Although material processing with high power lasers has found widespread use in a variety of industries such as the automotive industry, electrical and electronics industries, aerospace industry etc., civil engineering construction is one field that has lagged behind in the use of lasers for material processing. This is in spite of the fact that a large variety of materials including ceramics, metals and plastics are used in very large quantities for civil engineering construction. The main reasons for the delay in the adopting of laser for processing construction material seem to be the high costs involved and the lack of sufficient power for processing heavy and thick materials. However, with the advent of more compact lasers with higher powers, higher efficiencies and lower photon costs, greater interest has been shown in recent years in the possible uses of high power lasers for material processing in the construction industry. The author traces some of the past work carried out both in Japan and abroad on the use of lasers in civil engineering, specially with respect to the processing of inorganic material such as concrete, natural stones, tiles and rocks. Recent developments regarding laser decontamination and laser assisted rock excavation are also introduced.
In Europe especially in Germany there is a growing demand for redevelopment of concrete apartment buildings. For giving the apartments a new outline, concrete walls have to be removed and openings for new doors have to be made. The construction industry was searching for a cutting technology without using water and without loud noise for avoiding the temporal relocation of residents. At Fraunhofer-Institut IWS a laser cutting technology which fulfills these conditions was developed. Using a 3 kW-Nd-YAG-laser we succeeded in cutting 70 mm concrete with up to 25 mm/min. The technology is described and the design of a cutting equipment suitable on building sites is presented.
Rock excavation experiment with a 10kW-class CO2 laser was demonstrated as a basic study for field application of high power lasers. Sample rocks used in this experiment as a workpiece were tuff breccia and granite. Effect of assist gases on the excavation rate was surveyed. Oxygen, nitrogen, and air were examined and found not to be useful. It was because the gas flow could not blow the molten rocks off, but only helps to cool in case the hole races certain depth. Excavation rate on both rocks for a various output powers was measured to determine thermal constants inherent to each rock. It was found that the excavation rate resulted in slower, as the hole becomes deeper, because of the deterioration in evacuation efficiency of the molten rock. Thermal parameters of the both rocks were derived from the experimental results. Using simplified thermal balance model, it was estimated that a 50 kW-class mobile laser system has a potential to outperform the conventional mechanical excavation technique.
In order to excavate rock bed without reaction, the CO2 laser was utilized. Feasibility of using laser energy to excavate rock was evaluated. Two kinds of rock were subjected to CO2 laser beam preliminary experiment. The cross section of rock samples subjected to CO2 laser was observed carefully along the depth from the irradiated surface.
A new construction method by laser excavation is studied. First, the fundamental experiments were conducted for investigating the interaction between rocks and laser.s Next, some parts of lasers were improved. Two beams generated by the YAG laser system are coupled to gain the 6kw beam. This is applied through a long focus lens on the rock excavated from the similar place in which the large- scale rock failure occurred. 10-minute irradiation produced a small hole of 230mm depth and 20mm in diameter. The same experiment is achieved out of doors to demonstrate laser boring has a practical use.
More than 30 years have already passed since the first commercial nuclear power plant in Japan was put in operation. Presently, about 50 commercial nuclear power plants (NPPs) are operating and in the future NPP will be ceased the operation and the plant will be decommissioned. NUPEC has been developing the decommissioning technology undertaking the safe, secure, and rational decommissioning for NPPs since 1982. NUPEC has focused its development effort on techniques for decontamination before dismantling, reactor facility dismantling, measurement of residual radioactivity in buildings, waste decontamination, recycling.
In the research and development of various advanced technologies needed for decontamination and decommissioning of nuclear facilities, laser was applied to decontamination of metal and concrete surfaces and to cutting of large metal of low level radioactive waste. (a) Laser decontamination for metal waste: Metal waste was irradiated by laser in the atmosphere of chloride gas, and contaminant was changed from oxide to chloride which is sublimable or soluble in water and could be easily removed; and also metal waste coated with gel-decontamination reagent was irradiated by laser, and contaminant could be removed through the laser-induced chemical reaction. (b) Laser decontamination for concrete surface: Concrete surface was bursted or vitrified by laser irradiation and easily removed. (c) Laser cutting: Laser cutter was applied to cutting of large metal wastes such as tanks arising from dismantling of nuclear facilities.
