Laser welding of AISI 904 L super austenitic stainless steel using a diffusion cooled slab 3.5kW CO2 laser and employing two different shielding gases, namely argon and helium, was carried out. The ...laser weld bead profile depends on various parameters such as beam power (BP), travel speed (TS) and focal position (FP) of the laser spot. These parameters have to be selected suitably to obtain the desirable output. The cross sectioned area of the bead profiles measured using an optical microscope to determine the bead width and depth of penetration. X-ray diffraction used for phase identification confirmed that the weld structure was fully austenitic and dendritic. Hardness was observed to increase in the weld bead with respect to the parent metal and it was related to the microstructural refinement induced by a rapid cooling of the weld zone.
Laser triggering is interesting for gap switches used in power systems and pulsed power because of its well-controllable delay and jitter time, as well as its electrically uncoupled characteristics. ...Despite the large attention that was paid to various parameters affect triggering characteristics, the underlying physics of laser triggering remain unclear. In this paper, the nanosecond-laser-triggered pulsed discharge was investigated in atmospheric air. Using a picosecond laser, a high-time-resolution interferometer was constructed and the laser- and discharge-produced plasmas were detected. The shockwaves formed by instantaneous release of the laser and electrical energy into the ambient air were well distinguished. Using the interferograms, phase-shift maps were extracted by a 2-D fast Fourier transform method. Finally, preliminary experiments were performed on laser-triggered discharge from a prototype gap switch, and delay and jitter results were given.
The fracture toughness (K1C) of Si3N4 and ZrO2 engineering ceramics was investigated following CO2 and fibre laser surface treatment. Near surface modifications in the hardness were investigated ...using Vickers indentation. Crack lengths and the crack geometry were then measured by optical microscopy. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Computational and analytical methods were used to determine the K1C. An increase in the K1C of both ceramics was found after CO2 and fibre laser surface treatment compared to the as-received surfaces. The K1C of the CO2 laser radiated surface of the Si3N4 was > 3% higher compared to that of the fibre laser treated surface. This was due to softening of the near surface layer of the Si3N4 which lowered the hardness, and in turn increased the crack resistance. The effects were not similar in ZrO2 as the fibre laser radiation produced an increase of 34% compared to that of the CO2 laser radiation. This was due to propagation of lower cracks resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the final K1C through an induced compressive stress layer. The K1C modification of the two ceramics treated by the CO2 and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption coefficient, the beam delivery system and the differences in the brightness of the two lasers used.
Low-power laser forming by raster scanning is a promising technology for shaping thin sheets in a non-contact manner, using a laser beam scanned over the surface. In this work, the change of material ...microstructure and the related corrosion behavior are investigated in the context of local temperature evolution during the scanning action. Graphite coated AISI 302 stainless steel coupons have been bent to different angles using a 60
W CO
2 laser and the resulting cyclic polarization behavior in sulfuric acid was measured. The so revealed sensitization of the material is discussed on the basis of microstructural changes caused by temperature-induced phase transformations. The total times of permanence at temperatures favoring specific transformations were obtained by numerical simulation of the process. It was found that even when no surface melting takes place the recurrent rise of temperature within the material is sufficient to sensitize the non-irradiated side. This effect might be a limiting factor in applications of laser formed AISI 302 in corrosive environments.
A plasma column generated in the PF-1000 device working in deuterium gas at a current level of 1 MA was investigated with interferometric diagnostics and scintillation detectors. The beam of ...diagnostic laser of 527-nm wavelength was optically split into 16 beams with a time delay in the range from 0 to 220 ns. This diagnostic tool makes possible the imaging of the evolution of pinch geometry, the axial and radial distributions of plasma density in the column at the stagnation phase, and their comparison with the evolution of X-ray and neutron production. The evolution of dense structure is described with respect to its importance for fusion processes.
We have tested whether a recent model Appl. Phys. Lett.95, 174105 (2009)APPLAB0003-695110.1063/1.3254236 that considers the angular dependence of laser-ablation rates, including reflection losses and ...geometrical dependence of incident fluence, and the effect of plume absorption can have significant effects for refractive surgery patients. We have developed a mathematical procedure and deduced equations that show that this model can significantly influence postsurgical corneal parameters (radius and asphericity) and, thus, should be considered in ablation algorithms in order to achieve a better emmetropization and an effective correction of eye aberrations.
Experimental measurements and analysis of pulsed 1064-nm Nd:YAG laser-induced air breakdown plasma at 760 torr has been carried out using high-speed and high-resolution laser shadowgraphy and optical ...diagnostics. Three different experimental laser energies and pulsewidths such as 170 mJ at 8 ns, 130 mJ at 7 ns, and 65 mJ at 12 ns are studied. The laser pulses were focused down to a ~ 7-μm spot size in air and the resulting laser flux densities range from 4 to 14 TW/cm 2 . A 532-nm laser shadowgraphy coupled with high-speed and high-resolution image capturing diagnostics has been established to investigate spatiotemporal evolution and hydrodynamic behavior of the 1064-nm laser-induced plasma and neutral-density shock during the formation, expansion, and collapsing stages. The observed plasma formations were aspherical due to absorption translation during the initial laser-energy coupling. The aspherical feature seeded the hydrodynamic instability leading to the ultimate destabilization of the hot gaseous core after approximately 10 μs. The active plasma lifetime through plasma self-luminescence measurements indicate variations from 200 to 500 ns for the three laser pulses. Shock propagation velocity and plasma volume for three laser pulse series indicate similarly shaped profiles at different expansion velocities. Early plasma expansion velocities of 20 km/s were measured, and using Hugoniot relations, the neutral shock pressures and temperatures were inferred, and the results at the early plasma expansion stage were found to be over 1000 atm and 4 eV.
We report on the operation and beam profile analysis of an optically pumped GaSb-based vertical-external-cavity surface-emitting laser at 2.33 μm. To compensate for the low thermal conductivity of ...the laser chip, an intracavity heat spreader made from polycrystalline chemical vapor deposition diamond was bonded to the top surface of the chip. In this configuration, at -18/spl deg/C, a maximum continuous-wave output power of 0.6 W in a multitransverse mode beam (M 2 /spl ap/2.7) was achieved, limited by the available pump power. Optimizing the resonator for TEM/sub 00/ laser emission (M 2 /spl ap/1.1), an output power exceeding 0.4 W was observed at the same temperature.
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