High Power Carbon Dioxide Laser Research Articles

Microstructure and Hot Corrosion Properties of Laser Cladding of a Co-Base Alloy on the Leaf Surface of Gas Turbine

The temperatures inside the gas turbine reach up to 1000°C, alloys used for gas turbine components must be oxidation, and corrosion resistant, and stable in structure under high temperature circumstances. A Co-based alloy was cladded on the 1Cr18Ni9Ti stainless steel surface using a high power carbon dioxide laser. The microstructure evolution and hot corrosion properties of samples in 75%Na2SO4+25%NaCl saline were investigated. The results show that the microstructures of the cladded layer is fine, and the hot corrosion resistance of the cladded layer was significantly improved because of the formation of a protective oxide film of CoO and CoO•Cr2O3. Under high temperature corrosive atmosphere, the high content of Co promoted the formation of the protective oxide film. The refinement of dendritic structures and the formation of Co-based alloy oxides lower the penetration rate of the sulphur ions that induce the intergranular corrosion.

Laser Surface Strengthening on Module Steel

Whether laser surface strengthening on module steel can have an effect on intensity, shock resistance and wearing resistance. Through analysis of different materials with different laser methods, this paper uses high-power carbon dioxide lasers to process the work of strengthening laser on CrWMn, conduct structural analysis and test on laser hardening layer, through data and figure, demonstrate that primary structure of the matrix is obviously detailed after processing and the intensity is obviously strengthened. After laser surface melting on H13, we find that the surface flawless, smooth, even and fine, highly intense and non-corrosive.

Particle size analysis of material removed during CO2 laser scabbling of concrete for filtration design

This article examines the particles formed during optimized laser scabbling of concrete in order to help determine an effective filtration strategy for the process. The laser scabbling technique has been developed for noncontact removal of radioactive contaminated surface concrete layers. Surface layer removal is effected using a high power carbon dioxide laser beam to generate stresses in the substrate (caused by temperature gradients and dehydration) which break up the surface. The material removed will be contaminated with radionuclides and its efficient collection must be ensured to prevent the escape of radioactive contaminated particles. The filtration methods selected depend on the size of the particles produced and transport characteristics in an airflow. The particles removed were examined using a laser diffraction particle sizer (for particles below 80 μm physical diameter) and sieving (above 150 μm physical diameter) to determine the particle size distribution. Scanning electron microscope (SEM) analysis was used to identify the components present. The study found that particles removed were constituents of the parent concrete, there were no signs of melting and a small volume fraction (less than 1%) of sub-100 μm physical particle diameter. Particles with aerodynamic diameters under 100 μm are airborne and those between 1 and 30 μm are inhaled into the thoracic and bronchial tracts and lungs. Efficient filtration is required to capture these particles. However, filtration is difficult in the 0.1–1 μm aerodynamic diameter range, which comprises only 0.02% by volume of the removed material. It is considered that laser scabbling of concrete using this method will produce no additional risks than the use of other surface removal mechanisms.

Microstructure evolution of laser clad layers of W–C–Co alloy powders

Clad layers using high power carbon dioxide laser and various powder compositions of W, C, Co and WC on carbon steel substrate have been investigated. Microstructures of the clad layers are greatly affected by the processing parameters: powder size; powder type; shielding gas; degree of dilution; and geometry of the clad layer. Clad layers with large WC particles in a eutectic matrix and a high hardness, or with a mostly eutectic structure and low hardness, can be made for applications of cutting tools or wear resistant surfaces, respectively. Microstructure such as: (1) WC, Co 3W 3C, and a binary eutectic mixture of Co 3W 3C and α-(Fe,Co); (2) Co 3W 3C and a binary eutectic mixture of Co 3W 3C and α′-(Fe,Co); (3) a binary eutectic mixture of Co 3W 3C and α′-(Fe,Co) have been produced in the clad layer.

Recovery and viability of an acute myocardial infarct after transmyocardial laser revascularization

