Thousands of laser systems are employed profitably in a variety of industrial applications. These installations have proved successful for economic and technical reasons. And, in certain applications: ceramic scribing, resistor trimming, sheet metal cutting, and air foil drilling, for example, have become the industry standard. Most of these installations are free standing or, at best, part of an off-line manufacturing cell. Examples of laser systems fully integrated into a production line, where the laser process is synchronized with up and down stream manufacturing operation, are rare. The laser has been under utilized in its potential contribution to production line productivity. Current development in laser beam delivery: multiplexing, beam splitting and other distributed energy concepts make the laser an attractive option for just-in-time manufacturing operations. The reasons for this apparent neglect of the laser's full potential are reviewed in this paper, and suggestions for improvement of this situation are offered. Examples of fully integrated laser systems and their successful implementation are described and a forecast of changes in the way lasers contribute to improved productivity and profitability will be made.

Beam guidance of high power YAG-laser (cw, pulsed, Q-switched) with average powers up to 2000 W by flexible glass fibers facilitates the integration of the laser beam as an additional tool into metal cutting machines. Hence, technologies like laser cutting, joining, hardening, caving, structuring of surfaces and laser-marking can be applied directly inside machining centers in one setting, thereby reducing the flow of workpieces resulting in a lowering of costs and production time. Furthermore, materials with restricted machinability--especially hard materials like ceramics, hard metals or sintered alloys--can be shaped by laser-caving or laser assisted machining. Altogether, the flexibility of laser integrated machining centers is substantially increased or the efficiency of a production line is raised by time-savings or extended feasibilities with techniques like hardening, welding or caving.

In 20 years laser welding of sheet metal has been demonstrated as a possible high-tech metal joining process. However, the major obstacle to the introduction of laser welding in for example car body manufacturing has been and is the fixturing problem. In case of laser butt welding of 0.5 - 1 mm thick steel sheets, the maximum acceptable gab between the sheets to be welded is in the range of 40 - 50 micrometer. Out of this demand two major problems arise: (1) the high precision required in weld preparation in terms of precise shape of the two sheets to be welded. (2) the problem of maintaining a narrow gab under welding, where thermal distortions, even though they are relatively small in this process, still will open the gap as the welding beam proceeds along the seam. In this paper a unique technique to overcome these problems will be described. The results of the experimental work described in this paper demonstrates the technique in 2D welding, where high quality butt welds has been demonstrated with virtually no clamping forces applied by utilizing a special seam preparation technique. Possibilities in car body manufacturing and other 3D sheet metal assembly by means of the flexible laser welding technique will be discussed.

High-contrast selective deposition of copper (Cu) and gold (Au) thin films using succeeding plating processes after the KrF excimer laser direct doping is described. Contrast ratio of selective deposition is estimated to be 10⁸ for gallium arsenide (GaAs). As the properties of the deposition, resistivity of deposition and contact resistance to semiconductor are studied. A submicron line-pattern is formed by KrF excimer laser projection direct doping. Cu thin films are deposited selectively on the doped region by electroplating using a CuSO₄ aqueous solution. For Au, the electroless plating using a commercial Au-24s solution has been carried out. The low specific contact resistance of 4.95 X 10^-6 (Omega) cm² between Au and GaAs which is 1/150 as small as that of the conventional alloyed contacts is achieved.

The technique of laser beam alloying combines the benefits offered by high levels of laser beam energy and spot-on positional accuracy to treat the areas of forming tools most prone to wear. All compression molding and hammering tools stand to benefit from this application. Tools made of any of the hot forming tool steels currently in standard industrial use are suitable candidates for this treatment. The advantages of die forging, i.e. optimum material utilization, high productivity and low unit labor costs are offset to a certain extent by relatively high tool costs. The potential of alloying in the manufacture of wear-resistant tool steels has been largely exhausted. Increasingly, attention is focusing on surface treatment techniques. The scope for improving the efficiency of forging tools using conventional hot treatment and hard facing processes is, however, marginal. Due to insufficient thickness and adhesive strength of the coating, thin film technologies are generally unsuitable for coating tools which are subjected to high levels of thermal and mechanical strain. In contrast, the application of various laser surface techniques to forging tools in order to prolong tool life is highly promising.

The use of flexible manufacturing laser systems for surface treatment applications in different production areas, is sometimes the unique mean to reach the competitive degree required by the present market subjected to rapid evolution. The diffusion of laser surface treatment evidently depends on the diffusion of flexible manufacturing systems, and this depends also on the disposability of such technologies able to make the system technically and economically advantageous; moreover strongly innovative techniques are required which can easily be integrated in an automatic and flexible process. In the heat treatment field, traditional techniques often show heavy limitations for the use `on-line' in a manufacturing process. Heat treatment, in fact, are often carried out off-line; consequently the components, after mechanical machining, must be transported to the heat treatment shops, and afterwards they are carried back again to the machining line, for the finishing operations. Laser technology allows selectively surface treatment directly on production line with consequent high reductions in times and costs.

High-power beam processes can be used for the surface treatment of metals (hardening, remelting, alloying, coating, etc.). Both the laser and the electron beam are occasionally being used at the moment. Whereas high flexibility is a definite advantage of lasers and electron beams over conventional processes, disadvantages include high costs and, especially for lasers, limited output power. As an alternative to these high-power beam technologies, the Laser Zentrum Hannover has developed an alternative beam process for surface treatment using a high-power light source. A comparison of arc lamps with lasers for surface treatment shows that light sources have advantages: a lower investment due to a simple set up, a high maximum power output of 50 kW, a large maximum track width, easy workpiece preparation, as no absorption enhancing coatings are necessary, and simple operation and maintenance. Disadvantages are the limited flexibility and accessibility regarding workpiece geometry and beam size, and the limited beam power density of 3500 W/cm². Investigations are carried out for hardening steel 90 MnVCr8 and remelting spheroidal cast iron GGG 60 with beam power up to 46 kW, and different track widths from 5 - 120 mm. For steel, an edge hardness of up to 1000 HV0.2 was achieved, which was kept constant across nearly the whole surface, using the self quenching effect. For hardening without surface melting, maximum hardness depths of 3 mm were obtained. By remelting cast iron, hard ledeburitic edge zones up to 2.5 mm thick are formed, which show a nearly homogeneous edge hardness of about 900 HV0.2.

Laser processing can show its full capacity in the applications in which the laser is not hindered by the constraints imposed when the laser is inserted in conventional systems without reassessing the overall system design. In these cases the laser process performance up to now was kept at very low levels because conventional systems would not need nor accept higher ones. Instead now said performance must be brought to the upper limits inasmuch as the lasers will be the pacesetter for the performance of the new systems freed from all the old design bondages. `Augmented' laser multiprocessings obtained by combining the laser with conventional processes in a manner which take advantages of unexpected synergies permitted by the laser, allow the system to outperform, in all aspects from productivity to quality, the already much higher performance of dedicated all laser multi processing systems. Most important `augmented' laser multi-processing is the cut-bend-weld. At present one of the dedicated laser multiprocessings of greatest interest is the laser cut-weld. To obtain the best benefits and then to step up to `augmented' multiprocessing is necessary to improve and master each of the two processes, but under a radically different system design perspective, that is considering the combination among themselves, that with other laser and conventional processes, and that with the handling and jigging subsystems, always looking for interactions, synergies and false constraints.

A pilot 3D-laser machining system for combined laser beam cutting and welding of complex tube geometries with small diameters ((phi) < 20 mm) was developed. It consists of a pulsed Nd:YAG-laser, rated 500 W, two fiber beam deliveries each equipped with a special working head, a tool changing system, an articulated robot, a turn table and the necessary clamping systems all housed in a protection cabin. A processing strategy was developed resulting in subsequent oxidefree cutting and welding in one clamping device to reach the tolerable gap widths for laser welding without filter material. The system performance was evaluated concerning repeatability, reliability and laser safety. The performance of laser manufactured workpieces show a better quality than those produced by conventional welding. Economical aspects are given in comparison to conventional welding.

