A 45 kW laser system was recently installed at 'Institut de Sourdure' in France in order to evaluate the possibilities of such high power beams in welding. Some results of welding various materials, different thicknesses and large components are presented. Some recent installations of high power laser equipments already integrated into production site or under development in ship building and steel fabrication are described. Finally, the objectives of an important research and development program launched recently for exploring the different aspects of laser welding in thick section steel fabrication is outlines.

Q-switched cw pumped Nd:YAG lasers provide high output power in combination with high peak power and high repetition frequencies. Welding highly reflecting materials, this operation mode should improve the coupling conditions of the laser beam. The experiments show a significant influence of the welding depth and the seam dimension. Furthermore, the beam quality is an important facto for the geometry of the welding seam. However at the achievable low spot diameters, the quality of the seam surface and the existence of pores reduce the advantage of this technique.

The modulation and duty cycle effects on Al-alloy welding with high power Nd-YAG laser are investigated. Micro- structural characterization of the low and high duty welds with wave modulation identified the differences in the weld morphology. Welding depth, undercut and strength of fusion zone are discussed as a function of the processing parameters.

Simultaneous laser beam welding is a modified procedure of both sided laser beam welding. Two laser beams are focused in opposite direction at the same time and place onto the workpiece. The process is characterized by the formation of a joint keyhole opened to both sides of the workpiece. The main advantages in comparison with conventional laser welding processes are higher welding speed, avoidance of angular distortion due to a symmetrical field of thermal stresses, as well as minimum porosity, especially in the middle of the seam volume, and a high degree of process stability. The advantages are depending on the joint keyhole. In the case of small adjustment of the two beam axes combined with inappropriate parameter settings this joint keyhole can collapse into two separated keyholes each having only an opening to one side of the workpiece. Therefore the process state with 'joint keyhole' has to be monitored. According to this criterion a non-destructive on- line measurement technique has been developed. The measurement technique is based on RF-frequency modulation of one of the two applied laser beams. Since the results of the measurement are available in very short time scales a usage for on-line control is possible.

The possibilities of pulsed laser welding of aluminium alloys monitoring are investigated. Simple finite element modeling of conduction and keyhole welding has been carried out. A complete instrumentation has been set up, including beam and plasma monitoring and impact shape and size measurements. This set up enables a real time monitoring of the seam and the detection of critical defects.

Tailored blank welding has been a rapidly growing segment of the automotive industry over the last five years. It allows to choose the optimal thickness of the sheets for different zones taking into account different mechanical stresses, vehicle safety reinforcement. Through the elimination of extra reinforcement parts, the use of tailored blanks allows to produce lighter car bodies and to simplify the production cycle. As more laser welding systems are being installed in industry, in order to increase the productivity and maintain constant quality of the products, the demand for the development of process monitoring systems increases. In this paper a monitoring system, based on the measurement of the radiation from the plasma plume during the CO₂ tailored blanks laser welding, is presented. Using an appropriate combination of optical components, detectors and a special software, a complete apparatus has been developed. The signals were found to be correlated to weld quality parameters including the defects such as holes, overlapping and open butts.

A review is reported of the various types of laser treatments which can be performed. The influence of infrared, visible and UV radiations on the surface composition, microstructure, morphology and properties of a lot of materials is investigated. Representative examples are given, to illustrate the various possibilities, e.g. laser cladding on metallic materials, remelting of ceramic, surface modification of ceramics for bonding to metals, surface amorphization of organic materials, formation of conductive area on polyimide films, and so on. Directions in which works are currently being pursued are mentioned.

CO lasers have potential advantages over CO₂ lasers due to the 5-6micrometers wavelength due the ability to transmit the energy through fiber-optic cables at powers < 100W and reduced plasma effects for welding applications. This paper describes the results obtained on a fast axial flow CO laser developed within EUREKA Project EU113 capable of operating at continuous output powers of 2.5kW for welding of mild steel. The results have shown that the CO laser has advantages in terms of weld penetrations achieved at low speeds at power levels of <2kW and less dependence on the type of shielding gas than a CO₂ laser.

Solid state nitriding of titanium under cw CO₂ laser was investigated. The nitriding kinetics were studied in the case of CO₂ laser treatment in isothermal conditions, and were compared to those obtained by using a conventional heating system. Identical kinetics rate constants and activation energy were obtained; therefore CO₂ irradiation of the titanium surface did not influence nitride growth. Studying nitriding treatment in non isothermal conditions showed that high heating rates induced modifications of the nitride morphology. At last, we investigated the evolution of the CO₂-surface coupling during the nitriding treatment. It was found that it depended only on the surface temperature and the substrate surface roughness since the growth of a few micrometers which nitride layer did not modify the coupling.

