This PDF file contains the front matter associated with SPIE Proceedings Volume 8963, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Laser remote processing is used in a wide field of industrial applications. Among other things, it is characterized by flexible beam guidance in combination with high processing velocities. But in most cases process gas support in the interaction zone is omitted. Consequently, interaction mechanism between the vapor plume and the incident laser radiation can dynamically affect the process stability. Referring to remote welding with high brilliant laser sources having a wavelength around 1 μm, the interaction between the incident laser radiation and formed particles plays an important role. The presented work shows results of the investigation of the laser-induced particle formation during the laser welding of stainless steel with a 2 kW fiber laser under remote conditions. It is therefore concentrated on the dynamical behavior of the laser-induced particle formation and the dependence of the particle formation on the laser beam power. TEM images of formed particles were analyzed. In addition, the radiation of a LED was directed through the vapor plume. On the one hand, the dynamic of the attenuation was considered. On the other hand, the Rayleigh approximation was used in order to evaluate the detected signals.

Multi-material structures pose an attractive option for overcoming some of the central challenges in lightweight design. An exceptionally high potential for creating cost-effective lightweight solutions is attributed to the combination of steel and aluminum. However, these materials are also particularly difficult to join due to their tendency to form intermetallic compounds (IMCs). The growth of these compounds is facilitated by high temperatures and long process times. Due to their high brittleness, IMCs can severely weaken a joint. Thus, it is only possible to create durable steel-aluminum joints when the formation of IMCs can be limited to a non-critical level. To meet this goal, a new joining method has been designed. The method is based on the combination of a continuous wave (pw) and a pulsed laser (pw) source. Laser beams from both sources are superimposed in a common process zone. This makes it possible to apply the advantages of laser brazing to mixed-metal joints without requiring the use of chemical fluxes. The double beam technology was first tested in bead-on-plate experiments using different filler wire materials. Based on the results of these tests, a process for joining steel and aluminum in a double-flanged configuration is now being developed. The double flanged seams are joined using zinc- or aluminum-based filler wires. Microsections of selected seams show that it is possible to achieve good base material wetting while limiting the growth of IMCs to acceptable measures. In addition, the results of tensile tests show that high joint strengths can be achieved.

Continuous application development in combination with advancements in laser sources and accessories enabled several trends in laser material processing. This paper will show investigations in process understandings based on modern process diagnostics like high speed videos. We will focus on applications related to thick sheet welding, welding with wobbling techniques, hot forming materials and dissimilar materials. Additionally we link the gained process understandings to possibilities how to successfully introduce the knowledge in industrial applications.

We have developed heat resistant strain sensors using laser processing techniques. The application is aimed at structural health monitoring for high temperature piping systems. This situation requires extraordinary durability such as radiation resistance and noise isolation due to adverse conditions caused by nuclear reactions or electro-magnetic pulses. We proposed that a Fiber Bragg Grating (FBG) sensor made by femtosecond laser processing could be the best candidate. The combination of fabric reinforcement and a heatproof adhesive mold successfully protected the fragile optical fiber once the fiber was installed on the piping material’s surface. To make the best use of the heat-resistant characteristic, we fixed the FBG sensor by metal mold. A groove was processed onto the surface of a SUS metal plate with a grindstone. We used a Quasi-CW laser to weld a filler wire onto the plate. The optical fiber was situated under the filler wire before was heated by laser pulses with 10 joule energy and a duration of 10 ms. A series of weld pool formed a sealing clad on the groove. The FBG sensor was buried at a depth of 1 mm over a length of 1 cm. No degradation in its reflection spectra was detected before and after the processing. The FBG sensor can detect the vibration of the plate caused by impact shocks. In this paper, the Bragg peak shift of the FBG sensor under laser cladding condition has been discussed.