Increasing productivity in splitting up of metal sheets by means of mechanical cutting processes is today limited by long change-over times as well as nonproductive times and insufficient quality caused by tool wear. In the case of high-quality materials even a slight quality reduction concerning development of dross attachment and induced stress leads to a lot of rejects. In order to increase the cutting speeds within a range economical for industrial use, i.e. about 100 m/min, a completely new type of laser cutting process had to be developed. As opposed to conventional laser cutting, during which a semicylindric cutting front is formed, a closed keyhole with subsequent melt film ejection is produced during the completely new laser cutting process. The incoupling of energy no longer only results from pure surface absorption but in addition from plasma formation and multiple reflection. With the help of the wear resisting tool `laser' the cutting quality is constantly good and can even be significantly improved in comparison with the conventional cutting method with circular knifes. In the case of a sheet thickness of 0.2 mm grain oriented electrical steel can be cut e.g. with a cutting speed of 130 m/min, aluminum with 270 m/min, copper with 95 m/min and zinc with 280 m/min; the necessary laser power is 1300 W. Based on the results of basic research the prototype of a laser slitting line was constructed and went into operation in autumn 1991. Up to now various materials for different customers have been cut on this slitting line and used in industry. Especially when cutting grain oriented electrical steel, which is a material with very high requirements on the cutting process, it becomes evident that the laser cutting process compared with the conventional technique has considerable advantages concerning cutting quality and quality assurance.

The quality of laser material treatment processes depends to a large extent on an adequate power density profile at the workpiece. Stable and controlled beam propagation properties are necessary conditions for improved applications. To enhance the profitability of the processing techniques, it is useful to enlarge the range of possible combinations between lasers and multiple workstations. A multiplexing beam guiding system with equipped beam expanders is presented that permits the flexible use of various workstations and laser sources as well as time-sharing operations. The propagation properties of laser sources with different beam propagation factors have been measured, and, in particular, the influence of apertures is shown. To improve the flexibility, a system has been developed and installed that combines two flexible beam expanders using adaptive copper mirrors. It allows to control both the focus radius and the focal position, simultaneously and independently from each other. Numerically simulated data as well as experimental results are presented demonstrating the capability of this system. Using typical focusing optics, a focus shift can be realized up to 10 mm and the focus radius can be varied up to 100%. The combination of two individual 5 kW laser beams to be simultaneously applied on a specific workstation is presented. A special focusing device allows an independent variation of the focal conditions of each laser beam. By this procedure, the available laser power can be increased and a wide variety of space and time dependent intensity distributions is achievable. Their implications on process improvements will be discussed, briefly. The presented examples concerning welding and cladding demonstrate substantial yields in both efficiency and quality.

The properties of phase retarders for high-power laser irradiation based on metallic diffraction gratings with various profile parameters are investigated both theoretically and experimentally. High energy efficiency of linear-polarized light transformation into the elliptically-polarized specular-reflected wave is achieved at the resonance excitation of surface electromagnetic waves. The nonselective phase retarders on the base of `deep' gratings for various wavelengths and shift values were also designed, and effectivity of their application for metal cutting with high-power CO₂-lasers was demonstrated.

Results are presented of an experimental investigation into various beam sampling and monitoring techniques applicable to high power laser systems. A hole matrix mirror displayed good sampling fidelity, and power handling capabilities in excess of 10 kW have been demonstrated. A holographic beam sampler displayed poor spatial fidelity in the sampled beams. The transmission leakage through a dielectric high reflector was shown to be an unreliable method of beam sampling due to non-uniform transmission characteristics. Phase profiles of beams with various aberrations have been recorded using a self referencing Mach Zehnder and a point diffraction interferometer. The results show a good correspondence with interferograms of the same aberrations obtained conventionally. The applicability of these devices to particular laser types in industrial environments is discussed.

The use of high power CO₂ lasers for various applications in material and production technologies has increasingly grown, and new applications are on their way to being used in industry. Due to varying beam path lengths, proper beam delivery is essential to obtain constant working conditions when using machines with moving beam guidance. The focussing characteristics of divergent laser beams change with the distance between laser source and processing head. To keep the energy distribution on the workpiece surface on the same level while working with flying optics, the use of deformable mirror systems has proven to be a suitable solution. In this case, a newly-developed system is brought into the beam guidance system to keep the focal spot diameter constant. As far as applications are concerned, where the distance of the focal spot to the surface of the workpiece is of major interest for the performance of the process, these optical devices are also used to tune the focal length. For example collision danger or dynamic limitations of the handling system may mean that the focal spot has to follow the surface outline without keeping the distance between processing head and material surface constant. Besides cutting and shaping by material removal applications, welding is a kind of application where a focus shift without moving the processing head may be advantageous, especially for 3D processes. Therefore, another deformable mirror is installed near to the focusing optics. Investigations have been carried out on the location of the deformable mirror close to the laser source (RS 3000 RF), and inside the processing head.

Investigations have been carried out comparing thermal cutting using Nd:YAG and CO₂ lasers. Analysis of the investigation results have led to conclusions concerning process efficiency, as referring to better absorption of laser radiation on metal-based materials at shorter wavelength behavior, as well as the influence of using an optical fiber for beam delivery on the processing results. The transmission properties of silica fibers with graded index and step index profile were investigated, when using a high power Nd:YAG laser. The beam parameters behind the two different fiber types related to the input parameters and the fiber geometry were theoretically and experimentally analyzed. The advantages and disadvantages for laser cutting with these fiber types are discussed with respect to physical properties and applicability.

We present a global analysis of the welding process (plasma, keyhole, thermal coupling...). Experimental energy balances of the process are presented and interpreted for different welding conditions. Then a modelization of the keyhole and of the power deposition inside it allows us to quantify the absorption process inside the keyhole (plasma absorption by Inverse Bremsstrahlung effect and Fresnel absorption). The explanations of our experimental results can then be confirmed. The influence of the welding speed on the keyhole geometry is pointed out, and the consequences on the absorption process are explained.

A process variant for laser beam welding of aluminum alloys using high-power CO₂- and Nd:YAG-lasers is presented. In this variant, the advantages of the cw- and the pulsed laser welding are combined by modulation of the laser beam. For quite a lot of Al-alloys fairly good welding results are achieved on the butt and overlap joint. The weldability ranges become larger and it is possible to weld with lower mean powers than in the cw-operation.

High power solid state lasers are increasingly being used for drilling and cutting of advanced materials. This is because of the difficulty in machining, in particular, drilling of small diameter holes, using conventional methods. The pulsed Nd YAG laser is an excellent tool for fine drilling and cutting of these materials because of its combination of high peak power pulse capability and its low beam divergence. A program of experimental work has therefore been carried out to examine the practical effects of key laser variables on the drilling of the Ceramic Matrix Composite material. The parameters used and the systematic approach to the trials is also presented along with information on how statistically significant and repeatable results were obtained.

Due to the good performance shown by laser welded joints, to the quality and repeatability achievable by this welding technique and to its high process productivity, a feature inherent to the laser technology which, together with its high flexibility, allows different operations to be performed by a single source, consistent savings in a production line may be obtained. Therefore laser welding techniques may be of high relevance for industrial applications, provided that a sufficient attention is paid to avoiding a low utilization time to the operating laser source. The paper describes a feasibility study for the integration of a laser source as an automatic unit for circumferential butt welding of tubes in production lines of pipe coils, just before the cold bending station. Using a 6 kW CO₂ source, thickness ranging from 3.5 to 11.2 mm in carbon, low alloyed Cr-Mo and austenitic stainless steels, have been successfully welded. Cr-Mo steels require on line preheating treatment, which however can be achieved by laser defocused passes just before welding. The results of the preliminary qualification performed on laser welded joints of the involved topologies of product (materials, diameters and thicknesses) are described together with technological tests required for approval: laser circumferential butt welding of tubes has proven to be effective, with satisfactory and repeatable results and good joint performances. An exhaustive comparison with current welding techniques (TIG, MIG) is then carried out, along with a detailed analysis of the potential advantages and benefits which may be expected by using the laser welding technique, as well as with a first estimation of the investments and running costs. Since laser productivity is saturated only at a rough 35% during the year, an accurate analysis of other possible applications and of a possible lay out of a laser working cell integrated in the factory production lines is performed. Usually little attention is given to this problem and this is one of the causes of uncertainty when investments in a laser are planned. In most cases a source is devoted to a single application, even if effective working time is really low due to laser fast processing. Therefore potential benefits are substantially reduced to a minimum amount of what can be expected by this flexible technology.