Potential applications such as hard facing of engine valve seat, turbine engine blade shroud interlock and leading edge of steam turbine blade, with controlled dilution have stimulated the use of laser cladding recently. In this paper, based on the laser beam interaction time, the microscopical study of dendrite structure formation in laser cladding of stellite number 6 on mild steel and Cr-Ni base materials is investigated. The effect of the various parameters such as heat input, beam interaction time, scanning frequency and transverse speed are considered. The applications in the rapid prototyping industries are also discussed.

The laser cladding process, which consists in adding a melt powder to a substrate in order to improve or change the behavior of the material against corrosion, fatigue and so on, involves a lot of parameters. In order to perform good tracks some parameters need to be controlled during the process. We present here a low cost performance system using two CCD matrix cameras. One camera provides surface temperature measurements while the other gives information relative to the powder distribution or geometric characteristics of the tracks. The surface temperature enables us to detect variations in the mass feed rate. Using such a system we are able to detect fluctuation of 2 to 3g/min in the mass flow rate. The other camera gives us information related to weak fluctuations within both gas flux. During the process, this camera is also used to perform geometric measurements. The height and the width of the track are obtained in real time and able the operator to find information related to the process parameters such as the speed processing, the mass flow rate. We display the result provided by our system in order to enhance the efficiency of the laser cladding process. The conclusion is dedicated to a summary of the presented works and the expectations for the future.

In order to obtain a good behavior in dynamic conditions, it is often necessary to manufacture surface alloys with conflicting properties, for example a high ductility combined with a high hardness or a high yield stress. Iron- base alloys with appropriated contents of manganese and carbon can be candidates for such requirements. Particular alloys, known as Hadfield steels, are of major interest. By using either Nd-YAG or CO₂ lasers, and by either injection of specific powder or remelting of a predeposited layer with a suitable composition, sound surface layers have been manufactured on steels with either a low or a high carbon content. These coatings with an austenitic structure have an elevated yield stress. After a presentation of the experimental procedures, the new surface alloys are characterized by using metallurgical observations, chemical analysis and mechanical tests.

A novel dry manufacturing process is proposed to replace some of the processing steps in the existing wet silver plating process. It involves the combination of high speed laser patterning and ablation techniques on a polymer masked copper leadframe. A Q-switched Ng-YAG laser with high speed scanning mirrors was initially used in this study. The suitable polymer coating for the relevant electroplating bath has been identified by immersion test and scanning electron microscopy. Process parameters such as scanning rate, protection gas, laser powder, beam size, working distance etc., were investigated. The effect of laser ablation and residual heat input upon the microstructure and properties of the metallic substrate were studied. The plating quality after laser patterning was also examined. A transparent organic film about 1.5 micrometers thick was found to be loosely adhered on the copper substrate regardless of the ablation conditions. This film created a major obstacle to the YAG laser ablation process proposed. Excimer laser was used to overcome this problem.

Surface effects induced by small laser impacts on a 55C1 steel were investigated in terms of the compressive residual stresses, the surface geometries and the work hardenings generated by the process. it was demonstrated that laser shock processing with 1-2 mm spot-size range could provide at least as beneficial surface effects as larger ones but limited to about 0.8 mm in depth where as large impacts affected more than 1.2 mm at the same power densities. This latter point was ascribed to differences in the chock propagation mode: shock decay was shown to occur earlier in the case of small impacts because of 2D attenuations as confirmed by Lagrangian simulations.

The purpose of this study was to evaluate the capacities of the pulsed YAG laser thick cutting on metallic material and to compare with the CO₂ laser capacities. Stainless steel cutting tests were made in air and underwater using CO₂ and YAG lasers. A performance assessment was made for each laser and the wastes produced in the cutting operation were measured and the gases and the aerosols analyzed. The results showed that the pulsed YAG laser is high performance tool for thick cutting and particularly attractive for nuclear applications.

Aircraft engine industry uses free running high power Nd:YAG lasers for drilling cooling holes into nickel base alloy turbine components. A cw-pumped, Q-switched, high beam quality laser system with 400W laser power is presented. The laser is used to trepan drilling of 1.6mm. Hastelloy X sheets and ceramic coated combustion chamber tubes of the same metal. Cylindrical shape, uniformity, and reproducibility are achieved with a trepan-like drilling setup. The heat load of the workpiece as well as the process time is considerably decreased by employing high-repetition Q-switched lasers.