We investigated the mixing of simulated surface contamination in the cut surfaces of laser-cut stainless steel. A 10 micrometers layer of molybdenum was coated by wire explosion spraying of 8mm-thick 304L stainless steel to serve as the simulated contaminated metal plate. The cutting was done with a CO2 laser using a nitrogen and oxygen gas mixture as cutting assist gas. The mixing of the molybdenum into the cut walls was evaluated by EPMA surface analysis and fluorescent x-ray analysis. The result revealed that the degree to which the molybdenum was mixed into the cut surfaces decreased as the concentration of oxygen in the assist gas increased. Also, the result of contaminant removal from the cut piece by chemical oxidation reduction decontamination processing was that the greater the oxidation, the less the molybdenum that remained after the processing. Thus, to reduce the mixing of simulated surface contaminants in the cut surfaces, a cutting assist gas that has a high concentration of oxygen should be used.
A justification of laser decommissioning of nuclear reactor of Kursk Nuclear Power Plant. The main reason of laser beam application in this case is the marked decrease of radioactive radiation exposure of the service personnel. The use of a high power laser beam provided to realize laser cutting and welding processes of a distance up to 35m between the laser and the workstation placed behind a contre-radiation shield. By application of laser cutting gas and dust contamination is tenfold decreased. Some result of decommissioning application of a stationary laser workstation based upon a 5kw fast-transverse-flow discharge CW-CO2 laser TL-5M installed of a nuclear reactor site are presented. A special high-beam-quality model of the laser was developed to satisfy the needs of decommissioning. Laser cutting process was applied to decommissioning of fuel channels of RBMK-1000 reactor, after their extraction from the reactor active zone during the procedure of channels replacement.
Laser technology has much possibility to accomplish nuclear facility decommissioning effective and the laser application to cutting technique and decontamination technique is considered in Japan. Nuclear Power Engineering Corporation had developed CO laser for cutting technique, and had developed YAG laser for decontamination.
Investigations on laser cleaning for decontaminated surface have been performed by simulations and experiments. Basic equations of simulations are the equation of thermal conduction, the absorption of laser energy, boundary conditions of melting and evaporation. Simulations have bee performed for the case of 2-layers, basic material is SUS304 and surface pollutant is Fe3O4. Simulation results were in good agreements with experiments at the wide range of laser fluence.
The chemical oxygen-iodine laser (COIL) is a high power, fiber deliverable tool, which can be used for a number of different industrial applications. COIL is of particular interest because of its short fiber deliverable wavelength, high scaleable continuous wave power, and excellent material interaction properties. In past research the University of Illinois at Urbana-Champaign identified and decommissioning and decontamination (DD) of nuclear facilities as a primary focus for COIL technology. DD will be a major challenge in the coming decades. The use of a robotically driven fiber delivered cutting/ablation tool in contaminated areas promises to lower risks to workers for the DD mission. Further, the high cutting speed of COIL will significantly reduce the time required to cut contaminated equipment, reducing costs. The high power of COIL will permit the dismantling of thick stacks of piping and equipment as well as reactor vessels. COIL is very promising for the removal of material from contaminated surfaces, perhaps to depths thicker than an inch. Laser cutting and ablation minimizes dust and fumes, which reduces the required number of high efficiency particulate accumulator filters, thus reducing costly waste disposal. Other potential industrial applications for COIL are shipbuilding, automotive manufacturing, heavy machinery manufacturing, tasks requiring underwater cutting or welding, and there appear to be very promising applications for high powers lasers in the oil industry.
