bluuebunny/crossref_metadata_2025 huggingface dataset:
Excimer laser spectroscopy: Influence of tissue ablation on vessel wall fluorescence
Authors: Strebel R. T. , Utzinger U. , Peltola M. , Schneider J. , Niederer P. F. , Hess O. M.
Published: September 2010

Limited steerability and injury to the normal vessel wall are major drawbacks of laser coronary angioplasty. To overcome these limitations a new generation of laser systems has been developed which allows not only to eliminate the atherosclerotic plaque but to guide the laser beam by analyzing the laser induced tissue fluorescence (=spectroscopy) for the treatment of the atherosclerotic vessel. An excimer laser (MAX 10 LP, 308 nm, Technolas, Munich, Germany) was used with an emitting (∅ 1070 μm) and a detecting (∅ 130 μm) optical fiber to induce tissue fluorescence which was analyzed quantitatively by a computerized system. Specimens from the descending (thoracic) aorta were obtained from 24 patients (mean age 68.1 years, range 44–92). Tissue fluorescence was induced with ablating (26–30 mJ/mm2) and nonablating (3 mJ/cm2) laser activations. The emitted fluorescence (range 380–575 nm) was normalized to a wavelength of 380 nm; as a measure of tissue fluorescence the intensity ratio at 500 nm divided by 400 nm was calculated in normal (n=78), mildly atherosclerotic (n=40), and severely atherosclerotic (n=48) tissue samples. Repeated laser activations were carried out and tissue fluorescence was checked until the fluorescence spectrum was normalized. All tissue samples were analyzed histologically by a semiquantitative score. Normal tissue samples showed the highest intensity ratios (5.9±3.4), whereas mildly (2.9±1.3) and severely atherosclerotic (2.1±1.0) samples elicited a significantly reduced fluorescence. Repeated tissue ablations were associated with a normalization of fluorescence intensity ratios in the mildly (7.0) as well as in the severely diseased (4.9) vessels. A curvilinear relationship between intensity ratio and the semiquantitative score was observed (r=0.66) as well as between intensity ratio and intimal wall thickness (r=0.62). No gender related differences were found but there was an inverse relationship between fluorescence intensity ratio and age (r=0.56) as well as between intimal thickness and age (r=0.41). Excimer laser spectroscopy allows reliable detection of atherosclerotic vessel alterations. Fluorescence intensity ratio is inversely proportional to the intimal wall thickness and the severity of the histologic alterations. There is an age dependency of fluorescence intensity ratio which can be explained by an increase in intimal wall thickness. Successful tissue ablation can be obtained by laser angioplasty and allows determination of the optimal point where complete tissue ablation is achieved by laser activation. Thus, excimer laser spectroscopy is an effective method for selective tissue ablation by laser angioplasty.
The indexed assessment of fumes generated by high power laser material processing
Authors: Roach R. J. , Raymond E. A. , Tyrer J. R. , Sharp B. L.
Published: September 2010

The nature of the fume generated by high power laser processing is dependent upon laser type, material being processed, assist gases used, and the energy density required to process the material. The fume produced from any one process will vary in its composition, aerosol size distribution, morphology, and toxicity, all of which are important factors when assessing human and environmental hazards. At present no straightforward method exists to estimate the hazards. In this article a method for indexing the hazards of fumes generated by laser materials processing is presented. The index can be applied to a wide range of materials and laser processing techniques and should lead to a standardization of information pertaining to laser-generated fumes. Two parameters are applied to describe the fumes hazard. The first parameter is the exposure limits, which indicates the perceived hazard of an individual component released during processing. The exposure limits used are the UK long-term occupational exposure standards and the maximum exposure limits. The second parameter is the component production rate from a standard material, i.e., the weight emitted per second (mg/s) of each species during cutting. By combining these parameters, the Normal Air Requirement (NHL) for each component can be calculated. The individual NHLs are then summed to produce an NHLtot. These NHLtot’s serve as guidelines to the hazard since they are highly dependent upon processing criteria and are weighted in this application to particulate emissions. They are also derived from continuous measurements, whereas in real applications the downtime during a working day is considerable. From the NHLtot a classification system can be constructed which can be used to indicate the type of filtration and extraction necessary to effectively deal with the laser processing emissions.
Ray tracing the human eye model to assess injury potential for laser beam configurations
Authors: Carter Howard J.
Published: September 2010

A previously published optical model of the human eye is analyzed with a ray tracing program to test the interaction of various laser beams with the eye. The power density of the focused beam spot on the retina is calculated for each beam image. The injury potential is shown to depend on the accommodation and beam geometry. Suggestions are made to reduce the injury potential for persons aligning optical systems.
Neural motor ocular strategies associated with the development of a pseudofovea following laser induced macular damage and artificial macular occlusion. Is the fovea replaceable?
Authors: Zwick Harry , Ness James W. , Molchany J. M. , Stuck B. E. , Loveday J.
Published: September 2010

