149 research outputs found
Wettability characteristics of carbon steel modified with CO2, Nd:YAG, Excimer and high power diode lasers
Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of a
common mild steel (EN8) was found to effect changes in the wettability characteristics of the steel,
namely changes in the measured contact angle. These modifications are related to changes in the surface
roughness, changes in the surface oxygen content and changes in the surface energy of the mild steel. The
wettability characteristics of the selected mild steel could be controlled and/or modified by laser surface
treatment. A correlation between the change of the wetting properties of the mild steel and the laser
wavelength was found
Contrasting the beam interaction characteristics of selected lasers with a partially stabilised zirconia (PSZ) bio-ceramic
Differences in the beam interaction characteristics of a CO2 laser, a Nd:YAG laser, a high power diode laser (HPDL) and an excimer laser with a partially stabilised zirconia (PSZ) bio-ceramic have been studied. A derivative of Beer-Lambert’s law was applied and the laser beam absorption lengths of the four lasers were calculated as 33.55 x 10-3 cm for the CO2 laser, 18.22 x 10-3 cm for the Nd:YAG laser, 17.17 x 10-3 cm for the HPDL and 8.41 x 10-6 cm for the excimer laser. It was determined graphically that the fluence threshold values at which significant material removal was effected by the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were 52 J/cm2, 97 J/cm2, 115 J/cm2 and 0.48 J/cm2 respectively. The thermal loading value for the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were calculated as being 1.55 kJ/cm3, 5.32 kJ/cm3, 6.69 kJ/cm3 and 57.04 kJ/cm3 respectively
Helium bubble formation in ultrafine and nanocrystalline tungsten under different extreme conditions
We have investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. At energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. We discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formatio
Wettability characteristics of an Al2O3/SiO2-based ceramic modified with CO2, Nd:YAG, excimer and high-power diode lasers
Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the
surface of an Al2O3/SiO2 based ceramic was found to effect significant changes in the
wettability characteristics of the material. It was observed that interaction with CO2, Nd:YAG
and HPDL radiation reduced the enamel contact angle from 1180 to 310, 340 and 330
respectively. In contrast, interaction with excimer laser radiation resulted an increase in the
contact angle to 1210. Such changes were identified as being due to: (i) the melting and partial
vitrification of the Al2O3/SiO2 based ceramic surface as a result of interaction with CO2,
Nd:YAG HPDL radiation. (ii) the surface roughness of the Al2O3/SiO2 based ceramic
increasing after interaction with excimer laser radiation. (iii) the surface oxygen content of the
Al2O3/SiO2 based ceramic increasing after interaction with CO2, Nd:YAG and HPDL radiation.
The work has shown that the wettability characteristics of the Al2O3/SiO2 based ceramic could
be controlled and/or modified with laser surface treatment. In particular, whether the laser
radiation had the propensity to cause surface melting. However, a wavelength dependance of
the change of the wetting properties could not be deduced from the findings of this work
Thermal Evolution of the Proton Irradiated Structure in Tungsten–5 wt% Tantalum
We have monitored the thermal evolution of the proton irradiated structure of W–5 wt% Ta alloy by in-situ annealing in a transmission electron microscope at fusion reactor temperatures of 500–1300 °C. The interstitial-type a/2 dislocation loops emit self-interstitial atoms and glide to the free sample surface during the early stages of annealing. The resultant vacancy excess in the matrix originates vacancy-type a/2 dislocation loops that grow by loop and vacancy absorption in the temperature range of 600–900 °C. Voids form at 1000 °C, by either vacancy absorption or loop collapse, and grow progressively up to 1300 °C. Tantalum delays void formation by a vacancy-solute trapping mechanism
Graphene Mode-Locked Ultrafast Laser
Graphene is at the center of a significant research effort. Near-ballistic
transport at room temperature and high mobility make it a potential material
for nanoelectronics. Its electronic and mechanical properties are also ideal
for micro and nanomechanical systems, thin-film transistors and transparent and
conductive composites and electrodes. Here we exploit the optoelectronic
properties of graphene to realize an ultrafast laser. A graphene-polymer
composite is fabricated using wet-chemistry techniques. Pauli blocking
following intense illumination results in saturable absorption, independent of
wavelength. This is used to passively mode-lock an Erbium-doped fibre laser
working at 1559nm, with a 5.24nm spectral bandwidth and ~460fs pulse duration,
paving the way to graphene-based photonics
Vorteile guter Fokussierbarkeit – Der Scheibenlaser erweitert das Anwendungsspektrum lampengepumpter Festkörperlaser
Debt and development of less developed countries
Typescript (photocopy).Digitized by Kansas Correctional Industrie
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