Surface hardening with discrete laser spot treatment is an interesting solution since the adoption of a single pulse allows the treatment of different surface geometries avoiding the effect of back tempering. The aim of this work is to find a suitable process window in which operate to get best results in terms of hardness, diameter and depth of the treated region. A single pulse out of a fiber laser source impinging on a bearing hypereutectoid steel was used using different power values, pulse energy and defocussing distances, in order to get the optimal process parameters. The dimensions of the hardened zone and its hardness were then acquired and related to the laser process parameters, to the prior microstructure of the steel (spheroidized and tempered after oil quenching) and to the roughness on the specimen before the laser treatment. Experimental results highlighted that both the surface condition (in terms of roughness) and the initial steel microstructure have a great influence on the achieved hardness values and on the dimension of the laser hardened layer. The pulse energy and power strongly affected the dimension of the hardened layer, too.

A new process, based on ring spot geometry, is presented for laser surface hardening of large cylindrical com-ponents. The proposed technique leads to a very hard, deep and uniform treated area along the entire work piece surface without introducing a tempered zone, making the process very attractive compared to conventional induction hardening that exhibits both low energy efficiency and poor flexibility. A complete physical model is presented for the process, together with a study of the influence of process parameters on the final outcome. The results of an extensive validation campaign, carried out following the AISI1040 standard, are also reported.

As available power levels from both fiber and disc lasers rapidly increase, so does the need for more robust beam delivery solutions. Traditional transmissive optics for 1 micron lasers have proven to be problematic in the presence of higher power densities and are more susceptible to focal shift. A new, fully-reflective, optical solution has been developed using mirrors rather than lenses and windows to achieve the required stable focal spot, while still protecting the delicate fiber end. This patent-approved beam focusing solution, referred to as high power reflective focusing optic (HPRFO), involves specialty mirrors and a flowing gas orifice that prevents ingress of contaminants into the optically sensitive region of the assembly. These mirrors also provide a unique solution for increasing the distance between the sensitive optics and the contamination-filled region at the work, without sacrificing spot size. Longer focal lengths and lower power densities on large mass, water-cooled, copper mirrors deliver the robustness needed at increasingly high power levels. The HPRFO exhibits excellent beam quality and minimal focal shift at a fraction of commercially available optics, and has demonstrated consistent reliability on applications requiring 15 kW with prolonged beam-on times.

Transmitting high power laser light through fiber optic cables has been used in industrial environments for years. Designing fiber optic cables for industrial environments requires robust solutions able to handle high power losses without compromise either to process quality or to safety. Internal water cooling, where the optical fiber is in direct contact with water, in combination with an efficient cladding mode-stripper the optical fiber cable has superior advantages handling high power losses. In this paper we will present recent power-handling data for the new series of the well-known standards QBH and QD (LLK-D) fiber optic cables launched by Optoskand. The new series are designed with a combination of materials and internal water cooling.

High power laser beamshapers based on lens arrays are widely used to generate square, rectangular or hexagonal flat-top far-field beam profiles. These devices can provide high efficiency and excellent brightness preservation, but offer a limited range of far-field profiles and can suffer from diffraction-related artefacts when used with spatially-coherent beams. Diffractive optical elements (DOE) offer a far wider range of far-field profiles, and better speckle behavior, but bring performance trade-offs in terms of brightness, efficiency, scattered power and residual zeroth-order power. Freeform refractive optics offer additional choices in the design of high power laser beamshapers. Freeform lens arrays offer a wider range of beam profile options than that available from catalogue lens array parts. Freeform field mapping beamshapers can generate a wide range of application-specific beam profiles with high efficiency and, where required, minimal reduction in brightness. More complex quasi-random freeform surfaces can act as a pseudorandom refractive intensity mapping element (PRIME), providing a level of beamshaper design flexibility closer to that of DOEs, but without the related high-order scatter and zeroth order leakage. We describe the design and implementation of these different types of refractive beam shaper in fused silica, using PowerPhotonic’s direct-write freeform fabrication process. This is ideal for use in high-power laser systems, where high damage threshold and low loss are essential. We compare and contrast the performance, benefits and limitations of these types of beamshaper, and describe how to select the ideal beamshaper type based on source coherence properties and application beam profile requirements.