The spatial and temporal beam characteristics of 5 kW power CW pumped CO₂ laser with controllable mirror in the cavity have been investigated. The five-pass unstable cavity with M equals 2 magnification was used, where one of the folding mirrors was replaced by a water cooled flexible mirror based on bimorph piezoelement. The pulse-periodical regime of laser generation in broad frequency range of controlling signals with the 100% beam power modulation depth was realized. The maximal pulse power value exceeding three times the average power level was obtained at 3.8 kHz pulse repetition frequency.

This paper discusses the principals of automatic laser beam positioning, and shows that two distinct advantages are achieved over using a conventional fixed mirror system: (1) The initial alignment of the system may be achieved significantly faster than when using conventional techniques, making multiple workstations for one laser more economic. (2) The laser beam may be maintained during processing, and hence the optimum process parameters maintained through the process cycle. The system was developed as part of a 50 m long beam path operating over power ranges from a few hundred watts to 6 kW. Results are given showing the `beam wander' of a laser system as the laser is run through heating and cooling cycles, hence showing the necessity of in process alignment at this location. These results are then compared to results obtained during closed loop position control. The design of the beam position sensor is based around the use of a silicon leaky mirror customized to have a low value of transmitted power, and reflectivity greater than 99.8%. The transmitted radiation is then focused down onto either a one or two quadrant thermopile detector system, depending upon the length of the beam path, and the desired positional accuracy. This motorized system is then used as part of a closed loop control system and the performance of the system evaluated. Results for positional accuracy and response rate are given, and the system shown to have a high degree of accuracy, coupled to a relatively fast response rate at a low capital cost.

A delivery system for high-power laser beam (HPLB), with the total optical path 51 meters long, was reported in this paper. The HPLB was delivered through different ambience-copper protecting pipes, indoor and outdoor atmosphere while being propagated by the system. The transmissive efficiency of the system was measured while the laser beam power varying from 0.85 to 2.00 kilowatts. The far-field intensity distribution of the HPLB at 55 meters from the laser device after delivered by the system was studied theoretically and experimentally.

Joint arrangements at the automobile-body can show wide gaps and joints due to the tolerances in the sheet part production. If those joint arrangements lie in the later visible area or are prepared if a joint for repair work is needed, they are nowadays joined by brazing. Brazing offers, through the filler metal amount, a moulding material which can be finished more easily than comparable weld seams. Through the brazing of sheet parts, repair work can be carried out in an easier way than it would be the case with welded joints. Still, manual brazing, especially manual flame brazing, involves some problems regarding the fluctuating brazing quality and the great heat input together with the resulting thermal damage of the basic material and the filler metal. The application of the Nd: YAG-laser as a brazing tool presents itself for the following reasons: - good control as a prerequisite for a process control - strictly and locally limited heat input and the defined setup of temperature fields as a result - laser beam guiding via optical fibres as a reason for the high capability of integration into the production systems

During cutting certain materials like aluminum by using CO₂ laser, slag is generated and attached to the lower edge of the cut kerf. This slag is generally not accepted and is difficult to remove. This paper describes the results of an experimental program to prevent the slag attachment by painting the rear surface of the work piece with a thin layer of aluminum oxyacetylene welding flux. Results shows that perfectly slag-free cut can be obtained by this method.

Applications of high power lasers in material processing can be divided into surface treatment, welding and cutting. An overview of the main physical mechanisms underlying these applications shall give a systematic basis for modeling the processes. The absorption behavior of a CO₂-laser beam is discussed, mathematical attempts for describing the heat conduction are compared and a distinction between the several appearing melt flow phenomena is made. Further treated effects are evaporation, plasma formation and time dependence. Models of hardening, deep welding and cutting are presented to give examples for the mathematical treatment and the predictions and analysis that can be done.

A qualitative analysis of the role of some hydrodynamic flows and instabilities by the process of laser beam-metal sample deep penetration interaction is presented. The forces of vapor pressure, melt surface tension and thermocapillary forces can determined a number of oscillatory and nonstationary phenomena in keyhole and weld pool. Dynamics of keyhole formation in metal plates has been studied under laser beam pulse effect ((lambda) equals 1.06 micrometers ). Velocities of the keyhole bottom motion have been determined at 0.5 X 10⁵ - 10⁶ W/cm² laser power densities. Oscillatory regime of plate break- down has been found out. Small-dimensional structures with d-(lambda) period was found on the frozen cavity walls, which, in our opinion, can contribute significantly to laser beam absorption. A new form of periodic structure on the frozen pattern being a helix-shaped modulation of the keyhole walls and bottom relief has been revealed. Temperature oscillations related to capillary oscillations in the melt layer were discovered in the cavity. Interaction of the CW CO₂ laser beam and the matter by beam penetration into a moving metal sample has been studied. The pulsed and thermodynamic parameters of the surface plasma were investigated by optical and spectroscopic methods. The frequencies of plasma jets pulsations (in 10 - 10⁵ Hz range) are related to possible melt surface instabilities of the keyhole.

Various mathematical models have been developed at the R.T.M Institute with the aim of producing an instrument for understanding the phenomena of heat transmission by conduction in material subject to a laser radiation. In this paper we consider monodimensional, bidimensional and tridimensional models; they are able of describing the thermal field versus time and depth. To obtain the equation which gives the temperature pattern at various depths and as a function of time, some simplifying hypotheses were made. Normalization was then carried out in order to identify the parameters with physical meaning and to bring the equation into a more general use. Following the development phase of the mathematical models, the models have been checked with experimental tests on some ferrous alloys. The behavior and resultant metallurgical structure in common steels when subject to low and high thermal gradients from laser radiation were evaluated. The correspondence of the models to the experimental values indicates that several simplifying hypotheses made in developing the models do not invalidate them. Moreover it can be state that the possible errors arising from their use create effects which are self-compensating. A comparison of the mentioned models has also been carried out and their field of validity has been studied.

In designing classical controllers it is necessary to assume that the parameters of the system are reasonably well known. However the ablation process involves inherent nonlinearities and significant uncertainties in the model parameters, which are one of the main problems for designing an appropriate controller. Nonlinearities occur e.g. due to the chemical processes or due to the changing the absorption or the gas flow. The concentration of added oxygen to the assisting gas stream influences the system behavior significantly. It will be shown that the nonlinearities depend on the process parameters. A simplified nonlinear process model based on an analytical investigation is presented and discussed. To get a glimpse of the time constants, nonstationary investigations are carried out. The best way to control such a complex nonlinear system is to use an input-output map. This can be settled with an experimental off- loop identification or by fuzzy inference. A fuzzy controller itself has a nonlinear behavior and allows designing an appropriate controller without any mathematical model of the process.

During welding of sheet metals with high performance CO2-lasers various unsteady processes occur which are disturbing the performance capabilities ofthe workpiece. Figure 1 gives a schematic overview on different kinds of these transient processes. They take place at the beginning (pos. 1) and the end of the process (pos. 4) as well as at critical workpiece contours (pos. 3). This kind of l;ransient processes can be predicted and therefore it is possible to take them into consideration while plaiiniiig the machining. But also during quasi steady periods (pos. 2) of the welding transient processes occur, that are caused e.g. by changes in the surface finish or by fluctuations of the laser output OWCF or only by the coupling of nonlinear effects. The latter kind of transient processes cannot be predicted. Therefore a highly precise local machining quality can only be achieved, if the transient process is well understood and controlled. Detector systems are required to get a deeper knowledge of the process. To influence the processing results a modular control system has been developed

The use of high power CO₂ lasers in welding enables processing with high laser intensities at the workpiece which is connected with the formation of a laser induced plasma at the surface of the workpiece. Therefore the effect of deep penetration welding by formation of a plasma filled keyhole and plasma plume above the workpiece is possible, including the risk of plasma shielding, which means strong absorption of the incident laser beam above the workpiece and thus interruption of the welding process. The conditions for ignition of plasma shielding, which is determined by electron density, are mainly influenced by laser intensity, process gas and material. Variations of these parameters have been conducted in order to find limits for the appearance of plasma shielding. Experimental data are used to verify a model concerning the absorption mechanism of a stationary shielding plasma state. The dynamic behavior is treated by time resolved spectroscopic analysis of the light emitted by the plasma above the workpiece yielding monitoring signals that have a strong correlation with the formation of plasma shielding. Based on these investigations a closed-loop process control in continuous high power laser welding has been developed. Using the intensity of a spectral line of laser induced plasma as monitoring signal and the regulation of laser intensity via laser power, plasma shielding can be suppressed. From the industrial point of view increase in economy and reliability of the laser welding process combined with quality improvements which are induced by the application of the plasma shielding controller (PSC) are of great importance. For this reason three examples of PSC application are presented.

