bluuebunny/crossref_metadata_2025 huggingface dataset:
Soldering with solid state and diode lasers: Energy coupling, temperature rise, process window
Authors: Brandner M. , Seibold G. , Chang C. , Dausinger F. , Hügel H.
Published: September 2010

The increasing number of electrical contacts in automobiles in combination with more complex and miniaturized components leads to higher requirements for the joining technologies. In that context, laser soldering represents an interesting alternative to conventional techniques. So far, solid state lasers [Nd:yttrium–aluminum–garnet (YAG)] and CO2 lasers have been successfully applied in industrial production. Recently, the development of high power diode lasers has offered a new laser source for soldering with technological advantages. Absorptivity of laser radiation on metals, generally increases with shorter wavelength and, consequently, diode lasers may lead to a higher process efficiency compared to Nd:YAG lasers. The absorptivity of copper alloys with different surface conditions has been measured at 808 nm (diode) and 1064 nm (Nd:YAG). When heating up the solder joint, the intensity distribution of the different laser spots becomes important, too. This effect is demonstrated by means of process modeling and temperature measurements for a typical joint geometry. For the case of soldering strip-to-strip joints, the effects of the different energy absorption on the process are pointed out.
Weld strength and process controllability for laser welding of thin sheet metals
Authors: Du J. , Longobardi J. , Latham W. P. , Kar A.
Published: September 2010

Laser welding is a promising technique for joining of thin sheet metal due to its precise heat input control, and the optimized welds should have the desired strength and minimum overheating. The optimum weld depth for maximum weld strength is studied by developing a geometrical model and conducting tensile-shear tests on lap welded thin stainless steel sheets of 100 μm thickness. The results show that to a large extent the strength of lap welds is influenced by the weld geometry. A three-dimensional quasisteady state heat conduction model is presented to predict the weld geometry produced in conduction laser welding of thin sheets under different process parameters. The controllability of weld depth is studied experimentally and theoretically by varying the laser power. A process parameter region has been identified for difficult control of the welding process.
New numerical evaluation techniques for laser processed ceramic substrates
Authors: Murray A. J. , Tyrer J. R.
Published: September 2010

To date laser drilling has not been clearly defined by a standard set of measurement parameters that fully define the features they produce. This article presents criteria for solving some of these issues, which in turn assist in the scientific characterization of the laser drilling process. The measurement criteria presented here fall into four categories: laser parameter, material science, in-process, and geometry measurements. Generation of thermal damage is the Achilles heel of laser processing of ceramics. The fundamental process of laser radiation interaction with ceramic substrates generates a severe thermal gradient between the recast layer and bulk substrate. This in turn leads to the stresses, which cause cracks to form. The numerical quantification of these cracks, in terms of size and distribution, is essential for developing an understanding of how cracks form, and how they can be avoided. It was found that the width of these cracks fell into two discrete size ranges. scanning electron microscope micrographs showed that when the crack width was 7 μm or more, the cracks propagate through the recast layer and into the bulk substrate, significantly weakening the component. These cracks were termed “macrocracks.” The cracks having a width smaller than 7 μm were termed “microcracks,” which were only found in the recast layer, and did not propagate into the bulk material. The numerical evaluation techniques presented here now provide a numerical route for the comparison of strength testing data, with respect to the change in size and distribution of cracking seen in laser processed thermally sensitive materials. This article also presents results from a study in techniques for the quantification of geometry features produced by the laser drilling process. This work employed high/low power optical and electron microscopy, linked with an image processing system, to define these features. The study focused on developing numerical methods for analyzing the surface hole dimensions (diameter, area, shape), and axial hole geometry (cross-sectional area, and material removal rate).
Evaluation of the apparent source in laser safety
Authors: Galbiati Enrico
Published: September 2010

The analysis of the apparent source is used in laser safety to evaluate the retinal hazard. This study provides an analytic method to determine the location and size of the apparent source for laser beams. This method shows that the beam cross section at the center of curvature of the wave front at the eye lens can be considered the apparent source in terms of both the location and size. The approximation given by using the beam waist as the apparent source is examined and the error introduced by this approximation is evaluated. This analysis shows that the beam waist can be considered to be the apparent source only when the distance of the eye from the beam waist is much greater than the Rayleigh length of the beam. Examples showing the location and size of the apparent source are given for different beam characteristics and viewing distances. Measurement methods are also specified to provide an alternative to the analytic method.
Flexural waves generated due to pressure force during the laser induced evaporation process
Authors: Yilbas B. S. , Mahmood F.
Published: September 2010