Loss of visual acuity following acute photic injury and subsequent recovery is well known. The mechanisms that underlie foveal neural plasticity were assessed in this study. In two patients that recovered to 20/15 Snellen visual acuity following accidental induced foveal damage, contrast sensitivity measurements made under ophthalmoscopic visualization of the retina revealed a preferred retinal location that was superior and temporal to the damaged fovea. This area was used especially for smaller contrast sensitivity targets requiring foveal resolution. Similar preferred retinal location sites were obtained in similar investigations using a Purkinje Eye-Tracker to simulate a small central scotoma. Measures of ocular accommodation obtained in these experiments suggest that a central scotoma may induce an accommodative shift as the oculomotor system shifts to a new PRL for smaller targets that require foveal resolution.
Predictive cathode maintenance of an industrial laser using statistical process control charting
Authors: Katter James G. , Tu Jay F. , Monacelli Lawrence E. , Gartner Mark
Published: September 2010

The performance of a dc-excited transverse-flow CO2 laser welder can be adversely affected by many factors such as electrode arcing, optical contamination, poor maintenance, etc. Many of these factors which occur in production environments are unpredictable, and therefore, difficult to simulate in the laboratory or the laser manufacturer’s facilities. In this article the feasibility of using statistical control charts for laser condition monitoring was demonstrated. In particular, its application for predictive maintenance for the cathode and for verification of the effectiveness of cathode cleaning were investigated. The same approach is readily applicable to other laser components. With more experimental data, optimal control limits can be defined to dictate the maintenance schedule. Future work will include the development of an on-line user-friendly monitoring system that can be used to indicate the condition of the laser and warn the user should any abnormalities be observed. The proposed monitoring system can also be used to determine when and what maintenance is required to keep an industrial laser functioning properly.
Safety recommendations for laser pointers
Authors: Rockwell R. James , Ertle William J. , Moss C. Eugene
Published: September 2010

The use of laser diode pointers that operate in the visible radiation region (400–760 nm) is becoming widespread. These pointers are intended for use by educators while presenting talks in the classroom or at conventions and meetings. They are also useful in any situation where one needs to point out special items during any instructive situation. The pointers can be purchased in novelty stores, mail-order magazines, office supply stores, common electronic stores, and over the internet. The power emitted by these laser pointers ranges from 1 to 5 mW. The potential for hazard with laser pointers is generally considered to be limited to the unprotected eyes of individuals who might be exposed by a direct beam (intrabeam viewing). No skin hazard usually exists. There are, however, even more powerful laser pointers now appearing. The units are imported into the U.S. often without proper manufacturer certification or labeling. The potential for hazards with these devices is not well understood by the general public and workers, and numerous exposure incidents have been recorded by the authors. Users of these products need to be alerted to the potential hazards and be encouraged to follow appropriate safety recommendations. These factors are discussed and safety recommendations for laser pointers are presented.
Safety enclosures for laser cells
Authors: Dahmen M. , Alunovic M. , Kreutz E. W. , Schreiber P.
Published: September 2010

During processing with laser radiation the operator as well as the environment in the vicinity of the laser machine has to be protected against primary and secondary radiation emitted by the process. Up to now there is a lack of information about the resistance and the holding time of frequently used materials for laser guards. Investigations were carried out to yield information about the behavior of several materials under laser irradiation at six wavelengths each representing a type of beam source utilized in industry. The evaluation was guided by the topics fire and health risk, mechanical behavior, damage threshold, and holding time to burnthrough. Tables are created offering a comprehensive survey over the suitability of all materials tested. Recommendations and advice for design and layout of guarding equipment is given.
Development of graded-boundary materials by laser beam
Authors: Kim To Hoon
Published: September 2010

A method to develop graded-boundary materials (GBM) by laser beam is suggested, and its properties and characteristics are discussed. In this method, the differences of laser beam absorptance, thermal expansion coefficient, thermal conductivity, and solid solubility cause difficulties in making ceramic/metal GBM. Meanwhile, the presence of a stepwise compositional profile, the formation of root porosity, and an oblique crack near the boundary region are important in the making of metal/metal GBM by laser beam, and some ways to remove these defects are suggested. As an example, the experimental procedures and results of graded-boundary Alloy 690/steel alloy material produced by laser beam were presented. In this work, the laser surface-alloying method was applied to steel in order to develop a compositional gradient Cr,Ni/steel material. An Alloy 690 sheet was placed on a steel substrate, and then a series of CO2 laser beams were irradiated on that surface in order to produce a homogeneous alloyed layer. Simultaneous compositional gradients of two different kinds of alloying elements (Cr and Ni) were investigated. Sequential repetition of laser surface-alloying treatments up to four times resulted in a fair compositional gradient region with the thickness of about 3 mm from 21% to 0% for Cr, from 40% to 0% for Ni, and from 39% to 99% for Fe in this material.
Laser thermal forming of sheet metal parts using desktop laser systems
Authors: Blake R. J. , Pearson R. M. , Revell A. B. , Simon W. E.
Published: September 2010