Objectives. The short- and long-term effectiveness of transmyocardial laser revascularization was evaluated in the setting of an acute myocardial infarction.Background. Theoretically, transmyocardial laser revascularization allows direct perfusion of the ischemic area as ventricular blood flows through the channels to the myocardium.Methods. Infarcts were created by coronary occlusion in 30 sheep. Eighteen of these sheep were studied to assess short-term efficacy. The infarct was reperfused after 1 h by either removing the occlusion or by laser drilling using a high power carbon dioxide laser. The occlusions were left in place for the control group. To monitor regional recovery, percent systolic shortening was measured. To evaluate long-term effectiveness, 12 additional sheep underwent creation of an infarct. Six were treated with the laser, and six were untreated. The animals were restudied 30 days later.Results. In the short-term experiment, the control and reperfusion groups exhibited no recovery of regional contractility. The laser group demonstrated improvement throughout the recovery period. There was a significant difference in the area of necrosis within the same area at risk (reperfusion group 44 ± 6% and control group 39 ± 5% vs. laser group 6 ± 2%). After 30 days, none of the control animals showed evidence of contraction in the infarct, whereas the laser-treated animals did. Histologic analysis of the laser-treated infarcts revealed patent channels surrounded by viable myocardium. The control-group infarcts were necrotic and scarred.Conclusions. On the basis of both short- and long-term improved contractility, as well as diminished necrosis in the area at risk, these results indicate that transmyocardial laser revascularization may be an alternative method of treating ischemic heart disease.

Truncated cone as a pseudoconjugator in a high-power carbon dioxide laser

The incorporation of a retroreflecting, pseudoconjugating cone as a folding element in a double-pass unstable resonator of a high-power carbon dioxide oscillator–amplifier is presented. The concept, when implemented with a truncated cone, has yielded significant improvements in optical energy extraction efficiency, beam quality, and alignment stability. The performance of such a modified clear aperture cone resonator, in comparison with a standard roof prism cavity geometry, is discussed.

Standard of Specular Reflectance at Glancing Incidence for the Infrared Region

The performance of high power carbon dioxide and free electron lasers depends upon the quality of mirrors used in them. A precise characterization of mirrors is required, and this is achieved by employing reference standards. Standards for the calibration of reflectance scale for the infrared region are not available. The present work describes the development of a specular reflectance standard at glancing angles of incidence from 10° to 70° for the 2,5 μm to 25 μm infrared region. Whereas aluminium and gold mirrors have been used as high reflectance value standards, single and double surface polished silicon and germanium have been employed as standards at low reflectance values.

The optical properties and laser irradiation of some common glasses

The reflectance spectra of four common glasses have been measured from 300 to 2000 cm-1. The glasses examined were Vitreosil, Tempax, Sodalime, and BK7. A Kramers-Kronig analysis of the reflectance data was used to calculate the real and imaginary parts of the refractive index. These were used to predict how the glasses would react to high-power carbon dioxide laser irradiation. The results indicated that the lower optical absorption coefficient and the lower thermal expansion coefficient of the Vitreosil glass should make it less susceptible to laser induced damage.

Deformations induced by laser welding in nuclear components

One of the advantages of the application of deep penetration (10–15 mm) laser welding on stainless steel is the reduced deformation induced in the workpiece. This characteristic is of particular importance when welding components subjected to stringent dimensional requirements. This study refers to welding with high power (15 kW) carbon dioxide laser on mock-ups of the components of the sommier of fast reactor nuclear power plants. The deformations measured on the mock-up can be interpreted in the light of the particular geometry of the welded joint studied in order to minimise these effects.

The topography of laser-irradiated germanium

Considerable interest centres around the use of germanium as a reflector material in high-power carbon-dioxide lasers. An important problem is the damage caused to the mirror surface as the result of the dynamic development of imperfections. This damage may be caused by an interference process which has been described previously. A characteristic of the damage which occurs is the melting of the germanium followed by resolidification. The authors describe a certain type of melting pattern which depends upon density differences between the liquid and solid phases. The experimental phenomenon is first described with reference to germanium laser mirror damage and this is followed by a theoretical model of the resolidification of molten regions where a density difference occurs between the solid and liquid phases, as in paraffin wax for example.

Strengthening of halides for infrared windows

The alkali halides are promising candidates for high-power carbon dioxide laser windows. However, their poor mechanical properties limit their application for windows. In this paper, several methods of strengthening these materials will be discussed. These methods include impurity addition, solid solution formation, use of systems with solid-solid immiscibility gaps and polycrystalline formation. Characterization will include both optical and mechanical properties. The studies indicate that solid solutions (KCl-KBr) can strengthen the halides about twofold without affecting optical properties. An eight-fold increase in hardness has been produced using the NaCl-KCl system but the optical properties are adversely affected. The results of impurity addition (CaCl2) in KC1 are not clear, but the method does not look promising. Results of polycrystalline formation will also be discussed.

High power lasers

Although Mr P D Lomer's article on 'High power carbon dioxide lasers' was informative (Physics Bulletin January 1972 p19), I should like to correct the impression given that peak powers of CO2 lasers in the pulsed mode have reached levels comparable to those of solid state lasers. The highest figure quoted in the article was 130 J, and taking this energy to be contained in a 60 ns pulse (full width at half intensity) the highest power attained by a CO2 laser is about 2 GW.