Micro optic components such as the fast axis collimator (FAC) are in widespread use in the high power diode laser industry. The requirement of high numerical aperture from diode laser and optical design and the pressure of cost to performance ratio have created convergence in the application towards the design of a plano-aspheric cylinder lens with high refractive index. The performance in power transmission and optical collimation of the FAC lens type are dependent on specific factors such as accuracy in form and refractive index, surface roughness and performance of the coating. We present a qualified method for measurement of the collimation efficiency and industrial analysis of the form error, of the surface roughness, of the AR coating as well as the result of a 1000h damp/heat test of the stability of the AR coating.

In complex laser systems, such as those for material processing, and in basically all laboratory applications passive optical components are indispensable. Matching beam diameters is a common task, where Galileo type telescopes are preferred for beam expansion. Nevertheless researches and customers have found various limitations when using these systems. Some of them are the complicated adjustment, very small diameter for the incoming beam (1/e²), fixed and non-modifiable magnifications. Above that, diffraction-limitation is only assured within the optical design and not for the real world setup of the beam expanding system. Therefore, we will discuss limitations of currently used beam expanding systems to some extent. We will then present a new monolithical solution, which is based on the usage of only one aspherical component. It will be shown theoretically how the beam quality can be significantly improved by using aspherical lenses. As it is in the nature of things aspheres are working diffraction limited in the design, it will be shown how to combine up to five monolithical beam expanding systems and to keep the beam quality at diffraction limitation. Data of the culminated wavefront error will be presented. Last but not least insights will be given how beam expanding systems based on aspheres will help to use larger incoming beams and to reduce the overall length of such a system.

For many applications, such as spectrometers and high power lasers, roughness is an important parameter that has been discussed again and again. Especially for high power systems, the surface quality is crucial for determining the damage threshold and therefore the field of application. Every application has different needs with respect to roughness, while most of them have additional needs as regards surface defects and waviness as well. For high power lasers, it is important to reduce absorption and scatter light, as absorption increases the temperature of the elements, which results in movement of the optical focus (thermal lensing) or, even worse, damage to the lens. This paper will focus on roughness, especially because the specific roughness for aspherical elements is very different compared with spherical/plano surfaces. Furthermore, it has often been difficult to compare roughness measurements because of different measurement methods and the usage of filters and surface fits. Measurement results differ significantly depending on filters and, in particular, on the size of the measured surface. Insights will be given as to how values behave depending on the quality of the surface and the size of the measured area. Most of these applications also require low roughness on aspheric surfaces. Because of small tool sizes in aspherics, it has not yet been possible to achieve the same low level as for spheres and plano optics. In addition, the results of a new manufacturing process will also be shown, allowing low roughness on aspherics, even with a remarkable departure from the best-fit sphere.

We demonstrate intra-fiber couplers performance that is close to complete brightness preservation up to 3kW. Furthermore, when mutually coherent sources were used, the same couplers were able to achieve brightness enhancement with almost no beam quality (BQ) deterioration. The couplers are based on an adiabatic, all-fiber, mode coupling device preserving the lowest spatial mode orders. Brightness levels that approach the theoretical limits were achieved by compressing the participating modes into a tight cross section. Incoherent combination is shown for 2×1, 3×1 and 7×1 combined elements. Additionally, we present a solution for preserving the beam propagation factor of the coupler by using a specialty engineered core delivery fiber. The fabricated components are fully fiber- integrated, hence, without free-space limitations. An overall transmission of <90% was obtained, while the coupler-delivery connection is responsible for less than 0.5% loss. Consequently, relatively low temperatures were observed in the combiner package. Alternatively, utilizing two mutually coherent sources, a quadratic brightness factor improvement was demonstrated. The scheme does not require polarization preserving fibers, and achieved rugged 'in-phase' mode-locking. This allows for a significantly simplified scheme, compared to common coherent combining methods. Prospect on future trends relating to nonlinearities and thermal load management are discussed.