In order to control CO₂ laser treatments, a precise knowledge of the CO₂ radiation- surface coupling is required. For this purpose, numerical identifications of the absorption coefficient, either with temporal resolution in non stationary 1D configuration or with spatial resolution in a stationary 2D configuration, were achieved from thermal cycles measurements and simulations. Evolutions of the coupling during laser treatment were studied both in the case of coated steel hardening (graphite and manganese phosphate coatings) and in the case of solid state nitridation of titanium alloys. Moreover, the determination of the CO₂-surface coupling for those thermodiffusional solid state laser processes had been used to correlate experimental treated depths to those obtained by a simple thermodiffusional model taking into account carbon or nitrogen diffusion under a calculated thermal cycle.

This article deals with on-line control of laser melting including laser beam control. A control induces some advantages which are an improved quality of the treatment and more regular results, with the object to industrialize the process. The studied application is laser remelting of cast iron. The laser is a UTIL CW CO₂ of 22 kW maximum power. The process which is developed to improve proprieties is described, the physical process is modelled and the experimental setup is depicted. The commands (mainly: sample velocity, laser power and intensity distribution) and the outputs (molten depth) are chosen in accordance with the application under consideration. Internal closed loop control is formulated and used to regulate incident laser power. Different sensors have been experimented such as C.C.D. camera. Disturbances in the molten zone have been experimentally observed. The average molten depth has been considered as the first output to regulate. It is estimated from molten pool dimensions measured by the CCD camera and image on-line processing. This process is modelled from two command variables, then internal parameters are identified and finally the molten depth control on-line could be obtained.

On the basis of previous work, the development of a model-based monitoring and on-line automatic regulation system applicable to the real-time control of laser welding and surface heat treatment has been undertaken. In both kinds of applications, the main diagnosis system considered in the control loop is a thermal camera either used to provide a 2D temperature map or, more suitably according to typical response time parameters, used as a line scanner sweeping the appropriate diagnosis zone. From the automatic regulation point of view, the developed control system is defined to correct typical perturbations in incoming laser power, material thickness or piece motion speed within the appropriate time scale in order to assure a practical validity of the in-course weld seam or heat treatment track, respectively. The resulting control module, grounded on reasonably reliable calculations of the processes parameters performed with own-generated models provides a valuable tool for the practical implementation of the referred applications with special regard to quality assurance purposes.

As more powerful solid state laser sources appear on the market, new applications become technically possible and important from the economical point of view. For every process a preliminary optimization phase is necessary. The main parameters, used for a welding application by a high power Nd-YAG laser, are: pulse energy, pulse width, repetition rate and process duration or speed. In this paper an experimental methodology, for the development of an electrooptical laser spot welding monitoring system, is presented. The electromagnetic emission from the molten pool was observed and measured with appropriate sensors. The statistical method `Parameter Design' was used to obtain an accurate analysis of the process parameter that influence process results. A laser station with a solid state laser coupled to an optical fiber (1 mm in diameter) was utilized for the welding tests. The main material used for the experimental plan was zinc coated steel sheet 0.8 mm thick. This material and the related spot welding technique are extensively used in the automotive industry, therefore, the introduction of laser technology in production line will improve the quality of the final product. A correlation, between sensor signals and `through or not through' welds, was assessed. The investigation has furthermore shown the necessity, for the modern laser production systems, to use multisensor heads for process monitoring or control with more advanced signal elaboration procedures.

The here presented monitoring method is based on the UV-light detection being emitted by the welding plasma plume and the measurement of the near-IR radiation of the glowing spatters which are thrown out of the welding pool. The results of the above mentioned spatter detection are used to approximate the size of the occurred holes in the weld. A third sensor is used for monitoring the workpiece temperature. This additional signal is very important when welding thin metal sheets (e.g. overlap welds). Further the implementation of the presented monitoring method in an industrial instrument is described. This instrument is a self-learning real-time monitoring system which needs several teach welds for creating a position-true reference. In the following automatic mode it compares the most important features of the actual weld with those of the learned reference. Using fuzzy-logic routines the probability is determined that a metallographically important welding failure has happened. The LWM 900 has been developed initially for monitoring the CO₂-welding process. The Nd-YAG laser welding process differs slightly from it. This fact has to be considered accordingly for a proper signal detection. Additionally, due to the fact that most of the used detectors are sensitive to the wavelength of the Nd-YAG laser, some measures have to be considered to reject unwanted influences in this connection.

Recent studies and tests have shed light on the large role played by fluid-dynamics phenomena on laser processing. They are responsible for the largest portion of the losses in the welding and cutting processes. The mechanism by which these losses occur is here explained and their values are given. Assist gas system improper design and use cause strong flow field instabilities and worsened chokings that impede the assist gas primary function of removing, by fluid-mechanical action, the molten material from the cut slit, and in the case of an exothermic reacting gas also the other essential function of sustaining even a slow stoichiometric burning. Flow visualization and phenomenological analyses have given a better insight on the involved phenomena and suggested new nozzle designs for laser cutting.

CO₂ lasers are increasingly being utilized for quality welding in production. Considering the high equipment cost and high productivity, the start-up time and set-up time for new products should be minimized. Today most parameters involved in laser welding still have to be manually fine-adjusted when initiating welding of a new product. Ideally the parameters should be set and optimized more or less automatically. In this work the feasibility to automatically optimize the focal point position, one of the most critical parameters in laser welding, is analyzed. In a number of systematic laboratory experiments, a 1150 W CO₂ laser is used to weld 2 mm sheets of mild steel. In the experiments the focus point position is continuously changed during a welding trial, and the process is simultaneously monitored by two photo diodes, one on either side of the workpiece surface. In a number of systematic investigations, the welding speed and the power level are varied. After welding, a number of artificial neural networks are designed to recognize the optimum focus point position. The efficiency and accuracy of the neural networks are then tested on new welds, performed with similar parameter settings as the first set of welds performed. The results show good agreement between the real position of the optimum focus point and the calculated values. Finally a trained neural network has been implemented into a closed-loop control system with one top side photo diode as a sensor. Preliminary test demonstrate that neural networks can be used to optimize the focus point position with good accuracy in cw CO₂ laser welding.

In laser beam welding a variety of complex physical interactions take place, leading to a fluctuating process behavior. Most of the available in-process control facilities measure signals emitted from the interaction zone like the light-emission in different spectral regions or acoustic waves. The obtained signals contain statistic as well as periodic components, from which information about the temporal progress of the process has to be derived by well adapted signal analyzing methods. The paper is presenting a `hardware'-tool for process diagnostics in laser beam welding that has been developed. By several examples the application of different signal analyzing techniques is explained considering the signal level, signal statistics and frequency analysis. Finally, advantages and disadvantages are discussed in context to industrial use.

The growing significance of laser technology in industrial manufacturing is also observed in case of plastic industry. Laser cutting and marking are established processes. Laser beam welding is successfully practiced in processes like joining foils or winding reinforced prepregs. Laser radiation and its significant advantages of contactless and local heating could even be an alternative to conventional welding processes using heating elements, vibration or ultrasonic waves as energy sources. Developments in the field of laser diodes increase the interest in laser technology for material processing because in the near future they will represent an inexpensive energy source.

This paper includes a theoretical description of some of the major physical phenomena of thermal cutting processes in general. The work is mainly focussed on the laser cutting process. Qualitatively and some quantitatively descriptions of the melt front propagation and the melt flow is described. The theory, supported by experimental studies shows, that in high quality thermal cutting, the melt flow is in front of the cut kerf with a uniform pressure at the melt surface. Furthermore is shown, that at high cutting rates, evaporation in the lower central part of the cut kerf forces the melt partially around the laser beam, reducing the cut quality. Theoretical estimation of the melt film thickness in thermal cutting is derived. It is shown that there is a maximum cutting speed, where substantial evaporation in the cut front can be neglected. This maximum cutting speed depends upon the thermal properties of the material, the thickness of the material and the pressure from the cutting gas. Furthermore the paper indicates thermal instabilities in the top of the cut front in thermal cutting processes, which is supposed to be responsible for the striation formation.