The bending of flat sheet metal materials using a laser process is not new to the metals industry. However, refining the process to the point where an angle bend can be predicted is significant when developing prototypes of small and large components [M. Pridham and G. Thomson, Mater. World 2, 574 (1994)]. The methods and process developed to perform this task along with applications of the laser forming process are presented, and key elements to maintain consistency and process repeatability are identified. A 50 W CO2 Desktop laser system provided the controls necessary to create specific shapes from CRES (302) with thickness varying from 0.26 to 0.64 mm. Effects of variations of beam divergence, feed rate, laser power, and pulses per inch, are presented. Material surface condition and material preparation techniques have significant effects on the overall outcome of forming and are therefore discussed. Compound radius bends were performed by calculating the effects of simple bends in conjunction with multiple passes. Experimental data were compiled and a section on the analysis of these data is also presented.
Real-time monitoring of laser beam welding using infrared weld emissions
Authors: Sanders P. G. , Leong K. H. , Keske J. S. , Kornecki G.
Published: September 2010

A nonintrusive, solid-state device has been developed to monitor in real time the infrared emissions during laser welding. The weld monitor output is an analog signal (100–1000 mV) that depends on the beam power and weld characteristics. The dc level of this signal is related to weld penetration, while ac portions of the output can be correlated with surface irregularities and part misalignment or contamination. Changes in dc behavior are also noted for both full and deep penetration welds. Full penetration welds are signified by an abrupt reduction in the weld monitor output. Bead-on-plate welds were made on steel, aluminum, and magnesium with both a cw CO2 laser and a pulsed Nd:YAG laser to explore the relationships between the weld characteristics and the weld monitor output.
Energy requirements for ablation or decomposition of ceramics during CO2 and Nd:YAG laser machining
Authors: Zhang Z. , Modest M. F.
Published: September 2010

In order to assess a priori the outcome of a laser machining process using either simplistic ad hoc or sophisticated models, knowledge is needed of the energy required to remove a unit mass of material. Since laser–material interactions involve vaporization, decomposition, ejection of fragments, plasma initiation, expansion, etc., extrapolating enthalpy data from JANAF tables will result in significant uncertainty. In this article, an experimental setup to measure this “heat of removal” is described. The apparatus mainly consists of an integrating sphere for the sample and a second integrating sphere for reference. The specimen is mounted at the center of the sample sphere, and is heated by a CO2 or Nd:YAG laser, whose beam is split, with a part of the beam going into the reference sphere, to monitor the temporal laser power. The energy reflected by the specimen inside the sample sphere is recorded by a second detector. Combining these data, the total absorbed energy may be deduced. For this type of measurement, energy losses by convection and radiation are generally negligible, while conduction losses may be substantial. In order to minimize conduction losses, the specimens are manufactured to a thickness of less than 500 μm. Still, conduction losses may account for up to 10%–20% of the total laser energy for continuous wave and conventionally pulsed lasers even for such thin samples. Thus, a numerical model is also employed to estimate the conduction losses and to correct the measured value of the “heat of removal.” Experimental data have been obtained for CO2 and Nd:YAG laser irradiation on graphite, hot-pressed silicon nitride, and sintered α-silicon carbide.
Structuring with excimer lasers—experimental and theoretical investigations on quality and efficiency
Authors: Hügel H. , Schittenhelm H. , Jasper K. , Callies G. , Berger P.
Published: September 2010

Manufacturing with excimer lasers is becoming an established technology in microstructuring, drilling, and laser vapor deposition. In this article an overview of the work will be given that was recently performed at the IFSW on excimer laser ablation concerning the quality and the efficiency of the ablation process. In a first part the setup used for the ablation experiments is presented. A beam homogenizer developed at IFSW is explained in more detail. The development of this device was initiated by the need for high beam quality along the whole propagation path. Results with modelings including three-dimensional heat conduction and multiple reflections of the incident beam at the hole walls will be compared with experimental findings. It will be shown that multiple reflections are responsible for the inhomogeneity of the bottom structure and can explain the quality of the ablated structure. Additionally, a few two- and three-dimensional structures obtained by using the presented setup and different working strategies will be introduced. The second part is concentrated on the efficiency of the ablation process. Investigations concerning material vapor expansion in the surrounding atmosphere, and the diagnostic studies of the interaction between this vapor and the incident laser beam during the pulse will be presented. The ablated material vapor/plasma strongly influences the process efficiency due to absorption of up to 80% of the incident laser energy. A model describing the vapor expansion and the interaction mechanisms between vapor, clusters condensed in the vapor, and the laser radiation can explain the decrease of the process efficiency due to absorption of the laser radiation by Mie scattering and inverse bremsstrahlung. The possible influence of the absorption and the material vapor expansion on the deposition of debris and a correlation of the diameter of the area covered with debris with the material vapor luminescence will be given.
Chromatic modulation based acoustic analysis technique for in-process monitoring of laser materials processing
Authors: Lee J. M. , Watkins K. G. , Steen W. M. , Russell P. C. , Jones G. R.
Published: September 2010