During the laser ablating of surfaces, the pressure is generated at the interface between the vapor front and the solid substrate. In some cases, the magnitude of the pressure attains considerably high values, which in turn develops a pressure force acting normal to the workpiece surface. The magnitude of the pressure force is sufficient to generate flexural waves propagating along the workpiece. In the present study, a flexural wave generation during laser ablation of steel surface is modeled. The pressure rise at the interface is predicted and the resulting pressure force is determined. The flexural wave characteristics are examined at different locations at the workpiece surface. In order to examine the effect of reflected waves, from the free ends of the workpiece, on the traveling waves radiating boundary conditions on the element sides is considered. It is found that the flexural wave amplitude decays as the location at the surface moves towards the workpiece end. The radiating conditions on the element sides show that the reflected waves have significant effect on the traveling wave characteristics.
Effect of vacuum on penetration and defects in laser welding
Authors: Katayama Seiji , Kobayashi Yoshihiro , Mizutani Masami , Matsunawa Akira
Published: September 2010

The effect of vacuum on weld penetration and porosity formation was investigated in high-power cw CO2 and YAG laser welding. It was consequently confirmed in welding with both lasers that the penetration was slightly deeper in aluminum alloys and austenitic stainless steel with a decrease in the ambient pressure. It was also revealed that no porosity was present in the materials welded at lower pressures. The reason for no porosity formation in vacuum was examined by observing keyhole behavior, bubble and porosity formation situation, and liquid flow in the molten pool during high-power YAG laser welding under various conditions through the microfocused x-ray real-time observation system. It was confirmed in the coaxial Ar or He shielding gas that a lot of bubbles were generated near the bottom part of the molten pool from the tip of a fluctuated keyhole and resulted in large pores. On the other hand, under the vacuum conditions, no bubbles were formed in the melt pool from the keyhole, although the middle and bottom parts of the keyhole swelled up in the molten pool probably because the evaporation of metals was so intense. Moreover, opposite liquid flows as well as different molten pool geometry were observed between the normal atmospheric pressure welding with a coaxial shielding gas and the vacuum welding. Namely, during normal welding in a gas, the circulation of a strong molten flow was observed downward along the keyhole, from the keyhole tip along the bottom molten pool to the upper rear, and subsequently below the surface to the forward keyhole. On the other hand, in vacuum welding, the liquid flowed upwards along the rear keyhole wall, but there was no such strong flow near the bottom and the rear parts of the molten pool. It is considered in vacuum welding that the liquid flow into the bottom part of the molten pool from the keyhole tip does not occur because of the direction of evaporated metals toward the upper keyhole outlet. This may exert a beneficial effect on the reduction or prevention of pores or porosity.
An experimental investigation of the airflow characteristics of laser drilled holes
Authors: Disimile Peter J. , Fox Curtis W. , Lee C. P.
Published: September 2010

When using a laser process for the creation of holes to be used in gas turbine film cooling applications, the mass flow rate is a critical factor in judging hole quality. In the present study, an experimental investigation was undertaken to identify the importance of laser drilling process parameters on the hole airflow. It must be remembered that the total mass flow rate through a hole is a function of the aerodynamic losses resulting from both frictional effects and geometric features of the hole inlet and exit. Optimum aerodynamic performance depends upon the proper selection of laser drilling process parameters. A total of four separate parameters were examined, including laser power, relative laser beam focal position, use of a circular laser beam aperture, and workpiece thickness. Relative laser beam focus was determined to be the most effective individual parameter, followed by workpiece thickness. Laser beam aperture was the least effective parameter. Interactions between the relative laser beam focal position, workpiece thickness, and laser power were found to produce the largest change in the hole flow rate.
Laser machining of glass forming ceramics
Authors: Kirby Kevin W. , Jankiewicz Anthony T.
Published: September 2010

Analyses and results from the laser machining of a cordierite-based (2MgO⋅2Al2O3⋅5SiO2) glass forming ceramics are presented. Three separate pulsed Nd:yttrium–aluminum–garnet laser systems were investigated, including a 2 kW Lumonics Multiwave laser. Efforts were focused on determining the relationship between the laser machining parameters and the resulting depth of cut, residual surface quality, and material removal rate, such that a reasonable level of prediction and optimization could be established. A figure of merit for predicting laser induced microcracking was also resolved. Single pass laser machining rates as high as 1.69 cm3/min and depths of cut as large as 1.27 mm were achieved. Chemical analysis energy dispersive analysis by x ray and microhardness measurements were performed to evaluate sample integrity after machining.
A review of ultrashort pulsed laser ablation of materials
Authors: Shirk M. D. , Molian P. A.
Published: September 2010