By using a fiber-transmitted laser beam and high pressure oxygen gas, underwater laser cutting of thick stainless steel was demonstrated. In the field of decommissioning, underwater cutting of nuclear facilities is desirable. For this operation, it is very useful to apply the laser beam transmitted through optical fiber because of flexibility. We used chemical oxygen-iodine laser for fundamental experiments with laser beam power of 1-7kW. And for this experiments, we designed cutting heads with some ideas for nozzles and optics. The nozzles have various nozzle diameters and two kinds of shapes; one is conical, and the other is divergent. The latter was designed to make a supersonic gas flow by using high pressure oxygen gas. And we prepared several focusing optics with different focal lengths, which have influence on both the focal spot diameter and the depth of focus of the laser beam that incidents upon a workpiece. Cutting ability was measured by cutting a tapered workpiece. From this investigation it was clear that the nozzle-to-workpiece distance that was about 10mm had the large tolerance of deviation, and there was a suitable optics according to laser power.
Conceptual designs of a chemical oxygen-iodine laser (COIL) facility for decommissioning and dismantlement (DD) of nuclear facility is proposed. The requisite output power and beam quality was determined base don our preliminary experiments of nonmetal material processing. Assuming the laser power of 30kW, it is derived that the beam quality of M2 equals 36 required to cut a biological shield wall of a nuclear power plant at a cutting speed of 10mm/min. Then the requisite specification of an optical fiber to deliver the laser is calculated. It turned to be quite extreme, core diameter of 1.7mm and NA equals 0.018. The mass flow and heat balance of proposed facility is calculated based on our recent COIL studies. With the high-pressure subsonic mode, the vacuum pump size is minimized compared to the supersonic operation. Finally, the size of the facility is estimated assuming tow-hour continuous operation. It is revealed that such a system can be packed in five railway containers.
The Chemical Oxygen-Iodine Laser (COIL) has been developed at the Air Force Research Laboratory for military applications. For example, the COIL is to be use as the laser device for the ABL. A high power laser is useful for applications that require the delivery of a substantial amount of energy to a very small focused laser spot. The COIL is a member of the class of high power lasers that are also useful for industrial applications, including the materials processing task of high speed cutting and drilling. COIL technology has received considerable interest over the last several years due to its short, fiber- deliverable wavelength, scalability to very high powers, and demonstrated nearly diffraction-limited optical quality. These unique abilities make it an ideal candidate for nuclear reactor decommissioning and nuclear warhead dismantlement. Japanese researchers envision using a COIL for disaster cleanup and survivor rescue. It is also being studied by the oil and gas industry for well drilling. Any commercial or industrial application that requires very rapid, precise, and noninvasive cutting or drilling, could be readily accomplished with a COIL. Because of the substantial power levels available with a COIL, the laser could also be used for broad area applications such as paint stripping. This paper includes a collection of experiments accomplished at the Air Force Research Laboratory Chemical Laser Facility, including metal cutting, hole drilling, high power fiber optic transmission, and rock crushing.
A development of a three-color solid-state laser on phosphate neodymium glass for pulse holography is offered in the present paper. The laser has been assembled under the multicascade scheme with a single master oscillator. The powerful IR radiation on an output of such system has been frequency converted into green, dark blue and red radiation due to processes of the second harmonic and third harmonic generation of a neodymium laser radiation and generation of first anti-Stokes component of the Stimulated Raman scattering respectively and has been divide into three various bema of different color. Varying the conditions of realization of above processes, it is possible to redistribute the radiation energy of the system between beams of various colors over a wide range. The energy of each beam will be sufficient for exposition of a photomaterial of the appropriate spectral sensitivity, and the joint influence of beams will make possible to obtain color pulse holograms and, in particular, color holographic portraits.
A chemical oxygen-iodine laser (COIL) was used for cutting aluminum, titanium, inconel and copper plates. The laser was operated with a stable resonator having an intracavity aperture to produce a circular COIL beam with very few transverse modes. The multimode focal spot diameter was calculated to be 0.24 mm. The new aluminum cut was of particularly high kerf edge quality. These COIL cutting data are compared with an existing theoretical laser cutting model. Using thermophysical data for aluminum, titanium,l inconel and copper, this theory agrees very well with the data. To test the versatility of the model, the effects of different assumptions are examined; different assumptions produced very little effect on model predictions at high cutting speeds and a small difference at very slow cutting speeds. Overall, the theoretical model provides good agreement with experiments for a wide variety of metals.