Laser technology has been used in manufacturing in industry since the late 1960s. Industry and GE businesses have leverage laser welding for productivity gains, cost savings, and quality. The presentation will high light several laser-based welding applications, old and new. Applications will include the welding of refractory materials (e.g. Mo and Nb) for lighting products; 40 foot long fuel rods are welded with 2 kW fiber lasers for the nuclear business; head-liner welding for the diesel engine for locomotives (14 kW fiber laser replaced CO2 laser); and X-ray components are welded in a two-station 11kW fiber laser (EB welding replaced by laser). The three fiber laser applications were all transitioned into GE businesses during 2011 and it demonstrates the emergence of fiber laser welding being used in GE for manufacturing, processing.

Laser drilling is a highly efficient technique to generate holes in almost any material. The relatively small amount of heat being involved during the process results in a small heat affected zone. This characteristic makes laser processing interesting for composite materials. The drilling process has to be adapted to the special characteristics of the composite material. In this paper investigations were performed with an advanced composite material, that is a metallic hollow sphere structure (MHSS). Numerical simulation was used to predict heat flux and temperature levels for different geometric parameters of the spheres (diameter, wall thickness) in order to optimize the drilling process. The numerical simulation allows a detailed analysis of the physical process in the zone that is influenced by the laser beam, which can hardly be analyzed by any measuring technique. The models for transient numerical analysis consider heat conduction and convection. The experimental work was done by a CO₂-laser. The percussion drilling method has been used as drilling technique. The pulse duration was in the millisecond time regime. Investigations have been done with a mean power of 100 W, 200 W and 400 W. Two focal lenses have been used with focal lengths of 5.0´´ and 7.5´´. The laser beam melts the hollow sphere structure inside the beam leaving a hole in the structure as well as in individual hollow spheres. An image processing technique was developed to determine the circularity on the spheres and the drilled diameter in the structure. The circularity declines with increasing drill depth. The diameter as function of depth can be well described with lines of constant intensity of the focussed laser beam, the isophotes.

Forging tools for aluminum work pieces show an increased adhesive wear due to cold welding during the forging process. Laser dispersing offers at this point a great potential to fabricate protective layers or tracks with tailored properties that reduce abrasive or adhesive wear at the surface of highly stressed components. Using different process strategies, four metal ceramic compounds applied on two substrate geometries were investigated regarding their structural and mechanical properties and their performance level. The subsequent forging tests have pointed out a positive effect and less adhesive residuals on the laser dispersed tool surface.

In various modern scientific and industrial laser applications, beam-shaping optics manipulates the laser spot size and its intensity distribution. However the designed laser spot frequently deviates from the design goal due to real life imperfections and effects, such as: input laser distortions, optical distortion, heating, overall instabilities, and non-linear effects. Lasers provide the ability to accurately deliver large amounts of energy to a target area with very high accuracy. Thus monitoring beam size power and beam location is of high importance for high quality results and repeatability. Depending on the combination of wavelength, beam size and pulse duration , laser energy is absorbed by the material surface, yielding into processes such as cutting, welding, surface treatment, brazing and many other applications. This article will cover the aspect of laser beam measurements, especially at the focal point where it matters the most. A brief introduction to the material processing interactions will be covered, followed by fundamentals of laser beam propagation, novel measurement techniques, actual measurement and brief conclusions.

The effort for reduced cycle times in manufacturing has supported the development of remote welding systems which use a combination of scanners for beam delivery and robots for scanner positioning. Herein, close coupling of both motions requires a precise command of the robot trajectory and the scanner positioning to end up with a combined beam delivery. Especially the path precision of the robot plays a vital role in this kinematic chain. In this paper, a sensor system is being presented which allows tracking the motion of the laser beam against the work piece. It is based on a camera system which is coaxially connected to the scanner thus observing the relative motion of the laser beam relative to the work piece. The acquired images are processed with computer vision algorithms from the field of motion detection. The suitability of the algorithms is being demonstrated with a motion tracking tool which visualizes the homogeneity of the tracking result. The reported solution adds cognitive capabilities to manufacturing systems for robot scanner based materials processing. It allows evaluation of the relative motion between work piece and the laser beam. Moreover, the system can be used to adapt system programming during set-up of a manufacturing task or to evaluate the functionality of a manufacturing system during production. The presented sensor system will assist in optimizing manufacturing processes.