The use of ultrashort pulsed lasers in materials processing is an emerging technology. These lasers have the capability to ablate materials precisely with little or no collateral damage, even with materials that are impervious to laser energy from conventional pulsed lasers. The extreme intensities and short timescale at which ultrashort pulsed lasers operate differentiate them from other lasers. The means of ultrashort pulsed laser generation is discussed; included are a survey of pulse compressor techniques with solid state lasers and a brief discussion of excimer-dye lasers. This is followed by a discussion of specific examples of ultrashort pulsed machining of specific materials, along with mechanistic details. Optical breakdown mechanisms, including electron avalanche ionization and multiphoton absorption are discussed. It is shown that as pulse width increases and intensity decreases, laser damage becomes a stochastic process in which the ultrashort pulsed, high intensity light causes optical breakdown over a very narrow range. This, along with the lack of significant thermal conduction, greatly improves the precision of ultrashort pulsed lasers in micromachining applications.
Enhanced imaging of a pulsed Nd:YAG metal vapor plume
Authors: Essien M. , Keicher D. M.
Published: September 2010

Understanding the physical processes that occur in laser material processing is necessary for developing computational models that simulate the laser/material interaction, and for real-time process monitoring and control. This work was performed to gain an increased understanding of the dynamics of the vapor ejected from a metal surface during the laser welding process. The plume is imaged using a laser schlieren technique that detects the refraction of a probe beam. A computer-generated, graded filter replaces the traditional knife-edge schlieren filter, and yields images with enhanced resolution and sensitivity. Images show that intense vaporization begins within the first 10 μs after the laser pulse is incident on the metal surface, and that the vapor propagates as two distinct waves. The first wave is a spherical wave, and is initiated just after the beginning of the laser pulse. For typical laser welding surface intensities, the second, more energetic wave, is initiated approximately 0.6 to 1.5 ms after the beginning of the laser pulse, and propagates away from the surface in a focused trajectory. The results suggest that a simple optical method of detecting the production of a keyhole weld may be performed using laser schlieren imaging.
Survey of bioeffects data and format of standard exposure boundaries
Authors: Wolbarsht M. L.
Published: September 2010

As increasingly more applications of lasers are formulated, the gaps in our quantitative data base of biological data are highlighted. In the past, just as now, research is tied to the need for safety data for specific applications. All too often in the past ambiguity or large disjunctions in the expression of the safety limits were ignored because “nobody uses a laser here anyway.” Such a cavalier attitude is rarely possible anymore as lasers are at all wavelengths and pulse durations, even as in the ultrashort pulse range where only guidelines have been offered to data due to lack of quantitative experimental information. As the gaps in our information are filled, another problem arises. The original formulation of the safety limits was intended more as a backup for the classification scheme, and there were only a few lasers to classify. As only a relatively few experts used the safety boundary equations either to classify new lasers or to deal with applications not easily covered by standard classification schemes, the mathematical formulations of the boundary conditions were not clearly stated and required cumbersome calculations and references to several tables before any correct answer could be determined. The next revision of the American Conference of Governmental Industrial Hygienists and ANSI documents will embody some changes intended to simplify the calculations and make them more rational. Some examples are the use of dimensionally correct equations and decimal exponents.
Workplace exposure during laser machining
Authors: Klein R. M. , Dahmen M. , Pütz H. , Möhlmann C. , Schloms R. , Zschiesche W.
Published: September 2010

Within the EUREKA 643 project “Eurolaser-Safety in the Industrial Applications of Lasers”, the workplace exposure during laser materials processing under manufacturing conditions was determined. Concentrations of airborne pollutants, originating from laser machining, were measured under conditions similar to those encountered in industrial manufacturing processes. A quantitative analysis of the concentrations of airborne substances was carried out using measuring techniques as they are used by the Professional Associations. Selected results of measurements during laser beam cutting of mild steel and stainless steel, welding of stainless steel and zinc coated steel using Nd:YAG and CO2 lasers will be presented. Different production conditions, the efficiency of certain suction systems, and room ventilation systems have been assessed. Also the exposure to chosen chemical compounds during CO2 laser beam cutting of glass-fiber reinforced polypropylene was determined. The results are compared with national exposure limit values and are used for recommendations for the use of laser processing systems in industry and the description of useful protective measures.
Air contaminants generated during laser processing of organic materials and protective measures
Authors: Haferkamp H. , von Alvensleben F. , Seebaum D. , Goede M. , Püster T.
Published: September 2010