For laser beam cutting of contour elements, the influence of the contour geometry has been examined due to a local and time-dependent preheating of the material. The paper presents a simulation of the temperature field in workpieces with different cutting contours calculated by the finite element method. By measuring the light emission from the cutting front and the molten material, the dynamical behavior of the cutting process can be characterized. The comparison of the local temperature at the time the laser beam passes and the obtained process signals with the resulting cut quality reveals the influence of preheating on the striation formation, on local cut surface defects, and on clinging dross. The simulation can help to detect critical contour elements for a given material and parameters set and to optimize the process parameters for a given contour.

A comparison of TIG welding and laser welding of INCOLOY 800 is presented under two different aspects: weld pool sensitivity to minor elements and modelling of stresses and temperatures distribution. For TIG welding, welding parameters have to be adjusted when changing of INCOLOY 800 master melt. It appeared that laser welding did not depend on the material chemistry and gave a good reproducibility of the results, whatever is the mater melt, with the same parameters. Thermal modelling was developed for a tube-tubesheet configuration. TIG modelling showed a stress localization for several chemistries, which indicated a risk of cracking at the root of the weld. The modelling showed how it is related both to the temperature of the base material close to the molten pool, and the duration of the process. For the INCOLOY 800, the longer the temperature is in the 800-1000 degree(s)C range, the higher the risk of cracking exists. For laser welding, the risk is much lower, because the process is incomparably faster.

We investigate the propagation of a high power CO₂ laser beam through a powder stream in the condition of laser surface cladding. During this process, a powder material and a gas are blown coaxially with the laser beam, toward a laser generated melt layer on a moving substrate. The final result in terms of surface properties, depends on a number of parameters including laser beam intensity, powder nature, flow rate and distribution, nature and velocity of the gas mixture in the interaction volume, The influence of the various parameters have been investigated experimentally and an evaluation of the laser energy redistribution in the interaction volume above the solid sample has been made. Calculations show the range of variation for the main directly adjustable parameters: dynamic action of the transport gas and laser beam intensity. A classification of the relevant parameters is attempted.

It was demonstrated by the simulation of laser beam annealing process that one can make a great local change in concentration of impurities or intrinsic defects in a Hg_1-xCd_xTe crystals by long (moreover only by such) pulses of laser radiation. The diffusion processes of defects in semiconductors in the presence of high power laser beam can be described using Schottky's thermodiffusion theory. The results of calculations of time- spatial distribution of the concentration of interstitial mercury for pulse lengths 8 ns, 100 ns, and 250 microsecond(s) are presented. These computer simulated results are compared with distribution of Hg concentration in specimens subjected to laser annealing under the same condition.

In the laser cutting process the gas flow is of main importance to remove molten material from the cut kerf. Changes in nozzle geometry, gas supply pressure and nozzle workpiece stand-off distance have a strong influence on the cut quality. The aim of the investigation is the numerical simulation of supersonic gas flow. Supersonic nozzles for laser applications are designed which can be manufactured more easily and cost effective than conventionally used Laval nozzles. For the simulation wall friction is regarded and the flow field is calculated two dimensional and assumed turbulent. Normal jet impingement for the designed nozzles and underexpanded conic-cylindrical nozzles is compared at various nozzle stand-off distances and shows a more constant pressure on the workpiece for the designed nozzles. Furthermore supersonic effects in the cut kerf are investigated and compared with results from Schlieren photographs. The nonlinear pressure distribution inside the kerf indicates both the shock formation and detachment of the gas flow. In the presence of shock waves the existing equations in finite volume form have been modified, as they lead to wrong predictions both in the shock location and strength due to an incorrect inertia term in the momentum equations.

The computer package is presented for modelling of laser influence on the surface in wide range of laser radiation parameters and materials properties. The more extending application of this code is the calculation of 2D thermal field in multilayer structures under the action of moving laser beam. The materials (metals, semiconductors and dielectrics) with different heat conducting properties can be applied for modelling of the structures. The code works well on the curve surface of the structures (deposits or holes). The fundamental dynamics and kinetics of several laser processes have been investigated in some details using this code. The photochemical laser-induced etching in a Cl₂ atmosphere has been investigated. The calculations of 2D differential equations for Cl atoms concentrations produced by gas-phase photodissociation and the photoelectrons generated within Si surface were conducted using our package. The reaction probability was obtained for different laser parameters. On its base we could simulate the depth and feature of etched holes. The method of micropatterning has been suggested. A pyrolitic process of deposition of a metal film on the SiO₂ surface has been considered. The temperature profiles inside of W-SiO₂ structures were calculated. It has been shown that the heating of existing metallization layer is the source of warming up of the SiO₂ substrate following the further deposition of metal film. The metallization layer depth have been obtained at pyrolysis of W(CO)₆.

CO₂ laser synthesis of ceramic powders from gas-phase precursors is an ideal method for growing nanosized, pure and nearly mono-dispersed particles. Results on the production and characterization of Si-based ultrafine powders are presented and interpreted. The microstructural properties of nanosized powders are compared with those of conventional ceramic powders. Novel applications are discussed.

The phenomenon of laser supported absorption (LSA) of CO₂ laser radiation is investigated with spatially and temporally resolved plasma spectroscopy in Argon as ambient gas at pressures of 1 - 10⁵ Pa. A TE-CO₂ laser with a gas mixture of CO₂/N₂/He equals 1/4/4 at a total pressure of half an atmosphere is used. The pulselength of the TE- CO₂ laser is about 6 microsecond(s) at a mean power of some 100 kW. LSA-phenomena and material ablation processes are compared with that of a conventional TEA-CO₂ short pulse laser. It could be shown that longer pulses of less mean power make material ablation more efficient if the absorption wave becomes transparent within the pulse time of the laser. Maximum electron density of 2.5 (DOT) 10¹⁷ and a temperature of 3 eV were measured 1.5 microsecond(s) after the beginning of the irradiation for an expanding aluminum plasma into vacuum.

The present work deals with a new nitriding method applied to titanium: the Ti surface nitriding is carried out by direct laser irradiation in the presence of ambient nitrogen. The experimental procedure is performed in a chamber containing N₂ gas, allowing plasma study by emission spectroscopy. Two pulsed laser types are used, a TEA-CO₂ ((lambda) equals 10.6 micrometers ) and a XeCl excimer ((lambda) equals 308 nm) in order to compare the laser- material coupling influence on the layer synthesis process. The laser beam is focused perpendicularly to the Ti samples. Different experimental conditions are achieved to investigate the influence of laser and gas parameters on the process. Using the CO₂ laser, a N₂ plasma is created on the Ti surface. With the XeCl excimer laser, a Ti plasma on the sample appears. After treatment, the surface state of the samples is studied and chemical analysis of the targets are carried out. The TiN synthesis is evidenced. Presence of oxinitride in the compound and native surface oxygen reduction by hydrogen plasma are examined.

Non-equilibrium sintering of ZrO₂ solid electrolyte, a kind of high temperature superionic conductor, was realized using high-power CO₂ laser beam. The theory and technology of non-equilibrium sintering were introduced. The microstructure of the laser sintered specimens were analyzed by SEM and XRD. The conductivity of laser sintered CSZ and MSZ samples were measured, which were the order of 2 X 10^-2(Omega) ^-1CM^-1 at the temperature of 1000 degree(s)C.

Laser cutting of pure aluminum and its alloys causes problems often due to the high reflectivity and the process stability. Experiments with the cutting gases industrial oxygen and industrial nitrogen in pure and alloyed aluminum (Al99,5 and AlMg3) with and without surface treatment have been performed, and they show improvements in the cutting speed and the cut quality using the right combination of parameters. Advanced surface analyzing methods such as Auger-analysis and SEM have been used in order to analyze the cut kerf and improve the process. The cut quality is evaluated according to the German standard DIN 2310 measuring the roughness and the squareness of the cut kerf. Additionally some corrosion test of the cut kerf have been performed, using the Chemical Measurements by Titration and Electrochemical methods. Mechanically cut surfaces have been used as references for the surface and corrosion methods, in order to compare the `new' laser technique and the `old' traditional one.

In the present paper a globular cast iron surface treated by laser beam has been investigated. In evaluation of the results of experiments with cast iron components, it was found that a structure other than the conventional cast iron structure could be obtained as a result of heat treatment with high power density. Methods like light microscopy, scanning electromicroscopy, X-ray diffraction and DTA were used as test methods in the experiments.