This work presents a testing instrumentation which allows to determine important laser beam characteristics. The beam analyzer Laserscope UFF100 is moved along the laser propagation path and takes intensity profiles at several positions. With this 3D intensity data we determine the characteristics laser beam propagation parameters out of the result of a least square fit. The results show excellent agreement with the ordinary Gaussian beam propagation theory. The choose of the correct beam transforming optics, such as beam expanding telescopes or adaptive mirrors, can now easily be achieved in order to adapt the laser to its desired process.

In laser materials processing applications it is often necessary to work with uniform intensity distributions. This goal is quite difficult to achieve when dealing with high power laser beams, and becomes critical for a successful application involving surface heat treatment of non-metallic materials. We have designed and tested a very simple beam shaper for transforming the initial intensity distribution of a CO₂ laser beam mode into a more uniform intensity profile. The beam shaper is a tow-faceted mirror for active integration of high power coherent laser beams. After reflection in the faceted mirror, a TEM00 or TEM01 CO₂ laser beam is divided into two beamlets that overlap to give a more uniform intensity distribution. A sharp interference pattern due to the high spatial coherence of the incident beam appears. This interference pattern is actively integrated by a high-frequency longitudinal displacement of one of the facets. This provides a change in the relative phase of the two beamlets, and consequently the interference pattern vibrates and its contribution to the intensity distribution averages out. When sweeping this distribution over a sample, a uniform amount of energy is deposited at every point of its surface. It must be emphasized that unlike multifaceted mirrors, out two-facet integrator may provide uniform intensity profiles over any working distance. Finally, as in other integration devices an imaging system may be used to obtain a spot of the shape and the size desired for a particular application.

The design, fabrication and testing of a diffractive optical element for use in laser materials processing described. A 30mm diameter, Gaussian profile energy distribution from a 5KW carbon dioxide laser has been transformed into a rectangular energy distribution 6mm by 8mm at a distance of 500mm from the optic.

A laser-induced damage study on large-core, multimode fiber is presented. We develop a numerical analysis concerning high laser power transmission based on a beam ray tracing. Data are compared with experimental results obtained with a Nd-YAG laser and a step-index fiber. Studies of bulk damage in fiber show that the incident laser beam profile and the launching conditions are responsible of high-intensity sites inside the fiber. Gaussian and multimode spatial profiles are numerically investigated. Finally, we discuss optima laser characteristics to increase the energy transmission in the fiber.

High precision laser cutting permits a new approach for the conception and realization of complex miniaturized components and systems necessitating very high absolute dimensional and assembling precision. The laser cutting with a pulsed TEM00 Nd:YAG-slab laser results in mechanical tolerances and a reproducibility better than 3 micrometers over working areas of up to 30 X 30 mm². This permits not only to realize mechanical 2D-parts with very high dimensional precision but also the introduction of features for precise assembling of complex structures with very close tolerances without the need of delicate assembling procedures and machines. We present, as an example, an electrically steerable miniature mirror mount. In a volume of 10 by 10 by 4 mm³, a mirror with a clear aperture of 4 mm, an angular excursion of +/- 2 mrad and an axial excursion of 15 micrometers can be realized. The mechanical resonance lies between 200 and 600 Hz, depending essentially on the mirror mass and the stiffness of the flexure elements. Such a device can be used e.g. in laser resonators as passive or actively controlled mirror, in resonant cavities for SHG and THG or as a small Fabry-Perot spectrum analyzer.

The deep penetration laser welding is limited by the presence of a plasma on the working piece. This plasma absorbs a part of the power and defocuses the beam. The consequences are a loss in penetration and a wider weld. In order to avoid these phenomena, one can blow the plasma with a transverse gas jet. A model of deviation by jet has been developed and experimentally validated after a study ont eh gas jet behavior. Tests on gals blowing during laser welding on different materials show that the plasma could be suppressed using a lower gas flow rate than with the usual shielding systems. Furthermore, other gas than Helium, such as Argon, Nitrogen and even air could be used with the same performances. If they are mixed with an inert gas, the use of air or Nitrogen does not increase the oxidation or nitriding rate of the weld. The main effect of the blowing is a reduction of the weld width on its upper part, due to a decrease of the radiated heat and the defocusing. The heat affected zone is also reduced, which involves an increase of the mechanical resistance of the weld.

The model developed allows to know the temperature field in a cw Nd:YAG laser joining piece. To realize the model, a physical approach has been used for defining the heat sources. First, form a pressures balance the geometry of the keyhole is determined. Then an analysis of the plume existing at the surface of the target shows that the beam is scattered by the plume and consequently the heated area is enlarged. More a spectrometric characterization indicates that no ionized particles exist in the plume and certainly in the keyhole. So Fresnel absorptions are the predominant effects for energy absorption in the keyhole. This assumption is verified owing to Fresnel absorption coefficient measurements.