The analysis of acoustic waves produced during laser materials processing is widely carried out for characterizing, monitoring, and controlling the process. Traditional methods used in analyzing the acoustic data such as rms signal strength and variation analysis, frequency spectrum analysis are based on signal intensity modulation which offers the advantage of inherent simplicity. However, these basic intensity monitoring systems tend to be sensitive to spurious changes in intensity resulting from variations in the various electrical components within the system and the noise of the industrial environment. In addition, it is known that the acoustic intensity is dependent on the distance and observation angle between its source and acoustic sensor. In this article, a type of acoustic analyzing method based on chromatic modulation is presented. Chromatic modulation offers not only much more acoustic information, precise distinction of the ambiguous signals, and robust monitoring in the laser processing system, but it could also make control of the laser process easier by simple chromatic output factors. It is also shown in this article how a chromatic modulation technique may be utilized as an acoustic analysis method to monitor the laser cleaning process. Consequently, it was found that the chromatic acoustic analysis method could be successfully applied for surface monitoring in the laser cleaning process and could provide correct monitoring information in spite of sensor stand-off variation.
Low level laser therapy wound treatment update
Authors: Sliney David
Published: September 2010

Dr. David H. Sliney participated in the Laser Therapy Session of the meeting, held in the Pallazzo Le Stelline, Milan, Italy on Friday–Sunday, 18–20 June 1999. At the conclusion of his Report Dr. Sliney notes: “Attendance at this meeting was quite interesting. Remarkable benefits continue to be claimed for laser, and even incoherent, light for treating wounds. Despite the fact that those who employ these techniques are impressed with their results, a sound understanding of the underlying photobiological mechanisms of LLLT remain elusive. Highly convincing, objective studies of clinical efficacy which meet all of the demands of the skeptics are required.”
Update of national standard for the safe use of lasers outdoors
Authors: Marshall Wesley J.
Published: September 2010

Lasers are frequently used in an outdoor setting. Guidance is provided in this new draft American National Standard for this use. Unlike lasers used indoors, the user does not have complete control of the space encompassing the entire laser beam since light beams continue until they are stopped by an opaque object. The draft standard discusses proper coordination with local and Federal authorities so that lasers can be used outdoors in a safe manner. The development of the standard was prompted to satisfy both the need by the Department of Defense for a consensus standard, and the need to resolve safety conflicts between the laser light show industry and pilots who would occasionally fly through a demonstration laser beam. The standard has been under development for the past 4 years and publication may be as soon as this year.
New ultraviolet lasers for material processing in industrial applications
Authors: Endert Heinrich , Scaggs Michael , Basting Dirk , Stamm Uwe
Published: September 2010

Ultraviolet (UV) lasers are in many ways ideal industrial processing tools. They offer a noncontact method of producing fine microstructures on many substances, with minimal effect on surrounding material. The most important type of high power UV laser for industrial applications is the excimer laser. Available wavelengths include 351, 308, 248, 193, and 157 nm. The largest commercially available excimer lasers generate up to 200 W stabilized average power and up to 700 mJ pulse energy at 308 nm. Nd:yttrium aluminum garnet (YAG) lasers that utilize nonlinear crystals to transform the 1.06 μm output to its third (355 nm), fourth (266 nm), or fifth (213 nm) harmonic are also an important industrial UV source. More and more diode-pumped, frequency multiplied Nd:YAG lasers greatly impact the industrial processing market. The advantage of this laser is that it is physically compact, highly reliable, and mechanically rugged. Coupled with advantages of short wavelength output, recent improvements in laser reliability, cost of ownership, and performance are enabling UV lasers to be employed in an expanding range of applications. This article will briefly review those applications and their main laser requirements, and then present the most current advances in UV laser technology which address those needs.
Laser beam welding of 5182 aluminum alloy sheet
Authors: Leong K. H. , Sabo K. R. , Altshuller B. , Wilkinson T. L. , Albright Charles E.
Published: September 2010

Conditions were determined for consistent coupling of a CO2 laser beam to weld 5182 aluminum alloy sheet. Full penetration butt and bead-on-plate welds on 0.8 and 1.8 mm sheets were performed. Process conditions examined included beam mode, spot size and irradiance, shielding gas flow, and edge quality and fitup. The observed weld quality variations with the different process parameters were consistent with physical phenomena and a threshold irradiance model. Optimal conditions were determined for obtaining consistent welds on 5182 alloy sheets. Formability and tensile tests were performed on the welded samples. All test failures occurred in the fusion zone. Reduction in formability and tensile strength of the welded samples are discussed with respect to weld profiles and process parameters.
Nd:YAG laser cutting and drilling of PSTZ—Influence of substrate heating temperature on recast layer microcracking
Authors: Murray A. J. , Tyrer J. R.
Published: September 2010