Liquid phase nitridation of TA6V by a high power homogenized CO2 laser had been studied depending on the experimental parameters. Nitrided layers thickness and hardness as well as cracks concentrations and wear resistance were taken into account for the evaluation of experimental optimum parameters.

Layers containing different particles of different sizes (TiC: 2,7 micrometers and 31 micrometers mid size; TaC: 15 micrometers mid size) were formed on the surface of 90 MnCrV8 tool steel. A CO₂-gas laser equipment was used to form these layers. The grain contents of the layers were between 35% - 55%. Some of the ready TiC layers were hardened by laser in order to reduce the retained amount. We compared the wear resistance of the layers employing abrasive wheel test. For reference purposes we carried out the test of traditionally hardened, traded TICALLOY II and TICALLOY W materials as well.

The good chemical resistivity of some polymers generally is connected with poor adhesive properties of the material. Because of this it is difficult to adhere, paint or coat them. This makes a pretreatment procedure necessary. Nowadays mechanical, wet-chemical, or plasma treatments of the workpieces are applied. Most of these methods, however, are limited in practice, for example because they require specific treatment conditions. This is the reason why improvement of the existing technologies and look-out for alternative methods are subjects of current research. One relative new way to change the surface properties of polymers is the use of excimer lasers. In the present paper recent results are presented concerning the interaction of UV-laser radiation with polymers. The emphasis here is the photolytical modification and activation of their surface. On the basis of a proper activation, for example, a significant enhancement of the adhesive bond strength between a polymer and an adhesive (in this case epoxy resin on polypropylene foil) has been achieved.

A powerful adhesion of fluororesin (Teflon) featuring its excellent corrosion resistance and stainless steel was performed by using an epoxy resin-based bonding agent. Adhesion strength was 500 times more than that of untreated teflon, which has virtually no affinity with chemicals and solids. The teflon surface was irradiated by an ArF excimer laser light with energy higher than the carbon-fluorine bond, in a tetrahydroborate (BNaH4) and methyl alcohol (CH3OH) mixed solution ambient. The defluorination of the surface was performed with the boron atoms which were photodissociated from BNaH4. The fluorine atoms of the surface was replaced with the CH3 and OH radicals, also photo dissociated from CH3OH. The methyl(-CH3) and hydroxyl(-OH) groups, which have a good affinity with epoxy bonding agent, were substituted only for the area exposed to the laser light. The modified teflon surface was adhered to a stainless steel with the epoxy bonding agent, and shearing tensile strength test was performed. The strength was 100 Kgf/cm2, whereas untreated teflon's strength is 0.2 Kgf/cm2 or less. Thus the adhesion was improved considerably.

A pump and probe laser scheme was devised to obtain time-resolved imaging of plasma formation and shock wave evolution during photoablation of solid targets by a XeCl excimer laser. The analysis of the observed illumination patterns furnished quantitative data on the interaction process.

Laser ablation of layer structures made of optically and thermally dissimilar materials is markedly different from ablation of homogeneous bulk materials. In the case of supported thin films the ablation characteristics are influenced by the variation of the material properties at the interface. This concept is highlighted by comparing experimental and thermal calculation data on pulsed laser ablation of metal, tin oxide and indium-tin oxide films from glass support to those of characterizing bulk ablation.

Production of holes and grooves of < 30 micrometers diameter with high aspect ratio value is a delicate task either for mechanical tools, or for conventional nanosecond pulse lasers like e.g. pulsed Nd:YAG or excimer lasers. They later tend to cause microcracks extending from an annular melting zone, or substantial disruption, respectively. Experimental results are presented which demonstrate that the development of intense ultrashort pulse laser systems (>> 10¹² W cm^-2, (tau) < 1 ps) opens up possibilities for materials processing by cold plasma generation and ablation of metals, semiconductors, ceramics, composites, and biological materials. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs (< 200 (mu) J) and 7 ns (< 10 mJ), and center wavelengths at 612 and 600 nm, respectively, both focused on an area of the order of 10^-5 cm², have been applied either to absorbing substrates, like polycrystalline gold, silicon (111), aluminum nitride ceramics, or transparent materials, like synthetic and human dental hydroxyapatite composites, bone material, and human cornea transplants. The fs-laser generates its own absorption in transparent materials by a multiphoton absorption process, and thus forces the absorption of visible radiation. Because the time is too short (< ps) for significant transport of mass and energy, the beam interaction generally results in the formation of a thin plasma layer of approximately solid state density. Only after the end of the subpicosecond laser pulse, it expands rapidly away from the surface without any light absorption and further plasma heating. Therefore, energy transfer (heat and impulse) to the target material, and thermal and mechanical disruption are minimized. In contrast to heat- affected zones (HAZ's) generated by conventional nanosecond pulse lasers of the order of 1 - 10 micrometers , HAZ's of less than 0.02 micrometers were observed.

Excimer laser surface processing is well-known for material ablation, cleaning, deoxidation, smoothing or roughening. A typical industrial application is the polymer ablation for electronic components, however, the treatment of metals is only on the threshold of industrial use. A novel application reported here, may be an excimer treatment in air leading to oxide and nitrogen dissolution, resulting in an improved corrosion resistance. It is known from literature that corrosion resistance can be enhanced by laser surface alloying e.g. gas nitriding of Ti using CO₂-lasers. However, all these techniques have the disadvantage of producing inhomogeneous layers. The aim of this study was to use the reactions during excimer laser irradiation of steel in air to produce layers in the thickness range of 0,1 to 2 micrometers with novel properties. Using the Siemens XP2020 excimer laser it was possible to scan technologically reasonable surface areas with energy densities in the range of 20 to 80 mJ/mm² and several pulses per area. Steel sheets of 1.4541 (DIN) were irradiated in air and subsequently analyzed by XRD, SEM, TEM, AES and Mossbauer spectroscopy. The corrosion behavior was tested potentio-dynamically in 0,5 N H₂SO₄ and by gravimetric measurements of the weight loss. The XRD results showed, that the remaining delta-ferrite was eliminated. Both Mossbauer and Auger spectroscopy indicated a strong N- dissolution, hereby stabilizing the austenite. The TEM-investigations revealed fine dispersed oxides (chromites) and an increased dislocation density, resulting in pre-cellular arrangements after relaxation. Corrosion tests suggested the reduction of the material removal rates by a factor of 10 compared to untreated samples. The U(i) curves showed that after the excimer treatment less Cr is presented due to oxide formation in the surface layer. These Cr-oxides are the main reason for the improved corrosion resistance of excimer laser treated stainless steel.

Aluminum alloys typically have as received reflectivities of 85 - 95% at 10.6 micrometers making many laser processes difficult or impossible. These values have been reduced to as low as 1 - 2% by optimizing the processing parameters of an excimer laser used to modify the surface structure of 8090 and 2024 Al alloys and pure Al prior to their exposure to a CO₂ laser. The most significant excimer processing parameters were found to be the scan pattern of the excimer beam, the number of pulses per scan pattern step (dwell time) and the laser fluence. Optimizing these parameters allows the production of a rough oxide rich surface and reflectivities at 10.6 micrometers routinely below 10%. Preliminary results are presented from the practical implementation of the technique to a dual wavelength (CO₂/excimer) cutting system. Increases in cutting speeds of between 2 - 4 times are demonstrated with 8090 Al-Li alloy using dual wavelength laser processing.

Laser-induced wet chemical etching of Co, Cr, Cu and Ti in aqueous solutions of potassium hydroxide and phosphoric acid was investigated using an Ar-laser operating at 514 nm. Etching of thin metal films on glass substrates and metal foils was obtained at static etch rates up to about 10 micrometers /s at an incident laser power of about 1 W. Measured background etch rates were less than 10^-5 nm/s. EDX-analysis of Ti foils etched in phosphoric acid revealed no enrichment of phosphorous near the laser interaction zone. An observed exponential dependence of static etch rates on laser power is interpreted in terms of dominating thermally activated chemical reactions at the metal surface. Laser direct writing of thin transparent lines in metal films on glass was obtained at writing velocities of about 1 mm/s and a laser power of about 0.3 W. Smallest line widths of about 3 micrometers were obtained which are about a factor of two smaller than the laser focal spot diameter. This observation is in agreement with dominating thermally activated surface reactions. Cutting of thin Ti foils (25 micrometers ) was obtained by laser chemical etching at a velocity of about 30 micrometers /s and an incident laser power of about 0.8 W. Wall angles between 70 and 80 degree(s) were found to depend on experimental parameters.