An innovative optical train for a selective laser melting based manufacturing system (SLM) has been designed under the objective to track the course of the SLM process. In this, the thermal emission from the melt pool and the geometric properties of the interaction zone are addressed by applying a pyrometer and a camera system respectively. The optical system is designed such that all three radiations from processing laser, thermal emission and camera image are coupled coaxially and that they propagate on the same optical axis. As standard f-theta lenses for high power applications inevitably lead to aberrations and divergent optical axes for increasing deflection angles in combination with multiple wavelengths, a pre-focus system is used to implement a focusing unit which shapes the beam prior to passing the scanner. The sensor system records synchronously the current position of the laser beam, the current emission from the melt pool and an image of the interaction zone. Acquired data of the thermal emission is being visualized after processing which allows an instant evaluation of the course of the process at any position of each layer. As such, it provides a fully detailed history of the product This basic work realizes a first step towards self-optimization of the manufacturing process by providing information about quality relevant events during manufacture. The deviation from the planned course of the manufacturing process to the actual course of the manufacturing process can be used to adapt the manufacturing strategy from one layer to the next. In the current state, the system can be used to facilitate the setup of the manufacturing system as it allows identification of false machine settings without having to analyze the work piece.

This presentation deals with a camera based seam tracking system for laser materials processing. The digital high speed camera records interaction point and illuminated work piece surface. The camera system is coaxially integrated into the laser beam path. The aim is to observe interaction point and joint gap in one image for a closed loop control of the welding process. Especially for the joint gap observation a new image processing method is used. Basic idea is to detect a difference between the textures of the surface of the two work pieces to be welded together instead of looking for a nearly invisible narrow line imaged by the joint gap. The texture based analysis of the work piece surface is more robust and less affected by varying illumination conditions than conventional grey scale image processing. This technique of image processing gives in some cases the opportunity for real zero gap seam tracking. In a condensed view economic benefits are simultaneous laser and seam tracking for self-calibrating laser welding applications without special seam pre preparation for seam tracking.

We have integrated an imaging thermographic sensor into commercial welding optics for observation of the weld zone. Key element of the sensor is an InGaAs-camera that detects the thermal radiation of the welding process in the wavelength range of 1,200 to 1,700 nm. This is well suited to record images of the keyhole, the melt pool and the thermal trace. The sensor was integrated to the welding heads for on-axis observation to minimize the interfering contour to ensure easy adaption to industrial processes. The welding heads used were established industrial-grade TRUMPF optics: a BEO fixed optics with 280 mm focal length, or a TRUMPF PFO-3D scanner optics with 450 mm focal length. We used a TRUMPF TruDisk 16002 16kW-thin disk laser that transmits its power through a 200 μm core diameter light cable. The images were recorded and features of the various process zones were evaluated by image processing. It turns out that almost all weld faults can be clearly detected in the NIR images. Quantitative features like the dimension of the melt pool and the thermal trace can be derived from the captured images. They are correlated to process input parameters as well as to process results. In contrast to observation in the visible spectrum the NIR camera records the melt pool without auxiliary illumination. As an unrivaled attribute of the NIR sensor it supports an online heat flow thermography of the seam and allows identifying missing fusion (“false friends”) of lap joints virtually during the welding process. Automated weld fault detection and documentation is possible by online image processing which sets the basis for comprehensive data documentation for quality assurance and traceability.