The machining of ceramic components using conventional techniques is slow and expensive due to low yields. High power lasers are capable of machining these materials at far greater speeds. Recast layer microcracking is the Achilles heel of laser processing of ceramics. Techniques for the reduction of the thermal shear caused by laser beam interaction have been investigated. A method for the numerical characterization of microcracking was developed for this work and was based upon scanning electron microscopy image processing. Optimization of the pulsed Nd:YAG laser drilling and cutting cycles enabled repeatable, high quality processing to be undertaken. Heating of the partially stabilized tetragonal zirconia (PSTZ) substrates to high temperatures before and after laser processing was found to reduce the thermal gradients that cause microcracking. Holes with a mean diameter of 679 μm were percussion drilled through the 8.3 mm thick substrates in 0.75 s, and had limited tapering (<150 μm). Single pass, full depth cutting was achieved at a rate of 100 mm min−1. Laser drilling at 1300 °C caused, on average, half the level of microcracking found in the ambient temperature drilled substrates. Laser cutting using the same comparison led to a 6.7× reduction in microcracking. The cutting process overall was found to be less damaging to the ceramic substrates by a factor of 12×. A thermal gradient prediction was used to explain this effect, and was based upon the influence of thermal diffusivity, thermal conductivity, and the effect of the impinging assist gas jet.
Combination of two Nd:YAG laser beams and their welding characteristics
Authors: Narikiyo Toru , Miura Hiroshi , Fujinaga Shigeki , Ohmori Akira , Inoue Katsunori
Published: September 2010

Nd:YAG laser oscillators of two different types were used simultaneously in order to enhance welding ability. A pulse beam emitted from a pulse pumped oscillator was irradiated onto stainless steel (304) together with a rectangularly modulated pulse beam emitted from a cw pumped laser oscillator. The deepest penetration of 7.3 mm was obtained at the total average power of 2.9 kW at a welding speed of 5 mm/s in a bead-on-plate test. It is nearly equal to the penetration depth of 7.7 mm produced by two modulated pulse beams at a total average power of 4 kW. From these results, it can be certified that the pulse beam of high peak power is effective in increasing the penetration depth in two laser beam welding. The plume is extinct after the pulse beam irradiation, although the modulated pulse beam is still irradiated. This phenomenon suggests that the pulse beam effectively enlarges a keyhole, and consequently deepens penetration.
Parametric influence on cut quality attributes and generation of processing maps for laser cutting
Authors: Shariff S. M. , Sundararajan G. , Joshi S. V.
Published: September 2010

Laser cutting is an attractive alternative to conventional cutting methods due to its many inherent advantages. However, notwithstanding its promise for processing diverse categories of materials, the understanding of the subject is incomplete. Although numerous processes are known to significantly influence cutting quality, comprehensive data of practical utility—such as identification of processing regimes to achieve optimum cut surface attributes—remain yet to be generated. The present article establishes a methodology to develop such “processing maps” and illustrates their utility by using laser cutting of mild steel and commercially pure titanium as case studies. The processing maps can be constructed based on any chosen cut quality criteria and can be used to optimize the process on the basis of operational costs. Results reveal that, for achieving good quality cuts, such processing regimes constitute only a narrow region within the wide operating window for mere cuttability and vary substantially with material-assist gas combination. Typically, the operating window for inert gas-assisted cutting is narrower than that for oxygen-assisted cutting involving an exothermic oxidation reaction, which contributes significantly to the overall energy input to the cutting front. The influence of the two major process parameters, laser power and cutting speed, on cut quality attributes such as surface roughness, kerf width, heat affected zone, and cut surface morphology is also discussed in detail. The experimental results have also been compared with theoretical predictions of a scaling law for laser cutting.
Laser cladding
Authors: Vilar R.
Published: September 2010

Laser cladding is a hardfacing process that uses a high-powered laser beam to melt the coating material and a thin layer of the substrate to form a pore- and crack-free coating 50 μm–2 mm thick with low dilution that is perfectly bonded to the substrate. The process may be used for large area coverage by overlapping individual tracks, but it is the ability to protect smaller, localized areas that makes it unique. The wide range of materials that can be deposited and its suitability for treating small areas make laser cladding particularly appropriate to tailor surface properties to local service requirements and it opens up a new perspective for surface engineered materials. Laser cladding processes differ in the way the coating material is supplied. In two-step processes a thin layer of material is deposited on the substrate, for example, as a slurry or a thermally sprayed coating, and subsequently melted with the laser beam. In single-step processes the material is fed continuously into the laser generated melt pool, usually in the form of a powder. Laser cladding by powder injection is superior to alternative processes and is the only one that has found practical use, because it is more energy efficient and it allows for better process control and reproducibility. Laser cladding has found relatively widespread use for the protection of materials against wear, corrosion and oxidation, for the deposition of self-lubricating coatings and thermal barriers, and for the refurbishing of high cost industrial components. Other applications with considerable potential are nonequilibrium synthesis of advanced materials, alloy development and free-form near-net shape manufacturing. Some examples of applications are discussed.
Laser combined medical technologies from Russia
Authors: Zharov Vladimir P. , Latyshev Alexei S.
Published: September 2010