We study the laser-induced plume created during steel welding. The plume emission is measured with a spectrograph and a photodiodes array detector. We study the evolution of temperature and electron density for several welding parameters. Temperature and density calculations are based on the observation of line intensities and shapes. The other part of this study presents briefly a theoretical model which allows calculating the densities of each component of a complex plasma; like the one of stainless steel. These calculations yield the absorption of the laser energy in the plume.

An investigation was made of metastable states of overheated metal (mercury) when it s surface was exposed to nanosecond laser pulses. The dynamics of the thermodynamic state of mercury was analyzed on the basis of time-resolved measuring of an acoustic pulse propagating from the surface. The contribution of the vapor pressure was identified and the surface temperature was found as a function of time. The surface temperature was been obtain decrease exponentially with time after laser pulse action and the relaxation time was measured. The possibility of new-dynamic laser techniques of materials modification are discussed.

The new method of nondestructive remote control of a structure, material properties and defects in ear surface layers of construction materials is proposed. It is based upon laser excitation of surface acoustic waves (SAW) and its remote registration by detection of IR radiation, arising due to dilation temperature variation in SAW. Theoretical foundation of this technique is developed. The estimates show the reliability of the laser-induced surface acoustic waves; IR detection method. The method is especially convenient for investigation of a samples under elevated temperatures and with rough surfaces.

Laser shock processing (LSP) in water confinement regime was investigated for an incident 20-25 ns/40 J/(lambda) equals 1,064 micrometers pulsed laser beam. Experimental measurements of the shock wave temporal profiles induced by LSP have been performed with velocimetry interferometer system for any reflector. Above 10 GW/cm² the peak pressure is limited and the pulse pressure duration is reduced by parasitic plasma occurring in the confining water. The observation of the interaction zone with fast camera shows that the breakdown at the surface of the confining water is the only phenomena limiting the efficiency of the LSP. This plasma absorbs the incident laser energy and the power density reaching the target decreases. The duration of shock wave induced in the target is then shortened. This experiment explains the current limit of LSP in water confinement mode and opens new research field to understand the plasma effect at the surface of the confining water.

Laser-driven shock experiments in combination with VISAR technique have been performed to study the ablation pressure, the dynamic damage and spallation for aluminum targets with thicknesses in the 25-500 micrometers range. Shock- waves up to 100 kbar have been generated by laser irradiation intensities from 10¹⁰-10¹² W/cm² with a wavelength of 1.06 micrometers and pulses duration of 20-30 ns. The pressure profile has been determined using the laser-matter interaction code FILM, its amplitude has been compared with the one inferred by the VISAR velocity measurements. This temporal profile has been also used as a boundary condition applied at the front face of the target in the hydrodynamic code SHYLAC. Recorded free surface velocities from VISAR measurements exhibiting spallation features have been compared with numerical SHYLAC simulations to asses a continuous kinetic model of ductile spallation implemented in the code. Good agreement has been found between measured and predicted rear surface velocities for irradiation conditions leading to damage from void nucleation to complete spallation. Recovered samples have been examined by means of metallographic methods to compare the simulated damage with the experimental one tin terms of spall thickness and damage zone size.

Surface treatments with remelting have often irregular quality. This article presents on-line control of laser melting which induces an improved quality of the treatment and more regular results. In order to build up a regulator, different sensor have been experimented. Responses are analyzed versus static and dynamic process commands. The molten depth is estimated on-line from molten pool dimensions measured by the CCD camera and image on-line processing. A state model is developed. The system is controlled by three variables: sample velocity, laser power and intensity distribution. The outputs of the system are the depth and width of the melted zone, and the temperature field. The commands and the outputs are chosen in accordance with the application under consideration. Therefore the process has been regulated.

An excimer laser source was used for shock treatment of metals. The treated specimens were materials applied in automotive and aeronautical industry. The process was investigated with physical methods and optimized in terms of high surface pressures. The results of the shock treatment concerns the modifications of the mechanical properties such as roughness, hardness and residual stresses.

In industry, infrared lasers are well established in the area of macroscopic material processing today due to their high flexibility and integrability. Even in the years of recession the laser market grew more than 10 percent per year. For several years now precision machining with lasers has obtained a worldwide growing interest. Copper vapor lasers are favorable for precision machining because of their pulse duration, wavelength and bean quality. The present work reports on the improvements in reliability of copper vapor lasers for industrial use. The relevant criteria of precision machining are outlined and typical applications are presented.