Continuous carbon fibre reinforced plastics (CFRP) are recognized as having a significant lightweight construction potential for a wide variety of industrial applications. However, a today‘s barrier for a comprehensive dissemination of CFRP structures is the lack of economic, quick and reliable manufacture processes, e.g. the cutting and drilling steps. In this paper, the capability of using pulsed disk lasers in CFRP machining is discussed. In CFRP processing with NIR lasers, carbon fibers show excellent optical absorption and heat dissipation, contrary to the plastics matrix. Therefore heat dissipation away from the laser focus into the material is driven by heat conduction of the fibres. The matrix is heated indirectly by heat transfer from the fibres. To cut CFRP, it is required to reach the melting temperature for thermoplastic matrix materials or the disintegration temperature for thermoset systems as well as the sublimation temperature of the reinforcing fibers simultaneously. One solution for this problem is to use short pulse nanosecond lasers. We have investigated CFRP cutting and drilling with such a laser (max. 7 mJ @ 10 kHz, 30 ns). This laser offers the opportunity of wide range parameter tuning for systematic process optimization. By applying drilling and cutting operations based on galvanometer scanning techniques in multi-cycle mode, excellent surface and edge characteristics in terms of delamination-free and intact fiber-matrix interface were achieved. The results indicate that nanosecond disk laser machining could consequently be a suitable tool for the automotive and aircraft industry for cutting and drilling steps.

The additional weight of the batteries in electric cars can be compensated by using carbon fiber reinforced plastics (CFRP) for structural parts of the passenger cell. Various machining processes for CFRP are currently subject to investigations. Milling and abrasive waterjet cutting implicate fiber pull out or delamination and, thus, do not thoroughly meet the requirements for mass production. Despite this, laser beam cutting has a great potential in large scale cutting of CFRP and is a predominant research topic. Remote laser beam cutting especially provides a good cut surface quality. Currently, the correlation between cutting parameters and edge quality is not sufficiently known. In particular, studies on the dynamic strength of remote laser cut parts are missing. Therefore, fatigue testing was performed with specimens cut by laser radiation and the results were compared with others made by milling and abrasive waterjet cutting. With these experiments, a comparable study of the different methods of CFRP cutting was achieved. The influence of both the heat affected zone (HAZ) and of defects like micro-fissures on the fatigue strength were evaluated.

In the automotive industry as well as in other industries ecological aspects regarding energy savings are driving new technologies and materials, e.g. lightweight materials as aluminium or press hardened steels. Processing such parts especially complex 3D shaped parts laser manufacturing has become the key process offering highest efficiency. The most established systems for 3D cutting applications are based on gantry systems. The disadvantage of those systems is their huge footprint to realize the required stability and work envelope. Alternatively a robot based system might be of advantage if accuracy, speed and overall performance would be capable processing automotive parts. With the BIM “beam in motion” system, JENOPTIK Automatisierungstechnik GmbH has developed a modular robot based laser processing machine, which meets all OEM specs processing press hardened steel parts. A benchmark of the BIM versus a gantry system was done regarding all required parameters to fulfil OEM specifications for press hardened steel parts. As a result a highly productive, accurate and efficient system can be described based on one or multiple robot modules working simultaneously together. The paper presents the improvements on the robot machine concept BIM addressed in 2012 [1] leading to an industrial proven system approach for the automotive industry. It further compares the performance and the parameters for 3D cutting applications of the BIM system versus a gantry system by samples of applied parts. Finally an overview of suitable applications for processing complex 3D parts with high productivity at small footprint is given.

The power level of Yb doped fiber lasers which operate in continuous wave mode has been increasing in recent years and various kinds of applications using high power single-mode fiber lasers that oscillate in 1microns wavelength range were reported. Single-mode fiber laser that has excellent beam quality of less than 1.1 M² value with kW class average power can be focused to tens of microns diameters and its optical power density at the focus point is more than 1×10⁸ W/cm². In this power density range, the interaction between 1microns laser light and matter, not only metal materials but non-metal materials, is completely different from that of lower level. The power density initiates laser processing of copper that has relatively high reflectivity at this wavelength range among metals and alumina base plate with over 90% reflectivity. Other interesting material which can be processed by this energy level is carbon fiber reinforced plastics (CFRP). On the other hand, for industrial application and further processing investigation, modulation speed is one of the most important factors because that relates to processing speed and precise control of laser energy input to a material. In this paper, we report on the power dependence of some material processing of copper wafer welding, alumina base plate scribing, and CFRP cutting using single-mode fiber laser which is capable of over 1kW peak power operation and has rapid switching time below 5 micro seconds.