As compared to other thermal processes, during laser material processing of organic materials gaseous and particulate emissions are generated. Characteristic for laser-generated air contaminants (LGACs) are the large number of components, the chemical complexity, and the varying emission rates. The characteristics and hazards of these LGACs must be well known, in order to take adequate protection measures to ensure a safe laser workplace and to achieve a high environmental compatibility. Within research projects and the framework of the European project Eurolaser: EU 643 “Safety in the industrial applications of lasers,” emissions have been characterized and medically assessed. Studies show that the quantity, the composition, and the chemical complexity of the LGACs are highly dependent on the laser application, the process parameters and the material processed. Generally, the particles generated are very small and therefore can be mainly respirated. For some plastics, like polyamides, the fume particles are viscous and can easily stick together. The gaseous hydrocarbon emissions usually consist of substances referring to the chemical structure of the material machined, often, the monomers. Aromatic hydrocarbons and polycyclic aromatic hydrocarbons are detected in all cases. Investigations on filter systems show that nonadhesive particles can be filtered efficiently with self-cleaning surface filters; sticky particles, however, cause high pressure loss in the filter and the capture efficiency will rapidly drop. For organic gaseous emissions, no standard filter solution is available. In general, adsorption techniques, catalytic combustion, or biological filtration can be used.
Advances in laser forming
Authors: Magee J. , Watkins K. G. , Steen W. M.
Published: September 2010

Laser forming is fast emerging as a viable means for the shaping of metallic components, as a means of rapid prototyping and of adjusting and aligning. Relevant industry sectors include aerospace, automotive, and microelectronics. In contrast with conventional forming techniques this method requires no mechanical contact and hence offers many of the advantages of process flexibility associated with other laser manufacturing techniques such as laser cutting and marking. This article reviews the mechanisms involved and the main models proposed in laser forming and presents an overview of the main applications currently developed. An assessment is made of the potential for future development of this new technology.
Physics and applications of laser-shock processing
Authors: Fabbro R. , Peyre P. , Berthe L. , Scherpereel X.
Published: September 2010

The first part of this article presents a review of the main process parameters controlling pressure generation in a confined mode. The effect of laser intensity, target material, laser pulse duration, and laser wavelength are, therefore, discussed. An optimized process can then be defined. The second part of this article deals with the surface modifications induced by laser-shock processing. The generation of residual compressive stresses is then highlighted. Finally, in the third part, the interest of laser-shock processing is discussed for several typical applications. A conclusion will present the future trends of this technique.
Precision micromachining with pulsed green lasers
Authors: Chang Jim J. , Warner Bruce E. , Dragon Ernest P. , Martinez Mark W.
Published: September 2010

We have developed high-precision machining based on high-power pulsed green lasers (30–40 ns pulse width) at multi-kHz repetition rate. Dynamics of material removal has been investigated using a copper vapor laser. We found that noticeable surface evaporation starts to appear as laser intensity exceeds 107 W/cm2. Material removal is then dominated by ablation at higher laser intensities. However, strong plasma absorption starts to appear as laser intensity exceeds 2 GW/cm2. This prolongs material heating by hot plasma via electron conduction, resulting in noticeable melt formation and expulsion. Maintaining laser radiance below the plasma-ignition threshold minimizes this melt formation. The optimum rate of ablation on metals was found to be ∼1 μm/pulse with a laser fluence of 50 J/cm2. Higher material removal rate can be achieved at higher fluence, but is mostly accompanied with unwanted melt formation and ejection. By keeping laser intensity within a few GW/cm2, we have demonstrated high-aspect-ratio machining with micron-scale accuracy and negligible heat affected zone. High-quality percussion drilling, trepanning, grooving, and slotting were demonstrated on metals and ceramics with a negligible heat affected zone. Straight holes with sizes varying from 500 to less than 25 μm were consistently drilled with a height-to-diameter ratio up to 40. The high quality machining with scalable machining speed promises expanded use of pulsed green lasers in micromachining.
Risk assessment of light emitting diodes
Authors: Horak Werner
Published: September 2010

Because of increased radiation power and similar hazards, light emitting diodes (LEDs) have been included into International Laser Safety Standards (IEC 825-1): the safety philosophy—developed for point sources—has been transferred to intermediate sources, which are often made for intentional viewing (visible LEDs). The result is an overestimation of the real risk of these kinds of sources. In order to solve these problems, a working group was founded to prepare specific parts of the IEC 825 series with particular application-related requirements. The starting points for actions and the basic safety requirements for these parts are presented.
Ultrashort laser pulse bioeffects and safety
Authors: Rockwell Benjamin A. , Hammer Daniel X. , Hopkins Richard A. , Payne Dale J. , Toth Cynthia A. , Roach William P. , Druessel Jeffrey J. , Kennedy Paul K. , Amnotte Rodney E. , Eilert Brent , Phillips Shana , Noojin Gary D. , Stolarski David J. , Cain Clarence
Published: September 2010

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.
Enhanced methods to get high average power by combining yttrium–aluminum–garnet laser beams and their characteristics in processing materials
Authors: Miura Hiroshi , Fujinaga Shigeki , Narikiyo Toru , Ohmori Akira
Published: September 2010