Irradiation of sintered Al₂O₃ plates has been performed using an excimer laser ((lambda) equals 248 nm) and the resulting structural transformation occurring at and near the surface of the plates has been characterized. Low-angle X-ray diffraction reveals a sequence of surface structural modifications which are correlated with the actual energy injection into the material (laser fluence and number of pulses) and the occurrence of very large energy gradient between surface and bulk. At low fluence, surface roughness is increased without any evolution of the initial (alpha) -alumina phase of the materia. Increasing the laser power density results in (gamma) -alumina formation near and at the surface of the plates.

In this paper, the preparation of SiGe films grown onto amorphous or single crystal substrates by pulsed excimer laser crystallization of heavily Ge implanted silicon is proposed as an alternative to classical MBE and CVD techniques. Processed films were characterized by ions (channeling-RBS) and optical (Raman) techniques.

Due to their unique physical properties (high thermal conductivity, high electrical resistivity) aluminum nitride (AlN) ceramics are attractive materials for applications in electronics and other medium or high power electrical networking. In this contribution, the change of surface configuration of sintered AlN plates is studied as a function of excimer laser irradiation conditions (fluence, number of pulses). Before irradiation, Auger Electron Spectroscopy reveals a surface composition which is characteristic of the AlN synthesis process, i.e. N, O and C atoms are present, without any evidence for Al. At high laser fluences, irreversible decomposition of AlN takes place, producing free Al atoms at the surface. At low fluence, long-term and reversible modifications are detected, leading to the formation of metastable nitrogen oxides. The kinetics of these laser-induced reversible modifications is analyzed and a model is proposed to support these experimental evidences and to explain the AlN permanent decomposition.

There is a variety of techniques which can be used in the fabrication of diffractive elements. However, none of them is completely satisfactory due to lack of resolution, high costs or duration of process. On the other hand, high power excimer lasers have been shown to be effective in micromachining of surfaces with high accuracy. In the following we discuss the possible use of excimer laser beam to fabricate diffractive elements. We show that a resolution, high enough to diffract light with high efficiency in the visible is not possible. For longer wavelengths, specially the widely used 10.6 micrometers of CO2 lasers, the grooves that can be made, are satisfactory in the case of materials like Zinc Selenide or Zinc Sulfide used for making lenses and coatings but not in the case of reflective materials like Copper and Molybdenum.

The pulsed laser deposition is now routinely used for the growth of a variety of oxide materials in thin film form. Superconducting, ferroelectric, magnetic or biocompatible oxide films are easily grown in this way. Epitaxial films, multilayers or superlattices based on various oxide materials have been also realized using this deposition method. The quality of the oxide films grown by the pulsed laser deposition technique depends upon the various phenomena which occur during their formation. Thus, we discuss in this paper the influence of the precise growth conditions on the atomic composition, surface morphology, structural and chemical nature of the pulsed laser deposited films. A special attention has been paid to the problem of the epitaxial growth of BiSrCaCuO and BaTiO₃ films on MgO single crystal substrates.

Copper for electrotechnical applications and tin bronzes, which are used in mechanical engineering, were chosen for alloying, respectively remelting experiments. The surface treatment was carried out on ground samples which have not been coated for better absorption. A pulsed 450 W Nd:YAG laser with rectangular beam profile was used. The alloying operation has been performed either as a one step process or in remelting preplaced filter materials. Investigations about the formed microstructure and the resulting hardness have been carried out. The possibility to alloy copper surfaces to higher depths, and the influence of different alloying elements are discussed.

In this study, we have prepared BN thin films deposited on a silicon substrate using the laser ablation technique. The irradiation of boron nitride target by a NdYAG laser (with two wavelengths: 532 and 266 nm) and by an excimer laser (193 and 248 nm) leads to films which are characterized by Fourier Transform Infra-Red spectroscopy, and mainly by X-ray Photoelectron spectroscopy (XPS) and laser microprobe coupled with mass spectrometry (LAMMA). In a first step, we have investigated the laser-target interactions by XPS spectroscopy and LAMMA microprobe, in this last case, we compare the spectra both in positive and negative modes obtained by analysis of the different films (realized by laser ablation deposition at 266 nm) with those of reference materials: BN (target used for the films synthesis) and B₂O₃ (oxide which could be formed in laser ablation experiment). The results underline the role of the oxygen traces in the synthesis vacuum chamber leading to a film in which oxygen is inserted in the boron nitride lattice but not under the B₂O₃ structure. On the other hand, the XPS analysis of the films realized at 532 and 266 nm show that the boron is found in two different states: the first one corresponds to the boron bound to nitrogen (BN) and the second one is attributed to the elementary boron with oxidation state zero. All the analysis performed on the films prompt us to conclude that elementary boron detected by XPS experiments is formed during laser ablation leading to nitrogen deficient films. Finally, we show that the laser ablation of the boron nitride target with the 248 nm laser wavelength allows to obtain a thin film in which the boron is detected in only one state of binding (boron bound to nitrogen) by XPS spectroscopy. The profitable effect of the 248 nm laser irradiation on the stoichiometry of the obtained BN film could be due to the Band-Gap absorption phenomena.

Ductile iron in as-machined surface was remelted by a high power pulsed Nd:YAG laser. Processing efficiency, microstructure and hardness of the laser remelted layers were investigated as a function of processing parameters. Microstructural changes after successive multi-pass overlap remelting were studied. It is demonstrated that the processing results were sensitive to pulse frequency, pulse power density and spot diameter, while surface conditions have only minor influence. Depending on processing conditions, two types of microstructures in the laser remelted zone were observed. An extremely fine dendrite-free lamellar eutectic structure occurred in the surface layer of the melted track. In the lower part of the remelted track, a plate-like ledeburite interspersed by small amount of primary austenitic dendrite was present. In overlapping tracks, the previous rapidly solidified ledeburite was ultra-rapidly graphitized by the heat input from the successive remelting track. The thickness of the graphitization zone and the graphitized microstructure were closely related to the processing conditions. The phenomenon of the rapid graphitization has not been reported so far and is discussed as a consequence of the cycling temperature fluctuations during pulsed laser heating. The results were finally compared with those obtained with a CO₂ laser using cw- radiation.

Solid-liquid phase transitions initiated by nanosecond heating of Si surface with monopulse radiation of a ruby laser have been studied. Changes in the aggregative state of Si were diagnosed by optical probing of irradiated zone at 0.53 or 1.06 micrometers and by means of thermal radiation pyrometry at the effective wavelength of 525 nm. Dynamics of the probing radiation reflection and scattering were studied by directing the probe beam at the central region of the irradiated zone both directly and from the backside through the specimen volume. Numerical modelling has been conducted of the phase transitions and optical absorption at (lambda) equals 1.06 micrometers under the internal reflection of probing radiation from moving liquid-solid interface. It has been shown that the surface temperature of the melt is nearly constant at the epitaxial crystallization stage. At the onset of melting and at the end of solidification stage, the Si surface is optically nonuniform due to coexistence of crystal and liquid microscale areas. The typical size of heterogeneous surface irregularity has been estimated. Local fluctuations at the moving liquid-solid interface result in irregularity of the liquid-solid interface that causes scattering of the probe radiation. Possibility has been demonstrated of using optical diagnostics of phase transitions occurring under laser irradiation of a semiconductor immersed in translucent liquid (water), where traditional optical probing is not effective.