The COIL has drawn considerable attention owing to its short, fiber-deliverable wavelength, scalability to very high powers, and nearly diffraction-limited optical quality. These unique abilities make it an ideal candidate for rapid cutting of thick metals and other laser materials processing applications. Cutting experiments have been conducted at the Air Force Research Laboratory Chemical Laser Facility for a number of metals including stainless steel, nickel, copper, titanium and aluminum. A simple model for the cutting performance has been very successful in predicting the cutting sped and depth for most of these materials. Different assumptions of this model produce very little effect on the model predictions at high cutting speeds an a small difference at very slow cutting speeds. Additional physical effects such as the effects of vaporization, which can be significant at slow cutting speeds when cutting very thick sections, is incorporated into the model. This paper demonstrates how various assumptions within the derivation of the model can lead to different forms of the scaling law.
Laser shot peening, a surface treatment for metals, is known to induce residual compressive stresses to depths over 1 mm providing improved component resistance to various forms of failure. Recent information also suggests that thermal relaxation of the laser induced stress is significantly less than that experienced by other forms of surface stressing that involve significantly higher levels of cold work. We have developed a unique solid state laser technology employing Nd:glass amplifier slabs and SBS phase conjugation that enables this process to move into high throughput production processing.
Parapets in buildings are complex in shape and are subject to strains and deformation caused by temperature changes and other factors. At the same time, high durability and god appearance are essential requirements of parapets. In this study, the application of the YAG laser for welding thin stainless steel sheets for use as parapet in buildings was studied using both austenitic and ferritic stainless steels. It was found that high speed welding at speeds of 1000nm/min was possible for both types of stainless steels. Welding was minimized by the use of pulsed power. In addition, discoloration of the weld could be prevented. These characteristics facilitate the subsequent painting process of the welded components. Also, it was found that laser welding offers the advantage that there is no limitation in the design of curved parts.
This contribution presents, as a first result of thorough investigations concerning the effect of laser irradiation on wood, the laser cleaning applied in restoration and conservation of 600 years old wooden panels in an historically important building at Pirna. They were uncovered during archaeological examinations in 1994. In one room of that building the work of restoration revealed fully preserved wooden panels on walls and ceiling. Most panels on the walls are severely damaged and converged with multiple paint layer. Aim of the work is to remove the multiple paint laser from the severely damaged wooden panels. Conventional cleaning test showed that one of the methods known to restorers met the requirements. Therefore laser cleaning was tried. Investigations, like thermal measurements and SEM- images show that there is no damage due to laser cleaning. The ablation rate of laser cleaning depends on grade of decay and on thickness of paint layers. This presentation shows that ablation with short pulsed Nd:YAG-laser could be a new method for restoration of damaged wood surfaces.
In buildings that are old it becomes difficult to identify the types of woods used when planning their repair. This is because of blackening of the tree resin and discoloration due to the adhesion of the dust. Unless the wood can be identified correctly, parts cannot be replaced because differences in the expansion coefficient and water absorption can lead to dimensional instability. Furthermore, in the case of historically important buildings, it is not possible to cut out large-sized samples for laboratory identification. This paper explains a method developed to identify woods from 3 X 3 X 0.5 mm samples by measuring the distribution of the vessels of woods by a He- Ne laser. A database of identification parameters of more than 30 kinds of woods was made allowing identification and properties of most woods including imported woods used in architecture. The method developed is more accurate than the conventional identification methods used up to now. It was applied to identify the woods used in 100 to 400 year old buildings and to formulate their repair specifications. The method has also been applied to assess the suitability of imported woods for use in modern high buildings.