We investigated two related topics as the first stage of our research: the characteristics of welding with multiple yttrium–aluminum–garnet (YAG) laser beams transmitted through optical fibers and combined at the focal point; and the study of methods of combining YAG laser beams. Each laser beam must be inclined in such a combined system. The plume and the penetration changed their direction from the vertical direction of the specimen to the parallel one of an irradiated beam, if the peak power or energy of the irradiated YAG laser beam exceeds a threshold value. In the two continuous wave YAG laser beams irradiation the form of plume and welding penetration were the same at the average angle of inclination of the two beams of 15° and at typical total power levels as those with a single and vertically irradiated beam to the specimen surface, but were split above the angle of inclination of 30° and total average power of 3.3 kW. Two keyholes would be formed under the split penetration condition. The three split plumes were observed for irradiation by three combined beams. The second stage of our research was the development of an integration optics based on these experiments, which could focus the laser beams transmitted through optical fibers with a condensing lens. We studied all position welding characteristics using the developed integration optics and obtained the result that the overhead welding has the maximum fusion volume among the three orientations—horizontal, vertical, and overhead position welding. The result will be attributed to the direct reach of laser beam to the unfused bottom metal due to the molten metal being pulled down from around the keyhole by gravity. The integration optics is too heavy and large for an articulated robot to hand it and move with high speed. This difficulty comes from combining laser beams at the exit sides of optical fibers. Then, we developed a new launching optics of laser beams at an entrance side of an optical fiber in order to overcome the disadvantage. The development of the launching optics is described.
High power Nd:YAG and CO2 laser welding of magnesium
Authors: Sanders P. G. , Keske J. S. , Leong K. H. , Kornecki G.
Published: September 2010

The laser beam weldability of AZ31B magnesium alloy was examined with high power pulsed Nd:YAG and continuous wave (cw) CO2 lasers. The low solid absorptivity, liquid viscosity, and liquid surface tension of magnesium make it more difficult to weld than steel. Welding parameters necessary to obtain sound autogenous welds were determined for both pulsed Nd:YAG and cw CO2 lasers. The weldability of magnesium was significantly better with the Nd:YAG laser. This observation was attributed to the higher absorption of the Nd:YAG beam, which in turn reduced the threshold irradiance required for welding and produced a more stable weldpool. The signal from an infrared weld monitor was correlated with both the penetration depth and the quantity of black powder on the workpiece after welding. The fine black powder was shown to result from evaporation of magnesium and zinc. The Nd:YAG welds were only slightly softer than the base material and had very narrow heat-affected zones.
Estimation of weld bead size in CO2 laser welding by using multiple regression and neural network
Authors: Park Hyunsung , Rhee Sehun
Published: September 2010

On the laser weld production line, a slight alteration of welding condition changes the bead size and the strength of the weldment. A measurement system is produced by using three photodiodes for detection of the plasma and spatter signal in CO2 laser welding. The relationship between the plasma or spatter and the bead shape, and the mechanism of the plasma and spatter signals were analyzed for the bead size estimation. Penetration depth and bead width were estimated using multiple regression analysis and the neural network.
Cutting performance of a chemical oxygen-iodine laser on aerospace and industrial materials
Authors: Kar Aravinda , Carroll David L. , Latham William P. , Rothenflue James A.
Published: September 2010

A chemical oxygen-iodine laser (COIL) was used for cutting aluminum, titanium, inconel and copper plates. The laser was operated with a stable resonator having an intracavity aperture to produce a circular COIL beam with very few transverse modes. The multimode focal spot diameter was calculated and measured to be approximately 0.24 mm. The new aluminum cut was of good kerf edge quality. These COIL cutting data are compared with an existing theoretical laser cutting model. Using thermophysical data for aluminum, titanium, inconel and copper, this theory agrees very well with the data. To test the versatility of the model, the effects of different assumptions are examined; different assumptions produced very little effect on model predictions at high cutting speeds and a small difference at very slow cutting speeds. Overall, the theoretical model provides good agreement with experiments for a wide variety of metals.
Study on prevention of welding defects in high power CO2 laser materials processing
Authors: Matsumoto Toshifumi , Fukuda Naoaki , Kondo Yasuo , Ohmori Akira , Inoue Katsunori , Arata Yoshiaki
Published: September 2010

For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects. The experimental results demonstrated that the larger the specimen thickness, the more frequently welding defects occur, and that generation of welding defects depends upon the amount of welding heat input. Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the good appearance full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a larger heat input may hinder cooling of molten metal, and need a longer time for metal solidification; in this longer span of time, in-molten metal gas may escape while the metal is sufficiently heated.
Short pulsed laser machining: How short is short enough?
Authors: Chen Xiangli , Liu Xinbing
Published: September 2010