This article reflects the latest achievements of Russian science in the field of creating laser combined technologies for medicine. Lasers and several other therapeutic technologies are shown to supplement each other beneficially and in combination they can provide a significant increase in treatment effectiveness. This review deals with various types of such combinations, i.e., conjunction of laser and ultrasound for treatment of soft and hard tissues; application of acoustic effects for destruction of gall and kidney stones; combination of laser therapy and electrostimulation for treatment of chronic prostatitis; utilization of laser-induced optoacoustic, vacuum, and hydrodynamic effects for transcutaneous drug delivery enhancement; unification of photo- and drug therapy for treatment of inflammatory processes and festering wounds. Experimental and clinical results on combined laser technologies as well as the principles of feedback in complex therapeutic devices which involve optical, thermal, acoustic, and hemodynamic effects are considered. Multifunctional therapeutic micromodules which employ laser combined technologies with both autonomous control and remote feeding are presented.
Pulsed laser deposition of TiN thin film on silicon (100) at different temperatures
Authors: Lu Y. F. , Wang H. D. , Ren Z. M. , Chong T. C. , Low T. S. , Wu X. W. , Cheng B. A. , Zhou W. Z.
Published: September 2010

Titanium nitride (TiN) thin films were deposited on hydrogen-terminated silicon (100) substrates by pulsed laser ablation of a ceramic TiN target (purity: 99.9%). A KrF excimer laser with a wavelength of 248 nm and a pulse duration of 23 ns was used as the laser source. The vacuum chamber was maintained at a pressure of 10−5 Torr during the deposition and the substrate temperature ranged from room temperature to 600 °C. X-ray diffraction, Raman spectroscopy, nanoindentation, and surface profile measurements were performed to characterize the properties of the deposited thin films. The dependence of the hardness, stoichiometry, and crystallinity of the thin films on substrate temperature was investigated. X-ray diffraction measurement showed that the full width at half maximum of the TiN (200) line reached 0.24° at 600 °C. The hardness of the thin films deposited at 600 °C was found to be as high as 26 GPa. The influence of the substrate temperature on the electronic properties of the deposited thin films was studied by Raman spectroscopy. Roughness of the deposited thin films was also investigated.
Lightweight focusing head with fast and compact adaptive mirror
Authors: Huonker Martin , Giesen Adolf , Hügel Helmut
Published: September 2010

Speed and accuracy in three-dimensional laser processing applications, such as cutting and welding of car bodies, is not so much limited by the available laser power or technological problems, but rather by the dynamic accuracy of the processing machines. A decisive step towards a highly dynamic processing machine has been taken with the development of a lightweight focusing head, which is presented in this article. The focusing head is designed as a modular base allowing the integration of various lightweight components. The most important of them are a focusing mirror, a position correction mirror, and an adaptive mirror. The adaptive mirror is used for controlling the axial focus position and the focus radius, respectively. A new approach for a fast and compact, yet lightweight adaptive mirror with a large range of curvature variation and good optical properties is presented.
Laser curing of thermosetting powder coatings: A detailed investigation
Authors: Abhinandan L. , Chari R. , Nath A. K. , Trivedi M. K.
Published: September 2010

Curing of thermosetting powder coating is conventionally done in a convection or infrared oven. Powders requiring 10–15 min at cure temperature in a convection oven reportedly cure within 2–4 min in an IR oven. It has been shown that it is possible to achieve a much faster curing by using a cw CO2 laser. Laser curing has been studied as a function of laser intensity, laser beam size, and interaction time on different substrates. A comparison of laser curing with convection oven curing has been done by studying the results of time–temperature profile, ac impedance, differential scanning calorimetry, and other characterization techniques. The mechanism of laser beam interaction with the powder layer has also been discussed.
Characterization of CO2 and diode laser welding of high carbon steels
Authors: Ng Eng S. , Watson Ian A.
Published: September 2010

Deep penetration welding with a high power CO2 and diode laser may offer an attractive means to join metal for certain applications, for instance: welding car drive shafts and gear plant. The rapid cooling rate of laser welding results in high hardness discontinuities across the welded joint; however, this leads to brittle weld and fatigue failure. To avoid this critical problem, it is useful to optimize the laser operating parameters in order to improve the mechanical properties of the weld. In this study, an experimental analysis was used to predict the significant effect of the weld quality using CO2 and high power diode laser (HPDL) laser welding, operating at 10.6 μm and 810 nm, respectively. Investigations into the weld quality were done to quantify the effect of different welding velocities by examining the hardness profiles, tensile strength, aspect, weld volume formation rate, and microstructure formation. In all cases, the results showed that for the HPDL weld configurations, cracking was observed in the fusion zone, whereas, for a CO2 laser weld, a greater weld strength and wider weld width were observed. For HPDL welding, center-line cracking was found along the fusion zone at higher welding velocities.
Pulsed laser ablation of cement and concrete
Authors: Savina Michael , Xu Zhiyue , Wang Yong , Pellin Michael , Leong Keng
Published: September 2010

