Search results for "laser beam"
showing 10 items of 141 documents
Aluminum to titanium laser welding-brazing in V-shaped grooveI
2017
International audience; Laser assisted joining of AA5754 aluminum alloy to T40 titanium with use of Al-Si filler wires was carried out. Continuous Yb:YAG laser beam was shaped into double spot tandem and defocalized to cover larger interaction zone in V shaped groove. Experimental design method was applied to study the influence of operational parameters on the tensile properties of the joints. Microstructure examination and fractography study were carried out to understand the relation between local phase content and fracture mode.Within defined window of operational parameters, statistically important factors that influenced the strength of T40 to AA5754 joints in V groove configuration w…
Diode laser welding of ABS: Experiments and process modeling
2009
International audience; The laser beam weldability of acrylonitrile/butadiene/styrene (ABS) plates is determined by combining both experimental and theoretical aspects. In modeling the process, an optical model is used to determine how the laser beam is attenuated by the first material and to obtain the laser beam profile at the interface. Using this information as the input data to a thermal model, the evolution of the temperature field within the two components can be estimated. The thermal model is based on the first principles of heat transfer and utilizes the temperature variation laws of material properties. Corroborating the numerical results with the experimental results, some impor…
A Simple Apparatus for the Determination of the Optical Constants and the Thickness of Absorbing Thin Films
2001
We report on a simple and inexpensive apparatus useful for measuring the optical constants n, k and the thickness of weakly absorbing thin films. The measurement is based on an accurate determination of the reflectance and transmittance of a specimen illuminated by a laser beam. The laser beam is incident on a transparent substrate coated with the film to be evaluated, with an angle of incidence equal to the Brewster angle for the substrate, and its polarization can be switched between the p and s states. If the thickness is known to be within a presumptive range, measurements of the p and s reflectance and transmittance allow a calculation of the optical constants n, k and the thickness of…
Mapping Carbon Stocks In Central And South America With Smap Vegetation Optical Depth
2019
Mapping carbon stocks in the tropics is essential for climate change mitigation. Passive microwave remote sensing allows estimating carbon from deep canopy layers through the Vegetation Optical Depth (VOD) parameter. Although their spatial resolution is coarser than that of optical vegetation indices or airborne Lidar data, microwaves present a higher penetration capacity at low frequencies (L-band) and avoid cloud masking. This work compares the relationships of airborne carbon maps in Central and South America with both (i) SMAP L-band VOD at 9 km gridding and (ii) MODIS Enhanced Vegetation Index (EVI). Models to estimate carbon stocks are built from these two satellite-derived variables.…
Demonstration of an efficient pumping scheme for a 7.36-nm Ni-like samarium soft x-ray laser
2010
The demonstration of a 7.36 nm Ni-like Sm soft x-ray laser pumped by 36 J of a Nd:glass chirped pulse amplification laser is presented. Double-pulse single-beam non-normal incidence pumping was applied for the efficient soft x-ray laser generation. Here the applied technique included a new single optic focusing geometry for large beam diameters, a single-pass grating compressor traveling-wave tuning capability and an optimized high energy laser double-pulse. This scheme has the potential for even shorter wavelength soft x-ray laser pumping.
Ytterbium-doped fibers for high-power fiber lasers
2021
Ytterbium (Yb) doped optical fibers are widely used in high-power applications and ultrafast lasing since they show adequate power-handling capability and provide desirable beam quality. Yb-doped fibers with large core area can support high power but often act as a multimode fiber and compromise the output beam quality. Hence, it is important to attain a proper balance between the power-handling capability and the beam quality. Yb-doped fibers as a gain medium in pulsed fiber laser systems are prone to nonlinear optical effects due to the presence of high peak power in the ultrashort pulses. Nonlinearity such as self phase modulation (SPM) affects the width and the shape of the pulse, both …
MoSi2 laser cladding—elaboration, characterisation and addition of non-stabilized ZrO2 powder particles
2003
International audience; The cladding process using laser beam radiation comprises different operational regimes, depending on the involved lasers (usually CO2 or Nd:YAG) and materials. A series of experiments has been carried out to investigate Nd:YAG laser cladding using MoSi2 powder. Procedures and operating parameters for producing clad layers has been developed and their properties evaluated. The feasibility of the laser cladding technique, using a high power Nd:YAG laser, by projecting MoSi2 powder on steel substrate was demonstrated. The results indicate a low density of cracks, elevated powder catchment efficiency (between 65 and 90%) and hardness values around 1200–1300 HV. Our goal…
Magnesium alloys (WE43 and ZE41) characterisation for laser applications
2004
International audience; One of the most important parameters in laser treatment is the quantity of beam energy absorbed by the substrate. Despite its important role played in laser processes, this factor is rarely available for the laser sources wavelengths and at high temperatures reached during such treatments. A series of experiments were carried out in order to characterise, from this point of view, two types of magnesium alloys, WE43 and ZE41, often used in laser applications (cladding, alloying, welding, etc.). The results represent an important step in order to understand Mg-alloys behaviour under laser beam action.
MoSi2 laser cladding—A new experimental procedure: double-sided injection of MoSi2 and ZrO2
2003
International audience; In the last decade, development of low density advanced material systems for service at temperatures up to 1300 °C was one of the goals of many researches. This kind of material should mainly have moderate fracture toughness and should exhibit oxidation resistant behaviour at low and intermediate temperature. One of the most studied materials continues to be the intermetallic compound MoSi2. The molybdenum disilicide has been considered as an attractive candidate due to its melting point (2030 °C) and excellent oxidation resistance at high temperatures. The main problem associated with the MoSi2 layer synthesized using laser beam is the layer fragility. To avoid this…
Light scattering - diagnostic methods for colloidal dispersions
1993
Abstract The increasing demand from the colloid research community for quick and noninvasive experimental techniques as well as the rapid progress of modern optics and electronics have led to a considerable expansion in the field of light scattering. This review introduces the basic concepts with some emphasis on novel approaches like the study of interacting particle systems, multiple scattering techniques, and non ergodic samples. Particular attention is then devoted to recent experimental progress towards more compact and rugged instruments.