The most extensively used lasers for aluminum and its alloys cutting, are CO₂ and Nd:YAG operating in continuous wave and pulsed mode. High power solid state fiber lasers operating in continuous wave mode offer a great potential in improving the cut quality and productivity of highly reflective materials cutting process due to the better absorptivity of 1 μm laser radiation. The high processing speeds of CW mode and a good cut quality could be achieved at the same time. In this work, cutting experiments were performed on Al1050 1mm thick sheets using a fiber laser and Nitrogen as assist gas. A DOE approach that consists of fitting the regression models by means of response surface method (RSM) was adopted. The effects of cutting speed, focal position and assist gas pressure on dross height, kerf width and roughness parameters were investigated. Results showed that processing in CW with fiber laser increases the cutting speed and gives a cut quality comparable with results obtained with CO₂ and Nd:YAG lasers and reported in literature.

The reasons of occurrence of the primary aberrations in optical systems for high-power-technology lasers have been analyzed. The laser intensity profile transformation in presence of a primary aberration of the both signs has been studied. A number of the optical systems with completely the same optical parameters except uncorrected primary aberration has been designed. The influence of laser intensity profile produced by these systems on the quality of midpenetrating laser cutting has been examined. It has been found that good quality cuts may be obtained for every shape of the laser intensity distribution. However, the more the scale of an uncorrected aberration is the more accurate the focal point position has to be maintained.

The conditions of minimal-roughness surface production were studied experimentally in the process of the oxygenassisted laser cutting with the fiber and СО₂ lasers. The coefficient of the laser radiation absorption in the cut channel during the cutting process was measured as the sheet thickness varied from 3 to 16 mm. It is demonstrated that the cutting conditions with the minimal roughness can be formulated for the two laser types with the same generalized parameters, i.e. dimensionless absorbed laser power and Peclet number (dimensionless speed). Numerical values of these parameters were found experimentally. The optimum Peclet number is 0.5 for the СО₂-laser cutting, and 0.35 when the fiber laser is used.

We have been developing a new laser cladding system to repair the damages of parts in aging plants. It consists of some devices which are a laser torch, composite-type optical fiber, QCW fiber laser and etc. All devices are installed in a mobile rack, so we can carry it to plants, laboratories or anywhere we want to use. We should irradiate the work with the best accuracy of laser beam and filler wire in laser cladding. A composite-type optical fiberscope is useful. This fiberscope was composed of a center fiber for beam delivery surrounded by 20000 fibers for visible image delivery. Thus it always keeps target on center of gun-sight. We succeeded to make a line laser cladding on an inside wall of 1-inch tube by our system. Before this success, we solved two serious problems which are the contamination of optics and the deformation of droplet. Observing laser cladding process by X-ray imaging with Spring-8 synchrotron radiation, we found that the molten pool depth was formed to be under a hundred micrometers for 10 milliseconds. A Quasi-CW fiber laser with 1 kW was employed for a heat source to generate the shallow molten pool. The X-ray shadowgraph clarified that a molten droplet was formed at the edge of a wire up to a millimeter size. It grew up if the wire didn’t contact with the tube wall in initial state. Here we succeeded to measure the thermo-electromotive force voltage between a wire and a tube metal to confirm whether both came in contact. We propose to apply the laser cladding technology to the maintenance of aging industrial plants and nuclear facilities.