Environmental disruption by lumber cutting is an ever- present problem in the modern world. Bamboo is a fast growing tree which, even if it is cut every 3 years, grows for its subterranean stem naturally. Thus, the use bamboo- based materials can be regarded as environmentally friendly, and this paper deals with the use of bamboo as flooring material for buildings. Since mechanical cutting of bamboo for making flooring gives rise to problems such as difficulty in cutting perpendicular to the bamboo fiber direction, wear of the cutting tool and generation of dust etc., a study on laser processing of bamboo flooring was carried out. The laser cutting conditions were investigated and optimized. It was shown that laser cutting can offer many advantages.
Some possibilities of laser processing of natural stones were evaluated and the laser irradiation parameters suited for the following materials removal and melting processes were examined. 1) Surface roughening of granite, 2) Cutting of marble after water immersion, 3) Drilling of holes in natural stones for locating metal fittings, and 4) Surface melting and glazing of soft stones.
As for building, a dimension varies in the design greatly. High dimension precision is required of the large tile of 6 X 900 X 1800 mm, and it is important to correspond to the local dimension. So it was carried out that eh CO2 laser of 2kW was used for cutting of the large tile.
Painted metal exteriors of buildings begin to degrade in about 10 years due to solar heat, UV rays, the sea salt adhesion, the acid rain etc. When degradation and exfoliation of the paint film occurs, rust appears in the metal and replacement or repainting becomes necessary. The adhesion of paints on metal is usually achieved by chemical adhesion or by increasing the surface area by blast processing. In this study, the possibility of improving paint adhesion by forming minute holes on the metal surface by laser irradiation was studied through modeling of the adhesion of the paint film and adaptability to deformation. The viscosity and painting method depend on the size and location of the oles. The presence of the holes makes it possible to form complicated shapes by pressing because the holes absorb some of the strain caused by pressing.
Curved micro-tunneling using small conduit pipes with diameters of 1m or less is recently applied in many construction sites. We have come up with a new position sensing system to pinpoint the head of the first pipe even when it cannot be seen directly from the base position. It differs from the traditional method of using the collimated laser beam, in that a diode laser with a large divergence is used as the point source of light. The direction of the point source of light is detected by using an objective lens and CCD camera. To apply this method to the position detection of the first pipe, the structure of the sensing unit and its detection accuracy were examined and the following result were obtained. (1) The structure using a polarized beam splitter can suppress error led by rotating the sensing unit. (2) Through simulation and some field test, 20 seconds or less detection accuracy of direction angle was achieved.
The grooves on the floor to allow sliding of automatic doors in office buildings, hospitals, etc., can cause inconvenience or even accidents because the wheels of wheel chairs or high-heeled shoes can get stuck within the grooves. In addition, collection of rainwater and dust within the grooves impede the proper functioning of the automatic doors. As a counter measure to this problem, a caterpillar-like retractable groove cover was designed and made from stainless steel. Since the edges of the cover required high precision, high speed laser processing was applied in the making of its component parts. The caterpillar cover design, laser processing conditions, durability testing by repetition of door opening/closing etc. are explained in this paper. The covers developed through this study were installed in the automatic doors of a high rise building and have been found to be effective in overcoming the problems mentioned above.
Surface removal technologies are being challenged from environmental and economic perspectives. This paper is concerned with laser ablation applied to large surface cleaning with an automatized excimer laser unit. The study focused on metallic surfaces that are oxidized and are representative of contaminated surfaces with radionuclides in a context of nuclear power plant maintenance. The whole system is described: laser, beam deliver, particle collection cell, real time control of cleaning processes. Results concerning surface laser interaction and substrate modifications are presented.
High power Nd:YAG laser beam with wavelength 1064nm, pulsewidth 10 picosecond regime was focused onto the scanning targets of SUS304 stainless steel with Zn coating of thickness 21 micrometers , and delivered via a step index fused silica optical fiber of length 3m and core diameter 1mm. Irradiation ablation effect and some basic aspects of high power laser beam transporting in optical fiber were studied. Ablation rate was defined as ablated volume to laser fluence and used as a description of ablation cleaning ability which was investigated by means of ablated profile measurement, ablation rate calculation, chemical composition analysis of ablated area.
