi Fukumura received his M.Sc and Ph.D. degrees from Tohoku University, Japan. He studied biocompatibility of polymers in the Government Industrial Research Institute of Osaka from 1983 to 1988. He became an assistant professor at Kyoto Institute of Technology in 1988, and then moved to the Department of Applied Physics, Osaka University in 1991, where he worked on the mechanism of laser ablation and laser molecular implantation. Since 1998, he is a professor in the Department of Chemistry at Tohoku University. He received the Award of the Japanese Photochemistry Association in 2000, and the Award for Creative Work from The Chemical Society Japan in 2005. His main research interest is the physical chemistry of organic molecules including polymeric materials studied with various kinds of time-resolved techniques and scanning probe microscopes. 

Photo/Thermal Reactions. The fifth basic class of photopolymer chemistry that can be used in commercial applications is based more on physical changes in a polymer-based matrix than on chemical reactions. A recent application of this technology is the laser ablation (77) of an organic coating on a flat support to directly produce a printing plate. The availability of newer high energy lasers will allow more applications to be based on the photo/thermal mechanism. 

In the present work, we have examined poly(N-vinylcarbazole) (abbreviated hereafter as PVCz) and pyrene-doped poly(aethyl methacrylate) (PMMA) films by using a tine-resolved fluorescence spectroscopic aethod. Fluorescence spectra and their dynanic behavior of the forner fila were elucidated with a high intensity laser pulse and a streak camera, which nakes it possible to neasure dynaaics just upon laser ablation. This aethod reveals aolecular and electronic aspects of laser ablation phenomena (17). For the latter fila a laser pulse with weak intensity was used for characterizing the ablated and Basked areas. On the basis of these results, we demonstrate a high potential of fluorescence spectroscopy in aolecular studies on laser ablation and consider its mechanism. Experimental... 

Si - Si Annihilation and Ablation Mechanism. The Si - Si annihilation process is responsible to laser ablation, which was supported by the following experiment. Total fluorescence intensity and the relative intensity of excimer emissions (-15 72 ns gate width) were plotted against the fluence in Figure 3. It is interesting that the relative contribution of excimers showed a similar change to that of total fluorescence intensity. This indicates that the Si - Si annihilation has an important role in the primary processes of laser ablation phenomena, since the relative contribution of excimers is determined by the degree of Si -Si annihilation, and the suppressed fluorescence intensity corresponds to the enhanced ablation. 

Laser ablation of TiC targets was studied by De Maria et al. (1997). TiC films were realized on oriented [111] silicon. During ablation the chamber was kept under a dynamic vacuum (1.5 10 4 Pa) the laser fluence was varied in the range 0-15 J/cm2. Different ablation mechanisms, corresponding to different film characteristics, were observed related to the laser fluence values. At low fluence values (0-3 J/cm2), a film of composition TiC2 was obtained. Films obtained at 3-8 J/cm2 showed a composition close to TiC they had the best characteristics of composition, crystallinity and compactness. 

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

ICP-AES was validated for the simultaneous determination of Al, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Se, Sr and Zn in human serum in a clinical laboratory. The samples underwent digestion and yttrium was used as an internal standard. The LOD were as follows 0.002-0.003 (xM for Ba, Cd, Mn and Sr 0.014-0.07 (xM for Be, Co, Cr, Cu, Fe, Li, Ni, Pb and Zn and 0.2-0.9 (xM for Al, B and Se. The concentrations of Al, Be and Co in human serum were found to be above the LOD, while those of Cd, Cr, Ni and Pb were below the LOQ however, in case of acute intoxication with the latter elements the method is valid . Matrix effects were evaluated for ICP-AES analysis using solution nebulization and laser ablation (LA) techniques. The main matrix-related interferences stem from elements with a low second ionization potential however, these are drastically reduced when pure He is used as carrier gas. This points to Ar (the usual carrier) participation in the interference mechanism, probably by interacting with doubly charged species. ... 

Considering the low separation energy between the 3A" and A states, the hypothesis that, in the reaction of laser-ablated Ti. TiO and Ti02 with CO, the excited JA state can be generated, becomes plausible. This is consistent with the B3LYP results for the PES of the insertion mechanism of Ti into the C-0 bond of carbon dioxide, which shows that no barrier is necessary for this process, in agreement with the experimental indication [49],... 

The past decade has led to the detection of new carbon allotropes such as fullerenes26 and carbon nanotubes,27 28 in which the presence of five-mem-bered rings allows planar polycyclic aromatic hydrocarbons to fold into bent structures. One notes at the same time that these structures are not objects of controlled chemical synthesis but result from unse-lective physical processes such as laser ablation or discharge in a light arc.29 It should be noted, on the other hand, that, e.g., pyrolytic graphitization processes, incomplete combustion of hydrocarbon precursors yielding carbon black, and carbon fibers30 are all related to mechanisms of benzene formation and fusion to polycyclic aromatic hydrocarbons. 

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