The process of Selective Laser Melting (SLM) is an innovative technology for rapid prototyping that can be included among the SFF (Solid Freeform Fabrication) techniques, which are characterized by "free-form" manufacturing of solid parts. SLM is an additive technology that operates starting from the data encoded in the three-dimensional computer aided design (CAD) file of the component to be built. After the slicing operation made on the 3D model of the component, the consequent data file is sent to a computer-controlled laser device that fuses successive layers of metal powder to create the three-dimensional product. The SLM is a technological process which involves optical, thermal and solidification phenomena; thus the analysis of the process is rather complex. This work aims to study the molten/solidified zone in SLM samples through the experimental analysis of the shape and the size of laser tracks. The functional relationships between dimensional parameter of the molten/solidified track and the main parameters used to control the process was identified.

We present a photothermal reflectance microscopy for detecting local defects inside optical films. This technique employs CCD-based thermoreflectance microscopy, which measures temperature-dependent optical reflectivity changes of materials. For photothermal imaging, an 808 nm CW laser beam with sinusoidal modulation is used to heat absorbing defects in the transparent optical film. The thermo-optic response resulting from the laser beam absorption of defects in the material yields a periodic alteration in the reflectivity around the defects. Such a time-varying thermoreflectance signal is probed with a 636 nm LED, and the amplitude of this signal is detected using a homodyne lock-in detection scheme, permitting enhancement of the defect contrast. The feasibility of the proposed imaging system is demonstrated on an optical material having absorbing inclusions, showing that the variation of the normalized optical reflections clearly reveals the local distribution of the submicron-sized defects buried in the optical material.

The production of complex titanium components for various industries using laser welding processes has received growing attention in recent years. It is important to know whether the result of the cohesive joint meets the quality requirements of standardization and ultimately the customer requirements. Erroneous weld seams can have fatal consequences especially in the field of car manufacturing and medicine technology. To meet these requirements, a real-time process control system has been developed which determines the welding quality through a locally resolved temperature profile. By analyzing the resulting weld plasma received data is used to verify the stability of the laser welding process. The determination of the temperature profile is done by the detection of the emitted electromagnetic radiation from the material in a range of 500 nm to 1100 nm. As detectors, special high dynamic range CMOS cameras are used. As the emissivity of titanium depends on the wavelength, the surface and the angle of radiation, measuring the temperature is a problem. To solve these a special pyrometer setting with two cameras is used. That enables the compensation of these effects by calculating the difference between the respective pixels on simultaneously recorded images. Two spectral regions with the same emissivity are detected. Therefore the degree of emission and surface effects are compensated and canceled out of the calculation. Using the spatially resolved temperature distribution the weld geometry can be determined and the laser process can be controlled. The active readjustment of parameters such as laser power, feed rate and inert gas injection increases the quality of the welding process and decreases the number of defective goods.

With the development of laser technology, higher requirement is presented on measurement technology of laser beam. The measurement technology of laser beam develops from the original Knife-edge method, Slit scanning method into the latter Shack-Hartmann method. The test index of laser beam also develops from originally testing power, wavelength into putting much value on the testing of wavefront, and characteristic value of a laser beam. In this paper, we go deep into study the method of measurement of laser beam and present a laser beam measurement method which is takes photos on focal plane to calculate the wavefront and the laser characterization. The difference between Shack-Hartmann method and this method is analyzed. The results of experiment show that, this method is simple apparatus, and high precision, and it will be a development tendency on the laser beam measurement field, in the future.

Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. The laser Assisted Friction Stir Welding (LAFSW) combines a Friction Stir Welding machine and a laser system. Laser power is used to preheat and to plasticize the volume of the workpiece ahead of the rotating tool; the workpiece is then joined in the same way as in the conventional FSW process. In this work an Ytterbium fiber laser with maximum power of 4 kW and a commercial FSW machine were coupled. Both FSW and LAFSW tests were conducted on 3 mm thick 5754H111 aluminum alloy plates in lap joint configuration with a constant tool rotation rate and with different feed rates. The two processes were compared and evaluated in terms of differences in the microstructure and in the micro-hardness profile.