Machined feature quality is examined, and the effects of laser pulse width (and thus peak power or intensity) are investigated for the following four laser systems: (1) a millisecond-class, free-running Nd:YAG; (2) a 100-nanosecond-class, Q-switched Nd:YAG laser; (3) a 100-picosecond-class, mode locked Nd:YAG laser; and (4) a 100-femtosecond-class, Ti:sapphire chirped pulse amplification laser. The effect of shorter laser wavelength is also examined by using the second harmonic wavelength of the Nd:YAG laser in the Q-switched and the mode locked pulse formats. Hole drilling and cutting of superalloy, ceramic, and composite materials are studied. The machined feature quality is improved as the pulse width becomes shorter and the peak intensity becomes higher. The shorter wavelength provides another significant improvement. Finally, an attempt is made to view these quality improvements in the context of process throughput and cost of ownership.
Genetic induction of cultured human cells by high energy, ultrashort pulse laser light
Authors: Obringer John W. , Phipps Steve , Johnson Martin D.
Published: September 2010

The use of laser light for targeting devices and weapons has sharply increased the likelihood that aircrew and support personnel will be exposed to laser light during operations. The increased potential for exposure of humans highlights the need for scientifically based safety standards for laser exposure at the ultrashort pulse lengths. Current safety standards are largely extrapolations of exposure limits at longer pulse lengths using a minimal visible lesion endpoint in the rhesus monkey retinal model. A nonanimal model for assessing laser-light damage to tissue, particularly human, is quite desirous for obvious scientific, political, and fiduciary reasons. We assessed the sublethal insult to human cells using a tissue culture system for specific genes that have been shown to be important in several biological processes that could lead to cancer or cell death. Using the CAT-Tox (L) (Xenometrix, Inc.) assay, it appears that 1064 nm, picosecond pulses of laser light is sensed and induces several stress response genes including RARE and p-53 in a dose dependent fashion. This approach provides insight into a more global methodology for characterizing environmental stressors via genetic profiling.
Microdrilling of metals with ultrashort laser pulses
Authors: Tönshoff H. K. , Momma C. , Ostendorf A. , Nolte S. , Kamlage G.
Published: September 2010

The pulse duration requirements for melting-free and burr-free drilling of metals have been observed in detail. It will be shown that the highest process efficiency and hole quality can be achieved by using pulse durations in the subpicosecond time scale. Furthermore, it will be demonstrated that nonlinear distortions due to high intensities can be successfully minimized by applying diffractive optical elements for beam forming. The influence of the polarization of the laser radiation on the process quality will be discussed. Experimental results will show that the rotation of linear polarized radiation during percussion drilling significantly improves the quality of the hole geometry.
Growth of crystalline ZnO thin films on silicon (100) and sapphire (0001) by pulsed laser deposition
Authors: Lu Y. F. , Ni H. Q. , Ren Z. M. , Wang W. J. , Chong T. C. , Low T. S. , Cheng B. A. , Wang J. P. , Jie Y. X.
Published: September 2010

Zinc oxide thin films have been grown on silicon (100) and sapphire (0001) substrates by pulsed laser deposition. The thin films deposited at different processing parameters were evaluated by x-ray diffraction, Raman spectroscopy, and atomic force microscopy (AFM). The influences of substrate temperature and laser fluence on the properties of the deposited thin films were studied. The full width at half maximum of (0002) x-ray diffraction lines of the films deposited on silicon and sapphire substrates reach a value as small as 0.25° and 0.18°, respectively. The relationship between the intensities of the peaks at 438 and 579 cm−1 in ZnO Raman spectra and deposition temperature were also investigated. Average roughness and surface morphology of the ZnO thin films deposited on Si substrates were evaluated by AFM.
A protocol for eliminating virtually all eye injury accidents in laser products and experimental laser systems
Authors: Carter Howard J.
Published: September 2010

A general design Protocol is proposed to essentially eliminate a major cause of laser injury accidents. The use of protective eyewear for primary protection is discouraged by requiring that systems be designed to be Class I in all operating modes. The Protocol applies primarily to the laser product manufacturer. However, the Protocol may be applied in the laboratory where “open beam” optical systems are being developed. To minimize the likelihood of laser injury accidents in these systems, additional protective rules must be followed. For controlling the injury potential environment, an alternative to the standard operating procedures (which has never been standardized), called a sequence of events, is proposed to support the Protocol application.
Variation of laser induced retinal-damage threshold with retinal image size
Authors: Zuclich Joseph A. , Edsall Peter R. , Lund David J. , Stuck Bruce E. , Hollins Richard C. , Till Stephen , Smith Peter A. , Mclin Leon N. , Kennedy Paul K.
Published: September 2010