Laser ablation was investigated as a means of removing radioactive contaminants from the surface and near-surface regions of concrete from nuclear facilities. We present the results of ablation tests on cement and concrete samples using a pulsed Nd:YAG laser with fiber optic beam delivery. The laser–surface interaction was studied on model systems consisting of type I Portland cement with varying amounts of either fine silica or sand in an effort to understand the effect of substrate composition on ablation rates and mechanisms. The neat cement matrix melts and vaporizes when little or no sand or aggregate is present, and energy dispersive x-ray spectroscopy showed that some chemical segregation occurs in the effluent of ablated cement. The presence of sand and aggregate particles causes the material to fracture and disaggregate on ablation, with particles on the millimeter size scale leaving the surface.
Thermochemical modeling of oxygen-assisted laser cutting
Authors: Espinal Dayana , Kar Aravinda
Published: September 2010

A simple mathematical model is developed to relate kerf depth to laser power, laser scanning speed and kerf width during laser cutting. The model is based on a lumped parameter technique in which the overall energy balance is considered. The energy released during the chemical reaction between the material that is being cut and the assist gas is considered for oxygen-assisted cutting. Experiments were conducted using a carbon dioxide (CO2) laser to test the significance of the chemical reaction in the cutting process. The experiments conducted consist of cutting stainless steel using nitrogen as an inert assist gas, and the cutting of stainless steel using oxygen as a reactive assist gas. The cutting data between the two experiments are compared and used to demonstrate the scaling of the mathematical model. Oxygen increases the cut depth significantly compared to when nitrogen is used as an assist gas.
A system for on line monitoring of pulsed laser welding processes
Authors: Charton S. , Voisin Y. , Gorria P. , Vauzelle T.
Published: September 2010

In the field of laser welding, the lack of suited inspection means generally leads users to develop their own systems. From this observation, an adaptable system to all welding conditions, dedicated to on line inspection of pulsed laser welding operations, has been devised. Its principle is very close to Quality Control by Artificial Vision systems. It is based on the recording and the treatment of signals resulting from laser–material interaction. The use of classification techniques and signal processing tools such as the wavelet transform, introduce an innovating approach of on line inspection. Thus, defects detection by discriminant parameters determination becomes automatic and nonsubjective. The presented method allows to determine the weld spot position (pulse number) and the type of defects and to estimate the reliability of the detection. This article presents the principle of the system and its validation on some classical defects in laser welding. The final objective is, in particular, to detect penetration variations during welding hollow parts, at the Valduc center of the French Atomic Energy Agency. In most cases penetration can be easily estimated by observing (with a photodiode or charge-coupled camera for example) the heating of the back of the welded part. Unfortunately in case of hollow parts, the sensors can only be placed at the outside!
Design criteria for flexible safety barriers used in industrial laser environments
Authors: Hemmerle Ryan , Rockwell R. James
Published: September 2010

The requirements of ANSI Z136.1 (Sec. 4.6.4) specifies that a blocking barrier, which can block or filter the laser beam at the entryway should be used inside the controlled area to prevent the laser light from exiting the area at levels above the applicable MPE level. This article examines methods of installation and design of these laser barriers, including screens and curtains. The concept of when to use a ceiling mounted barrier versus a floor frame barrier as well as the benefits and drawbacks of each design is also discussed in this paper. Testing criteria is also addressed in terms of damage threshold of the barrier material itself as well as a review of how and when to incorporate specific window filter material. Specific labeling, indicating the damage threshold levels are also addressed. Other requirements for laser safety barriers will also be discussed such as materials used in the manufacture of laser barriers. The Z136.1 mentions (Appendix C2.4), “Important is the factor that decomposition products resulting from the laser interaction not be a respirable hazard. Material safety data sheets are also discussed as well as testing methods to determine respirable hazards.
Initiation and termination phenomena in laser welding of aluminum
Authors: Forsman T. , Kaplan A. F. H. , Powell J. , Magnusson C.
Published: September 2010

This article investigates a defect problem related to laser welding of tailored aluminum blanks. During the initial few millimeters of welding the weld was intermittent. By applying an analytical line source model the weld was shown to experience overheating close to the starting edge. This overheating was reduced by ramping the power during the initial 100 mm and this made the defects disappear.
Dynamical description of the keyhole in deep penetration laser welding
Authors: Fabbro Remy , Chouf Karim
Published: September 2010