The boring process of various materials with KrF excimer laser was investigated by measurements of the penetration time. The parameters in this experiment were the frequency of the laser operation and the distance of the target from the laser focal point. The correlations between the penetration time and material properties such as density, thermal conductivity, coefficient of the thermal expansion, specific heat, Young's modulus and Poisson's ratio were obtained from this experiment. The penetration time was proportional to the logarithmic of the specific heat and that of the Young's modulus. Generally the target put at the focal point of the laser was penetrated most rapidly. But in the case of the quartz plate, the most rapidly penetrated point was quite in front of the laser focal point in spite of its less beam intensity.
The inside defect in carbon steel with the diameter of 100 micrometers was successfully detected by a laser ultrasonics technique. Irradiation of a Q-switched Nd:YAG laser was used for ultrasonic degeneration, and a frequency doubled CW Nd:YAG laser combined with a Fabry-Perot etalon were used for detection of ultrasonic vibration on the specimen surface. The ratio of the inside defect diameter to the ultrasonic wavelength was estimated to be approximately 0.067. We also measured the dependence of the amplitude ratios of the first defect signa and the second longitudinal wave to the first longitudinal wave on the defect diameter.
Many types of CO2 lasers have been commercially available for processing not only of metals but also of non- metals such as acrylic, epoxy glass, ceramics, and glass due to the demands of industrial applications. CO2 lasers with a middle power range of approximately 200 W are attractively suitable for plastics materials processings because of the high absorption. Single-stroke drawing with focused beams has been generally used as a conventional method which requires high accuracy of processing. For sophisticated laser sculptures, various surface effects would be required which might be difficult to be realized only with the focused single-stroke drawing.
There is a growing interest in the laser radioactive decontamination of metal surfaces. It offers advantages over conventional methods: improved safety, reduction of secondary waste, reduced waste volume, acceptable cost. A main mechanism of cleaning in by lasers is ablation. In this work a pulsed TEA CO2 laser was used for surface cleaning, primarily in order to demonstrate that the ablation from metal surfaces with this laser is possible even with relatively low pulse energies, and secondary, that it could be competitive with other lasers because of much higher energy efficiencies. The laser pulse contains two parts, one strong and shot peak at the beginning, followed with a tail. The beam was focused onto a contaminated surface with a KBr lens. The surface was contaminated with 137Cs. Three different metals were used: stainless steel, copper and aluminum. The evaporated material was pumped out in air atmosphere and transferred to a filter. Presence of the activity on the filter was proved by a germanium detector-multichannel analyzer. Activity levels were measured by a GM counter. Calculated decontamination factors as well as collection factors have shown that ablation takes place with relatively high efficiency of decontamination. This investigation suggests that decontamination using the CO2 laser should be seriously considered.
Super high power laser systems have been pursued for the nuclear fusion research in these 30 years. GEKKO XII glass laser, LEKKO VIII CO2 laser, diode pumped solid state laser and PW cps Nd glass laser are developed at Osaka University. THey have proved to be very effective to the laser fusion research and also to the various applications in the wide field s of science and technology.
I treasure the analogy between aging and climbing a mountain. Ofcourse there are differences, mountain climbing is usually voluntary. As you climb a mountain you lose the ground detail but on a clear day broad views ofthe landscape are visible. The view from the mountain top is sometimes helpful to those working on the ground. I hope that the broad view ofthe technological landscape I present today will be ofsome use to those ofyou still lucky enough to be tilling that landscape. I will refer primarily to the I JS scene hut I believe that the technological landscape is as universal as human nature
The features of modern, high-power semiconductor diode laser arrays as sources for pumping high power solid states lasers are reviewed. The status and prospects for high power, high- beam quality Nd:YAG and Yb:YAG DPSSLs are examined. Developing concepts for novel high power DPSSLs are also outlined.