The dependence of retinal damage threshold on laser spot size was examined for two pulse width regimes; nanosecond-duration Q-switched pulses from a doubled Nd:Yttrium–aluminum–garnet laser and microsecond-duration pulses from a flashlamp-pumped dye laser. Threshold determinations were conducted for nominal retinal image sizes ranging from 1.5 to 100 mrad of visual field, corresponding to image diameters of ∼22 μm to 1.4 mm on the primate retina. In addition, base line collimated-beam damage thresholds were determined for comparison to the extended source data. Together, this set of retinal damage thresholds reveals the functional dependence of threshold on spot size. The threshold dose was found to vary with the area of the image for larger image sizes. This experimentally determined trend was shown to agree with the predictions of thermal model calculations of laser-induced retinal damage for spot sizes ≳150 μm. The results are compared to previously published extended source damage thresholds and to the ANSI Z136.1 laser safety standard maximum permissible exposure levels for diffuse reflections.
High power diode laser surface glazing of concrete
Authors: Lawrence J. , Li L.
Published: September 2010

This present work describes the utilization of the relatively novel high power diode laser (HPDL) to generate a surface glaze on the ordinary Portland cement (OPC) surface of concrete. The value of such an investigation would be to facilitate the hitherto impossible task of generating a durable and long-lasting surface seal on the concrete, thereby extending the life and applications base of the concrete. The basic process phenomena are investigated and the laser effects in terms of glaze morphology, composition, and microstructure are presented. Also, the resultant heat effects are analyzed and described, as well as the effects of the shield gases, O2 and Ar, during laser processing. HPDL glazing of OPC was successfully demonstrated with power densities as low as 750 W cm−2 and at scanning rates up to 480 mm min−1. The work showed that the generation of the surface glaze resulted in improved mechanical and chemical properties over the untreated OPC surface of concrete. Both untreated and HPDL glazed OPC were tested for pull-off strength, rupture strength, water absorption, wear resistance, and corrosion resistance. The OPC laser glaze exhibited clear improvements in wear, water sorptivity, and resistance (up to 80% concentration) to nitric acid, sodium hydroxide, and detergent. Life assessment testing revealed that the OPC laser glaze had an increase in actual wear life of 1.3–14.8 times over the untreated OPC surface of concrete, depending upon the corrosive environment.
Measurement of temperature distributions during laser cladding process
Authors: Hu Y. P. , Chen C. W. , Mukherjee K.
Published: September 2010

Tungsten–rhenium and platinum–rhodium high-temperature thermocouples have been utilized to measure the thermal cycle and the temperature distributions for laser cladding process. Within optimized operation window, a wide range of processing parameters, and various clad materials have been used in laser cladding experiments. The clad-zone temperatures under various processing conditions fall between 1650 and 1800 °C. These results are in good agreement with those obtained by optical pyrometer.
Continuous wave-Nd: yttrium–aluminum–garnet laser welding of AM60B magnesium alloy
Authors: Pastor M. , Zhao H. , DebRoy T.
Published: September 2010

This study shows that the formation of macroporosity and overfill in the weld pool were the most pronounced problems during continuous wave Nd:yttrium–aluminum–garnet laser welding of AM60B die cast magnesium alloy. The influences of various welding parameters on the formation of porosity and overfill were investigated with particular emphasis on the mechanism and prevention of porosity formation. It was found that the macro pores in the weld pool were mainly formed by the expansion and coalescence of the preexisting pores in the base metal. The amount of macro- porosity in the weld pool could be reduced to approximately that in the base metal by reducing heat input, i.e., by increasing welding speed and decreasing laser power. Increasing the beam defocusing did not reduce porosity in the weld metal until the beam was highly defocused and a shallow weld pool, characteristic of conduction mode welding was obtained. Overfill was observed for deep penetration autogenous welds and its formation could be attributed to porosity formation and the resulting displacement of the liquid metal over the top surface of the workpiece.
CO
2
and Nd:YAG laser beam welding of 6111-T4 aluminum alloy for automotive applications
Authors: Ramasamy S. , Albright C. E.
Published: September 2010

There are two important trends that are currently taking place in the forming of sheet metal into automotive body components. One of these trends is the substitution of aluminum sheet alloys for steel. The other trend is the use of tailor welded blanks. Currently, there exists strong motivation for research to combine these technologies in order to produce tailor welded aluminum blanks. The focus of the current study is to develop welding procedures for autogenous CO2 (continuous mode) and Nd:YAG (continuous and pulsed mode) laser beam welding of 6111-T4-aluminum alloy. The mechanical and microstructural characteristics of the welded joints were evaluated using tensile tests, microhardess tests, optical microscopy, and chemical analysis. Results indicate that this alloy can be autogenously laser welded with full penetration, minimum surface discontinuities and little if any loss of magnesium through vaporization from the fusion zone. The total elongation (all weld metal) in the longitudinal direction for the laser welds made using 3 kW CO2 and 2 kW pulsed Nd:YAG show a decreasing trend with increasing travel speed. Studies indicate that the decreasing trend is probably due to the combination of two factors: orientation of the grains with respect to the loading direction and solidification cracking. The total elongation (all weld metal) of the laser welds made using 5 kW CO2 and 3 kW cw Nd:YAG did not show a consistent trend with travel speed. The main reason for this is solidification cracking. The welds made with 2 kW pulsed Nd:YAG with travel speed between 42 and 63 mm/s displayed the highest total longitudinal elongation (20.78% to 16.45%), compared to the base metal values of 27.8%. A very interesting observation was that the weld surface condition did not have any effect on the ductility of the 6111-T4-aluminum alloy studied in this investigation.
An ion source using laser ablation
Authors: Ooie Toshihiko , Yano Tetsuo , Yoneda Masafumi , Katsumura Munehide
Published: September 2010

