Search results for "laser"
showing 10 items of 3161 documents
A new control parameter to predict micro-warping-induced job failure in LPBF of TI6AL4V titanium alloy
2023
Abstract Laser powder bed fusion (LPBF) includes a few printing techniques widely used, in recent years, concerning the additive manufacturing of Ti6Al4V alloys. These produced parts, typically utilized in sectors such as aerospace and biomedical, are characterized by very high added value. It is therefore fundamental to identify the influence of process parameters typical of LPBF technology on the occurrence of warping leading to process failure. This study deals with the characterization of single-track and “micro-scale” level warping phenomena which may lead to protrusion of material over the powder bed and process failure before normal termination. This phenomenon was investigated as a …
Environment assisted photoconversion of luminescent surface defects in SiO 2 nanoparticles
2017
Abstract Time-resolved photoluminescence investigation on SiO 2 nanoparticles was carried out in controlled atmosphere, with the aim to discern the effects induced on the typical blue luminescence band by high power UV Nd:YAG laser photons (4.66 eV) and by some selected molecular species of the air (O 2 , N 2 , CO 2 , H 2 O). These factors ultimately determine both the brightness and photostability of the emitting defect, so as to limit the unique and attracting potentialities offered by this system in many applicative fields. Here it is highlighted that the effects due to photons and molecules, singularly considered, are not additive, the radiation being more dramatic in reducing the emiss…
Numerical and Experimental Analysis of Convection Transfer During Melting by a Mono-Pulsed Laser
2010
This paper presents a comparison between simulation and experimental results of the melting process of metallic material by a pulsed laser source Nd-YAG. Variations of the thermophysical properties were considered. Furthermore, the model included the effects of the surface-tension gradient on the fluid surface and the buoyancy force. The keyhole effect induced strong surface deformations and often formed cavities, which arre undesirable in the surface treatment process. An experimental study of the surface profile of the melted zones was also conducted to seek a relationship between the so-called keyhole effect and the laser triangulation measurements. The predicted Laser Melted Zone (LMZ) …
Trace detection of plutonium by three-step photoionization with a laser system pumped by a copper vapor laser
1985
Laser photoionization has been used to detect trace amounts of plutonium. A high sensitivity and selectivity has been achieved by applying three-step excitation and ionization of the plutonium atoms with high pulse-repetition rates and additional mass determination by time-of-flight measurements. A laser system was developed which consists of a copper vapor laser pumping three dye lasers simultaneously. Samples containing between 1010 and 1012 atoms of239Pu on Re filaments were measured yielding strong resonance signals with maximum ion count rates of several kHz at a vanishingly low background. A detection efficiency of 10−7 was determined allowing the detection of about 108 plutonium atom…
Accurate tuning of mismatched twin-core fiber filters
1998
We have demonstrated a reproducible and accurate way of tuning the coupling wavelength of a mismatched twin-core filter. This method allows high quality all-fiber filters to be implemented with low loss at any desired wavelength over a range of few hundred nanometers from the same fiber. An ~500-nm tuning range is demonstrated, limited only by the measurement setup and not by the technique itself. Highly accurate control of the filtering wavelength in combination with control of filtering strength by adjustment of the length of the twin-core fibers allows complex filter profiles to be implemented by cascading of several different filters. These filters are also very stable to a change in te…
Contribution to the study of physico-chemical properties of surfaces modified by last treatment : application to the enhancement of localized corrosi…
2011
Metallic materials are more and more used in severe conditions with particularly strong request for improving their behavior in aggressive environment and especially over long periods. The objective of this PhD work is to estimate the potentiality of a laser surface melting treatment on the improvement of the stainless steel 304L corrosion resistance, surface treatments by laser can be revisited on the basis of a recent change in the laser technology. In the frame of this work, a nano-pulsed laser fiber was chosen : it allows the treated surface to be melted for few microns in depth, followed by an ultra-fast solidification occuring with cooling rates up to 1011 K/s. The combination of thes…
Interference-assisted detection of dark photon using atomic transitions
2019
Dark photon is a massive vector particle which couples to the physical photon through the kinetic mixing term. Such particles, if exist, are produced in photon beams and, in particular, in laser radiation. Due to the oscillations between the physical photon and the dark photon, the latter may be, in principle, detected in the light-shining-through-a-wall experiment. We propose a variant of this experiment where the detection of dark photons is based on the atomic transitions. The key feature of this scheme is that the detection probability is first order in the coupling constant due to the interference term in the photon and dark photon absorption amplitudes. We expect that such experiment …
Reconfigurable waveguides defined by selective fluid filling in two-dimensional phononic metaplates
2022
Abstract We investigate two-dimensional phononic metaplates consisting of a periodic array of cups on a thin epoxy plate that is perforated with periodic cross holes. The cups are individually filled with water or remain empty, in view of creating reconfigurable phononic waveguides. Phononic band gaps exist for empty or filled epoxy cups, leading to waveguides defined with either positive or negative contrast. Straight and 90° bent waveguides are considered experimentally. Lamb waves are excited by a piezoelectric patch glued onto the metaplate and are imaged using a scanning laser vibrometer. Experimental results are compared to a three-dimensional finite element model of fluid–structure i…
Spin-orbit, radial, and angular coupling effects in the NaRb excited states
2009
Spin-orbit, radial, and angular nonadiabatic matrix elements between the lowest excited states of NaRb are evaluated by quasi-relativistic ab initio methods, and the results accompanied by potential curves, permanent and transition moments are compared with experimental data and preceding calculations.
Beam matching with space charge in energy recovery linacs
2019
Abstract Matching with space charge of an Energy-Recovery Linac (ERL) arc into the subsequent RF structure is essential to preserve beam quality. We show how to match beam envelopes and dispersion along the bends and recirculation arcs of an ERL, including space charge forces, in order to adjust the beam to the parameters of the subsequent RF structure. For a qualitative analysis, we show that one can use a beam matrix approach together with the smooth focusing approximation but with longitudinal–transverse coupling. It is also shown that the space-charge-modified dispersion plays a key role for the adjustment of the momentum compaction R 56 required for both the isochronous and the non-iso…