We study the keyhole geometry as a function of the main operating parameters such as welding speed, laser incident intensity, or sample material. This model is based on a drilling velocity whose combination with the welding velocity causes the inclination of the front keyhole wall (FKW). This front inclination is shown to be stationary and stable all along the FKW. The penetration depth results from the product of this drilling velocity and a characteristic time defined as the beam diameter divided by the welding speed. By using a ray-tracing procedure, the dynamics and the complete keyhole geometry can be determined by taking into account the multiple reflections inside the keyhole and a description of the closure process of the rear keyhole wall (RKW). We show that this RKW cannot be stationary all along its surface and only an adequate laser intensity distribution can make it stationary. The interest of elongated focal spots or twin spots is then demonstrated. At high welding velocity the front wall is inclined and is composed of several layers resulting from the successive reflections. The rear wall fluctuates around an apparent equilibrium, and corresponding fluctuations occur at maximum penetration depth.
Free-form laser consolidation for producing metallurgically sound and functional components
Authors: Xue L. , Islam M. U.
Published: September 2010

Functional metallic components can be built layer by layer from a computer-aided design model, by using an optical fiber coupled Nd:YAG laser beam along with the simultaneous delivery of desired metal/alloy powders through a nozzle into the molten pool. Building of shapes using various alloys, including 316 L stainless steel, Ni-base IN-625 superalloy, and M4 tool steel, have been investigated. The components built using the free-form laser consolidation are metallurgically sound, free of cracks and porosity. Surface finish on the order of 1–2 μm (Ra) can be obtained on the consolidated samples. The microstructure of the laser-consolidated samples is similar to the rapidly solidified materials. Under certain conditions, directionally solidified microstructure can also be obtained. X-ray diffraction analysis reveals that laser-consolidated material maintains the same phase structure as the original powder. The tensile properties of the laser-consolidated IN-625 alloy and 316 L stainless steel are comparable to the respective wrought materials. The microhardness of the consolidated M4 tool steel reaches to approximately Hv 1000. The polarization testing results indicate that laser-consolidated IN-625 alloy and 316 L stainless steel show a similar corrosion resistance as the respective wrought material in 3.5% NaCl solution.
Laser surface alloying of silicon into aluminum casting alloys
Authors: Xu Zhiyue , Leong Keng H. , Sanders Paul G.
Published: September 2010

Aluminum alloys that are easily castable tend to have lower silicon content, and hence, lower wear resistance. The use of laser surface alloying to improve the surface wear resistance of 319 and 320 aluminum alloys was examined. A silicon layer was painted onto the surface to be treated. A high power pulsed Nd:yttrium–aluminum–garnet laser with fiber-optic beam delivery was used to carry out the laser surface treatment to enhance the silicon content and produce a very fine silicon-rich phase. One advantage of using a pulsed laser beam to carry out the surface alloying is it provides a vigorous turbulence in the molten pool and enhances the dissolution of the fine silicon into the molten bath and its dispersal in a short process time. Process parameters were varied to obtain smooth single treated tracks and minimize the surface roughness from overlap of the treated tracks. Our goal is to take advantage of the vigorous turbulence characteristic of the pulsed beam to obtain desired microstructure of laser-alloyed layers, and at the same time to employ the pulse parameters that mimic continuous wave operation as closely as possible to produce the smooth surface. The surface-alloyed layer was characterized and the silicon content and microhardness profile were determined.
Laser remelting of plasma sprayed coatings
Authors: Wang K. L. , Zhu Y. M. , Steen William M.
Published: September 2010

The effect of laser remelting on the microstructure and corrosion resistance of cobalt based and nickel based alloy plasma sprayed coatings has been investigated. The results show that coating microstructure and density are markedly improved by laser melting and much better chemical homogeneity is obtained. The microhardness and corrosion resistance of the coatings are also enhanced significantly following laser melting.
The Mobile Edition: JOSPT to Go!
Authors: Simoneau Guy G.
Published: September 2010

The editorial announces JOSPT's new mobile edition and describes the features of the mobile website.

J Orthop Sports Phys Ther 2010;40(6):334–335. doi:10.2519/jospt.2010.0106
The Feasibility and Acceptability of Using a Portfolio to Assess Professional Competence
Authors: Miller Patricia A. , Tuekam Rosine
Published: September 2010

Purpose: Little is known about physical therapists' views on the use of portfolios to evaluate professional competence. The purpose of this study was to gather the opinions of physical therapists on the feasibility and acceptability of a portfolio prepared to demonstrate evidence of clinical specialization through reported activities and accomplishments related to professional development, leadership, and research.

Methods: Twenty-nine Canadian physical therapists practising in the neurosciences area were given 8 weeks to prepare a professional portfolio. Participants submitted the portfolio along with a survey addressing the preparation of the portfolio and its role as an assessment tool. Qualitative content analysis was used to interpret the participants' comments.

Results: Participants reported that maintaining organized records facilitated the preparation of their portfolio. They experienced pride when reviewing their completed portfolios, which summarized their professional activities and highlighted their achievements. Concerns were noted about the veracity of self-reported records and the ability of the documentation to provide a comprehensive view of the full scope of the professional competencies required for clinical specialization (e.g., clinical skills).

Conclusion: The study's findings support the feasibility and acceptability of a portfolio review to assess professional competence and clinical specialization in physical therapy and have implications for both physical therapists and professional agencies.