This article describes the measurement of the fractional ionization in an ablated plume produced by excimer laser, and the application of the plume as an ion source. Laser ablation of iron, aluminum, and tantalum with a KrF excimer laser was performed in a vacuum chamber. The ablated plume was caught by a cup type electrode used to measure the amount of charged particles as current wave forms. Applying electrostatic potential larger than 40 V, the current wave forms were separated into electropositive and electronegative peaks. Each peak indicates ions and electrons, respectively. The amount of ions, 6×1013 ions/pulse, was estimated by integrating the electropositive peak. The ionization degree of 1.7% was also estimated by a series of analyses. For an aluminum target, the ion current reached 2 A at the peak and 1 mA on average at 60 kJ/m2, 500 mJ, and 50 Hz.
Establishment condition of Scots pine natural regeneration in Tuszyma Forest District
Authors: Dobrowolska Dorota
Published: September 2010

Warunki powstawania odnowień naturalnych sosny zwyczajnej (Pinus sylvestris L.) na terenie Nadleśnictwa Tuszyma
Genetic and silvicultural value of selected grand fir (Abies grandis Lindl.) provenances in Beskid Sądecki
Authors: Kulej Marian
Published: September 2010

Wartość genetyczno-hodowlana wybranych pochodzeń jodły olbrzymiej (Abies grandisLindl.) w warunkach Beskidu Sądeckiego
The influence of admixture and co-dominant species on the height and DBH of silver fir (Abies alba Mill.) and on the growing stock of fir stands in the Carpathian Forest-Natural Region
Authors: Pach Maciej
Published: September 2010

Wpływ gatunków domieszkowych i współpanujących na wysokość i pierśnicę jodły (Abies albaMill.) oraz zasobność drzewostanów jodłowych w Karpackiej Krainie Przyrodniczo-Leśnej
Protection of biodiversity in FSC and PEFC certification systems vs the legal nature protection in Poland
Authors: Referowska-Chodak Ewa
Published: September 2010

Ochrona różnorodności biologicznej w systemach certyfikacji FSC i PEFC a prawna ochrona przyrody w Polsce
Safety and patient comfort with iodixanol: A postmarketing surveillance study in 9515 patients undergoing diagnostic CT examinations
Authors: Häussler Marc D.
Published: September 2010

Background: Iodinated radiographic contrast media are considered safe diagnostic drugs with a low incidence of adverse drug reactions.

Purpose: To determine prospectively the incidence and nature of immediate and delayed adverse drug reactions occurring after administration of iodixanol for contrast-enhanced computed tomography (CT) in routine practice in nonselected patients, and to assess patient comfort (pain and sensations of heat or coldness).

Material and Methods: Patient characteristics (including demographics, risk factors, indication for CT, and status of the vein used to administer iodixanol) and aspects of iodixanol administration (including dose and volume) were documented on a standardized case report form. Patients were asked to report immediate (during the visit) or delayed (occurring up to 7 days after administration of iodixanol) adverse reactions; those deemed related or possibly related to iodixanol were documented on a standardized adverse drug reaction form. Discomfort was rated by patients on a scale of 0–10 for pain, heat, and coldness; individual scores were combined into a composite score (0–30).

Results: Evaluable documentation was provided for 9515 patients in 77 centers across Germany. Adverse drug reactions were reported in 70 patients (0.74%), including hypersensitivity reactions in 55 patients. Thirty patients experienced immediate reactions and 40 experienced delayed reactions. Serious adverse drug reactions were evident in five patients (0.05%). Patients with allergic diathesis appeared to be at increased risk of immediate and delayed adverse drug reactions. Discomfort was generally mild, with 72% of patients reporting a composite score of 0–3.

Conclusion: In the outpatient setting, where it is often difficult to properly assess patients for specific risk factors, it was reassuring that iodixanol demonstrated an excellent safety profile in over 9500 patients undergoing diagnostic CT examinations. There were no unexpected serious adverse drug reactions, and patient discomfort during administration was mild or absent in most patients.