We have investigated the velocity distribution functions of atoms in laser produced plasma. In our experiments plasma is cheated during the laser sputtering of YBa₂Cu₃O_7-x ceramics target. We used KrF excimer laser for target sputtering. All sputtering conditions that were the same as usual for high T_c films deposition are used. We used time-of-flight method to investigate the velocity distribution function. To measure the instantaneous significance of particles' density we used the laser induced fluorescence technique. We investigated the velocity distribution of Y atoms. These measurements were made at different distances from the target L (5, 10, 20, 30, 45, and 95 mm), at different significance of laser radiation energy fluence (Phi) (0.5 and 3 J/cm²) and at different pressure of buffer gas (10^-4, 10^-2, and 0.15 Torr). These experiments have showed that velocity distribution function depends upon the energy fluence (Phi) . At low (Phi) equals 0.5 J/cm² we didn't observe the atoms with velocity more than 10 km/s at any L. The acceleration of atoms was detected. The velocity corresponding to the maximum of distribution function changed from v equals 2 km/s at L equals 5 mm up to 6 km/s at L equals 30 mm. There were not any changes in distribution function at L > 30 mm. At high (Phi) equals 3 J/cm² one can distinguish two groups of atoms. The first group with low velocity (v equals 2 - 5 km/s) has approximately the same behavior as have atoms at (Phi) equals 0.5 J/cm². The second group of atoms experiences a strong acceleration during the plasma expansion. Their velocities change from 5 km/s at L equals 5 mm up to 25 km/s at L equals 45 mm. The stabilization of the distribution function shape takes place at L equals 45 mm. This result is in contradiction with the gas dynamic model. We have decided that these atoms arise due to recombination during plasma expansion. The ions experience the acceleration in own plasma electrical fields before recombination. This is the main reason of high energy atoms appearance. The buffer gas influences on the high velocity atoms above all. At the pressure p equals 10^-2 Torr the amount of low velocity atoms is approximately the same as at p equals 10^-4 Torr, but the amount of high velocity atoms at p equals 10^-2 Torr is 100 times less than at p equals 10^-4 Torr. This result also can be easily explained if we suppose that high velocity atoms arise due to recombination process.

The GaAs thin films were obtained by laser ablation technique. GaAs target and KrF excimer laser radiation ((lambda) equals 248 nm, E equals 0.3 J) were used. We excluded the drops, generated during the target sputtering, due to using special equipment. The deposition temperature was varied from 150 up to 450 degree(s)C. The x-ray analysis have showed that films have a monocrystalline structure at some temperatures. The interface thickness was tested by Auger method. These measurements showed that interface thickness is less than 5 nm. Using this laser ablation technique we have produced the p-n junction.

The interaction of CO₂ laser radiation with mixtures of silane and molybdenum hexacarbonyl (vapor) results in solid Si/C/O/Mo material and various gaseous compounds (mainly CO). The XPS, SEM and IR spectral analysis of the deposit pointed out an organosilicon polymer structure, with a composition that is strongly affected by SiH₄ partial concentration. Possible routes involved in the SiH₄-photosensitized decomposition of Mo(CO)₆ are discussed. The laser technique can serve as an efficient method for creating metal-modified organosilicon polymers for membrane modification.

The time evolution of ablation and material transport during ArF excimer laser induced blow off of tungsten films from glass substrates is studied by fast photography using delayed dye laser pulses. The analysis of experimental results combined with heat flow calculations provides evidence that tungsten removal in the solid phase is the dominant mechanism in the 40 - 200 mJ/cm² fluence domain, while partially inhomogeneous melting is observed between 200 and 800 mJ/cm². In this fluence range, solid fragments and a halo consisting of molten droplets are observed indicating spatial separation of the two phases. The molten phase advances faster, forming a protective mist in front of the solid piece(s). At yet higher fluences (800 - 1000 mJ/cm²), a well separated solid phase could be recorded under the halo although model calculations suggest full vaporization of the layer. This unexpected phenomenon is explained by the optical shielding effect of the halo.

Laser treatment of the surface of materials is of major importance for many fields technology. One of the latest and most significant methods of this treatment is laser alloying consisting of introducing foreign atoms into the metal surface layer during the reaction of laser radiation with the surface. This opens up vast possibilities for the modification of properties of such a layer (obtaining layers of increased microhardness, increased resistance to electroerosion in an electric arc, etc.). Conductivity of the material is a very important parameter in case of conductive materials used for electrical contacts. The paper presents the results of studies on change in electrical conductivity of the surface layer of metals alloyed with a laser. A comparative analysis of conductivity of base metal surface layers prior to and following laser treatment has been performed. Depending on the base metal and the alloying element, optical treatment parameters allowing a required change in the surface layer conductivity have been selected. A very important property of the contact material is its resistance to plastic strain. It affects the real value of contact surface coming into contact and, along with the material conductivity, determines contact resistance and the amount of heat generated in place of contact. These quantities are directly related to the initiation and the course of an arc discharge, hence they also affect resistance to electroerosion. The parameter that reflects plastic properties with loads concentrated on a small surface, as is the case with a reciprocal contact force of two real surfaces with their irregularities being in contact, is microhardness. In the paper, the results of investigations into microhardness of modified surface layers compared with base metal microhardness have been presented.

The structure, phase composition and mechanical properties investigation results of the Fe-C system alloys synthesized under the influence of laser radiation are presented. The technological conditions of laser radiation with the alloy being synthesized from powder mixture and with carbon being doped into iron are discussed.

A high photo-sensitive area has been created in solid solution of Hg_1-xCd_xTe (x approximately equals 0.2) (MCT) without melting its surface. That idea of formation of heterojunction, which was indicated by computer modelling of mass transportation processes under laser treatment of MCT, is realized experimentally. MCT samples were irradiated with a Nd:YAG laser beam having an energy density 0.7 J/cm². The presence of a heterojunction not far below the upper surface has been verified by X-ray microanalysis.

The action of CO₂ laser (power density of 10³ - 10⁶ W/cm²) on silicates has been investigated. Spectroscopic, chemical and x-ray analysis of sublimates and irradiated zone made it possible to establish, that by laser action on these matters the selective excitation of localized vibrational mode up to breaking of covalent bonds with the selective sublimation of Si-O groups take place.

The principle of high power soft X-ray source design using laser plasma and waveguide X-ray optics is described. The radiation parameters of pulse and high-repetitive sources are reported. The experiments on X-ray induced effect on crystalline heteroepitaxial ZnSe/GaAs films are described.

The exposure of the back side of the YBCO thin film by one laser pulse (fluence 0.05 J/cm²) passed through the transparent substrate SrTiO3 leads to the partial removal of the irradiated film parts. The thickness of the residual layer does not exceed 50 nm and decreases with the increase of laser fluence. At 0.1 J/cm² the complete removal of the irradiated film parts take place. Numerical calculations show that the temperature arising in the film is about 600 degree(s)C, this is significantly below the melting temperature of YBCO compound. The film removal occurs possible due to thermal tension arising in the film and leading to its burst. The possibility of the partial removal may be explained by the shift of the temperature maximum near which the burst occurs into the film during the laser pulse The position of the temperature maximum at the end of laser pulse is in good agreement with the thickness of the residual layer. Possible applications of this low threshold thin film removal for the fabrication of devices based on high-temperature superconductors are discussed.

The most important problems to be solved lie in the generation of thermal stresses and the subsequent spalling of the coating. Now the method for improving the coating quality is to remelt the coating using a laser beam. This method can reduce the porosity and stresses and achieve proper microstructure and homogeneity. The Ni-Cr alloys were plasma sprayed onto A₃ steel substrates as bond coat with a layer of 50 approximately 100 micrometers thick. Alumina and/or zircoia powders were plasma sprayed onto the bond coat led to a 100 approximately 150 micrometers thick surface layer. The surfaces of the laser-treated coatings and prepared cross-sections were observed by optical microscopy and scanning electron microscopy. The relation between surface status of ceramic and laser process was discussed. The element permeability in ceramic coating and in bond coatings were discussed also.

A variation of CdTe photo- and cathodoluminescence after pulse laser irradiation has been investigated. It is shown that CdTe recombination characteristics changed only for the pulse energy exceeding a melting threshold. The laser irradiation regime resulting in an improvement of CdTe optoelectronic properties is found.

Over the last few years laser cutting has been widely introduced in industrial production lines, mainly due to the high processing speeds. In the present work a fundamental aspect of the cutting process of metals has been considered: the formation of periodic striations on the cut edge that greatly affects the quality of the treated samples. Therefore this paper is devoted to the study of the roughness of the cut surfaces with a particular attention to the dependence of this parameters on the working conditions. For a better understanding of the variables involved in the process, a comparison of the experimental data with the results of an analytical model has been performed. Furthermore a real time monitoring of the infrared emission coming from the interaction zone has been carried out by means of an electrooptic device properly developed for the measurements of the local temperature. A correlation between these data and the roughness measurements has been found.

The design and implementation of a software system for supporting laser material processing work is presented. The system integrates a database, numerical simulation and various other computer techniques and provides a user friendly environment. The general system structure is described. Research results on some related topics for the system design are also presented in this paper. This includes a neural network analysis on laser surface hardening and cladding, and the implementation of simulation models for cutting and welding of steel. A PC version of the software, named CALMP (Computer Assisted Laser Material Processing), is briefly described.