Thin amorphous C-N films were deposited on silicon substrates at room temperature by XeCl laser ablation of graphite in low pressure nitrogen and ammonia atmospheres. The deposition rates decrease with increasing ambient pressure. Films deposited in NH₃ are thinner than films deposited in N₂ at the same ambient pressure, their N/C atomic ratios are higher, but they present a lower quantity of N atoms bound to C atoms. Different diagnostic techniques were used to characterize the deposited films, which result homogeneous, hard and present a high electrical resistivity.

Due to its important chemical stability, polyether- etherketone (PEEK) thermoplastic presents poor adhesive bonding properties. The possibilities of enhancing the PEEK adhesive properties by excimer laser pretreatments are investigated. Surface modifications are characterized, depending on the experimental working conditions, using SEM, profilometry, XPS, wettability and mechanical tests. In the case of an excimer laser pretreatment, the induced surface modifications are dependent on the energetic density of the incoming laser beam: (1) for E > E ablation threshold, surface ablation occurs. The treated surface is characterized by an considerable roughness increase, a carbon content enrichment and a decrease of wettability. The adhesive bounding properties are very significantly increased. (2) For e < E ablation threshold, the treatment induces superficial thermal and chemical modifications. Surface amorphization, formation of new 0-C equals O bonding, decrease of the C-O and C equals O bonding and a decrease of the shake up signal. The increase of the water wettability is more pronounced when the treatment gas contains oxygen. A cohesive failure in the adhesive was obtained when treatment is achieved using argon gas whereas an adhesive failure at the interface may be evidenced when air is used. Lap shear strength values show that excimer laser irradiation improve PEEK adhesion bonding properties for all treatment conditions.

Spring barley, winter wheat and maize seeds were subjected to the action of He-Ne laser irradiation having a low intensity in the visible region of the spectrum (628-640 nm) in conjunction with magnetic fields. The following results were obtained: laser irradiation with magnetic fields induced activation of the natural plant defence/immune systems gave the harvest crop level increased to about 50- 300 percent; a correlation was established between the rate of the fungal pathogens growth and the stimulation of plant immunity after the seeds had been treated with laser irradiation and magnetic field.

Plasma plume generated during laser ablation of Y, YBaCuO, GaAs, and InAs targets was investigated by laser-induced fluorescence technique. Time-of-flight method was used. The velocity distribution functions of atoms, ions, and atoms in metastable states were obtained. Two regimes of plasma expansion were observed. In the first regime the plasma expands in vacuum as ideal gas, and in the second one the acceleration of ions by inner plasma electrical field takes place. The bimodal velocity distribution of plasma particles is the main feature of the second regime. Also two regions in plasma plume were observed: 'collisional' and 'collisionless'. The first region is placed in vicinity of a target. Its dimension is about 30 mm and does not depend on laser fluence. In this region recombination processes and transformation of velocity distribution takes place. In the second region velocity distribution functions are not changing. Stable shapes of velocity distribution functions is a feature of the second region. It is well known that during laser ablation the drops appear in plasma plume. The concentration and velocity of drops generated during laser ablation of target were measured. The drops velocity is about 10 times less than atoms. So it is possible to separate drops from atomic component in laser plasma. The mechanical chopper was used for drops removing. The drops' concentration on films deposited with chopper was negligible.

When high quality laser beam are combined with suitable imaging optics and manipulation systems, laser micro machining offers excellent solutions to industrial needs. In this context the presented work was performed to demonstrate the potential of the copper vapor laser for upcoming applications. Therefore, a systematic series of laser beam cutting, drilling and milling experiments were carried out using copper sheets of thickness between 0.01 mm and 0.250 mm. In a first step zero-dimensional, 1D and 2D structures were generated with depth/width ratios varying from 1:100 to 10:1 using different processing strategies. The results have been characterized in terms of the minimal geometrical deviations and processing speeds achievable.

In this work we present the results of CVD-diamond processing using a copper vapor laser. With a self filtering unstable resonator the laser produces an average power of 9 watts in a 3.5 times limited diffraction beam at a 10 KHz repetition rate. The laser beam is focused on the diamond surface using a lens with a 150 mm focal distance producing a spot size of 70 microns. The laser intensity achieves 2 GW/cm² on the focus. Electronic microscopy of the processed samples showed clean cut and drill with the whole diameter coincident to the laser beam spot size. Since diamond has a very high thermal diffusivity the temperature rise due to the average power would not be enough to promote evaporation, thus it was concluded that the diamond processing is only die to the laser peak power. Diamond burr with 1.0 mm diameter were cut with the same apparatus at a linear velocity of 200 mm/hour showing a clear and shape cut.