Search results for "laser beam"
showing 10 items of 141 documents
Numerical support for laser welding of zinc-coated sheets process development
2002
Abstract A lap welding process for zinc-coated sheets has been developed with the help of numerical simulations. This process has been improved and is now compatible with industrial requirements. The zinc boiling point (1180 K) is lower than the steel melting point (1800 K). Consequently, a violent boiling of zinc in melted steel produces serious defects in the seam. To get round this difficulty, we choose to consider a two-spots process: the first spot vaporizes the zinc coating at the interface; the second one welds the sheets. Previously, we develop a numerical model that permits a process parameters choice and limits the plan of experimentations. The zinc ablation spotlight shape is cho…
Laser beam scattering effects in non-absorbent inhomogenous polymers
2007
Ilie, Mariana Kneip, Jean-Christophe Mattei, Simone Nichici, Alexandru Roze, Claude Girasole, Thierry; In this paper a numerical model for laser beam scattering in the semi-transparent polymers is presented, using a Monte Carlo algorithm and the Mie theory. The algorithm correctly accounts for the independent multiply-scattered light. We describe the algorithm, present a number of important parameters that account in the welding process, and explicitly show how the algorithm can be used to estimate the laser beam intensity both inside the semi-transparent component and at the welding interface and the beam widening. For the model validation an experimental bench test has been realized and s…
Use of pure vanadium and niobium/copper inserts for laser welding of titanium to stainless steel
2020
Abstract Niobium and vanadium have high metallurgical compatibility with titanium and therefore can be used as inserts to avoid the accumulation of brittle intermetallic phases such as Fe2Ti during the fusion welding of titanium alloys with steels. In the present study, the continuous double pass welding of 1 mm thick Ti-6Al-4V alloy and 316 L stainless steel plates through several mm wide pure vanadium or niobium insert was studied. In case of a vanadium insert, a beam offset on the vanadium was found to produce cold crack formation in vanadium/316 L melted zones containing more than 40 wt.% V despite the absence of σ phase. Whereas a centered beam position and offset on the steel side pro…
Numerical investigation of laser beam shaping for heat transfer control in laser processing
2002
This article presents a thermal finite volume model adapted to investigate laser processes. It is specially developed to treat moving heat sources with phase changes, melting and vapourisation. Heat transfer control in laser processing is particularly useful when processes must respect prescribed temperatures, or more generally, prescribed constraints. These processes involve generally several laser sources, or non-conventional power distribution. Hence, they have numerous parameters to set. Experimental optimisation is difficult and may be expansive. The numerical model is a useful and cheaper tool for development of those complex processes. For example in this article, two special laser p…
Continuously tunable diamond Raman laser for resonance laser ionization.
2019
We demonstrate a highly efficient, tunable, ∼5 GHz line- width diamond Raman laser operating at 479 nm. The diamond laser was pumped by a wavelength-tunable intra- cavity frequency-doubled titanium sapphire (Ti:Sapphire) laser operating at around 450 nm, at a repetition rate of 10 kHz with a pulse duration of 50 ns. The Raman reso- nator produced a continuously tunable output with high stability, high conversion efficiency (28%), and beam quality (M$^{2}$ <1.2). We also demonstrate that the linewidth and tunability of the pump laser is directly transferred to the Stokes output. Our results show that diamond Raman lasers offer great potential for spectroscopic applications, such as resonance…
A review of the development of portable laser induced breakdown spectroscopy and its applications
2014
Abstract In this review, we present person-transportable laser induced breakdown spectroscopy (LIBS) devices that have previously been developed and reported in the literature as well as their applications. They are compared with X-ray fluorescent (XRF) devices, which represent their strongest competition. Although LIBS devices have advantages over XRF devices, such as sensitivity to the light elements, high spatial resolution and the possibility to distinguish between different layers of the sample, there are also disadvantages and both are discussed here. Furthermore, the essential portable LIBS instrumentation (laser, spectrograph and detector) is presented, and published results related…
Continuous-wave, double-pass second-harmonic generation with 60% efficiency in a single MgO:PPSLT crystal
2014
We present a double-pass scheme for high-efficiency, high-power, second-harmonic generation (SHG) in a single MgO-doped periodically poled stoichiometric lithium tantalate (MgO:PPSLT) crystal. The device is pumped by a single-frequency, continuous-wave fiber amplifier laser system at a wavelength of 1091 nm. For the double-pass scheme, a conversion efficiency of 60% and a harmonic power of 12.8 W at a wavelength of 545.5 nm with a high beam quality of (M2<1.2) is achieved. Compared to single-pass SHG, a double-pass enhancement factor of more than two is observed at the highest fundamental pump power.
Influence of laser beam profile on the generation of ultrasonic waves
2011
The different ultrasonic fields generated in metallic materials by a laser beam with flat and Gaussian profile are investigated experimentally and using the finite element method (FEM). A high power laser beam irradiating a solid surface produces elastic waves with a mechanics that depends on many parameters, including the profile of the laser beam. The influence of the beam profile is investigated with the FEM analysis, considering the temperature dependence of material properties.
Characterisation of cw Nd : YAG laser keyhole dynamics
2001
Abstract The paper concerns laser–matter interaction characterisation. In this work, we use a rapid CCD camera located coaxially to the laser beam and we compare recorded images with those obtained by numerical modelling. Because images are difficult to understand, we compute thermal radiation emitted by a keyhole of fixed geometry and we adjust it trying to approach the camera record. The modelling treats radiative heat transfer within the keyhole and determines the sensor illumination map. By adjusting the geometrical characteristics of the hole, we seek to obtain the image that corresponds as well as possible to the realised experiment. Results are compared with other experimental method…
Improved noncontact optical sensor for detection of glucose concentration and indication of dehydration level.
2014
The ability to extract different bio-medical parameters from one single wristwatch device can be very applicable. The wearable device that is presented in this paper is based on two optical approaches. The first is the extraction and separation of remote vibration sources and the second is the rotation of linearly polarized light by certain materials exposed to magnetic fields. The technique is based on tracking of temporal changes of reflected secondary speckles produced in the wrist when being illuminated by a laser beam. Change in skin’s temporal vibration profile together with change in the magnetic medium that is generated by time varied glucose concentration caused these temporal chan…