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A theoretical estimation of local heating of a material during single and multiple filamentation of series of femtosecond laser pulses in a LiF crystal is obtained. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is a powerful method that furnishes detailed information on various carbon allotropic forms, via a set of vibrational lines, the so-called Raman “fingerprints”. Depending on the rolling up of a graphene (2D carbon network system), it obtains a single-walled carbon nanotube (SWCNT, 1D network system) or a C60 (0D) fullerene molecule, whose Raman spectra vary noticeably, enabling one to differentiate between these types of carbon materials. SWCNTs can be filled with fullerene molecules, forming the so-called peapods, whose properties are attractive in terms of a possible superconductivity by alkaline metal doping. In this case, the Raman spectra contain the “signatures” of both SWCNTs and fullerenes, ensuring information on the type of encapsulating fullerene molecules, as well as on the diameter distribution of SWCNTs, receiving fullerenes. In this respect, the present work aims the Raman spectroscopy characterization of a sample of C60@SWCNTs peapods, prepared via a multistep method, in order to confirm the presence of fullerene molecules (C60) inside the tubes, as well as to show the convenience of Raman spectroscopy for the non-destructive and rapid analysis of such combined-dimensionality systems. The Raman responses of SWCNTs were distinguished from those of fullerene molecules. Furthermore, the Raman spectra of peapods, excited by a 325-nm laser beam, reveal the formation of bonds between the fullerene molecules in the nanotubes, presumably due to the laser heating (photopolymerization processes). [ABSTRACT FROM AUTHOR]

The performance properties of machine parts can be significantly improved by laser processing of their surfaces using modifying the melt with nanoscale particles of refractory compounds (carbides, nitrides, carbonitrides, etc.). Nano-sized particles increase the number of crystallization centers and, thus, refine the macrostructures of the solidified metal, improve quality, and harden the surfaces being processed. Thermophysical processes in a moving metal substrate under the action of laser radiation on its surface are investigated by numerical simulation methods. A mathematical model describing the steady-state thermophysical processes in the surface layer of a metal, in particular, the influence of nanoscale powder on the nucleation and growth of the solid phase, is considered. According to the results of numerical experiments, the distribution of the temperature field, the size of the crystallization zone, the area of the treated surface of the substrate, depending on the speed of its movement and the power of the laser radiation, are estimated. [ABSTRACT FROM AUTHOR]

The AFP process, is a promising automated deposition technique for carbon fibers pre-impregnated polymer composites. It is nowadays more and more popular for the development of complex shapes in the aerospace industry. The improvement of high performances thermoplastic polymers (PAEK family) offers the possibility of enhanced and faster processes. This process has become really popular also in the scientific community, where a lot of attention was paid to different aspects: (i) efficient numerical modeling, (ii) complex laser-composite interaction, (iii) effect of the processing parameters. Surprisingly, very little question arose about the thermal behavior under the extreme conditions imposed by the laser heating. Heat transfers occurring during the heating step still require a reliable measurement, partly because the measurement of temperature directly on the process is uneasy. This study offers to step aside from such difficulties by developing a specific static instrumented bench aiming at determining what do the prepreg tape and substrate undergo during deposition in terms of temperatures and heat flux fields. The whole device enables to reach easily the melting temperature of the PEEK (~350°C) in the range of 25ms, which is aimed at being representative of a fast industrial deposition. Results show several important results: (i) comparing two materials with different microstructures and identical fiber fractions, results highlight the huge importance of the fiber distribution on the thermal behavior ; (ii) a surfacic heat source model is not sufficient to predict the temperature elevation so that the laser/composite interaction has to be accounted for by a volumic heat source ; (iii) the thermal contact resistance (TCR) with the metallic substrate is huge, and in the very short time range of the process, cannot be modeled by a usual TCR model, capacitive effects have to be taken into account. [ABSTRACT FROM AUTHOR]

Carbon dioxide laser was irradiated on the graphite particles adhered on a copper plate through waterglass in order to prepare graphite-dispersed copper composite on a surface of a copper plate. The particles which were not removed with ultrasonic cleaning were judged to be adhered on the copper. The graphite particles at the laser spot were heated with the laser ablation, and these particles adhered on the copper plate. This originates in that wettability between graphite and molten copper was improved at a higher temperature by the laser heating. The carbon content at the laser spot decreased with the increase in the laser irradiation time, because the graphite particles at the laser spot were removed by the laser trapping. The electric resistance reduced to around 1 Ω. The graphite particles at the outside of the laser spot adhered on the copper plate through the waterglass by conduction heat from the laser spot. The particles were eliminated by the ultrasonic cleaning during insufficient heat hardening of waterglass. Therefore, carbon content increased with the increased in the laser-irradiation time. The electric resistance at the outside of the laser spot increased to around 17 Ω. [ABSTRACT FROM AUTHOR]

An overview of the containerless, ultra-high temperature instrumentation on the high energy x-ray beamlines at the Advanced Photon Source is described. It has been implemented for the specific goal of studying crystalline transitions in radioactive materials. The experiments employ laser heating combined with aerodynamic levitation and are designed to recreate severe accident scenarios in the laboratory to benchmark atomic interactions under meltdown and post-meltdown conditions. A hermetically sealed chamber enables control of the atmosphere chemistry surrounding a floating pellet of nuclear material, 2-3 mm in diameter. Optical pyrometery enables instantaneous feedback of the sample surface temperature, and a focused 400 W CO2 laser beam incident on a sample can typically achieve temperatures up to 3500 K. The penetration associated with high energy x-rays (cf. 100 keV) is required to enable transmission diffraction measurements in sealed complex environments. Rapid, high flux x-ray experiments on nuclear materials provides the ability to probe phase transitions and determine reaction pathways upon cooling. Phase identification and the calculation of phase diagrams from different compositions of the model corium system UO2:ZrO2 show the single phase tetragonal structure exists at lower temperatures than previously reported. [ABSTRACT FROM AUTHOR]

The co-axial Laser Cladding (LC) is one of the most advanced surface treatment processes where generally a superior powder or wire material is deposited on the substrate to improve surface properties by using laser heat source. In this work, a physical model of the clad and the substrate has been presented. An attempt has been made to describe the simplified relation of temperature, stress and strain with time by using the established theoretical knowledge of generation of stress and strain after thermal treatment. The simplified relation of temperature, stress and strain with time has been explained with the help of schematic diagrams. The finding of this study will help to understand the temperature, stress and strain behaviour with time in the Laser Cladding process. [ABSTRACT FROM AUTHOR]

It has been experimentally proved that it is possible to produce a metal capillary structure with significant capillary action and free shape configuration using selective laser melting. Capillaries are created by dividing the solid detail volume into micro-sized parallel walls with roughness as a result of SLM 3D printing. Experiments are conducted on aluminum powder with particle size in the range of 10-40 μm (,) and distances in 3D model between surfaces incapillary generation zone in the range of 50-200 μm. It is showed that products produced from model with 100 μm gaps have the greatest efficiency of fluid lifting as a result of obtaining stable arrays of capillaries of 20-40 μm in size. Change in the direction of (growing) printingthe product doesn't significantly influence on capillary geometry, but it affects on safety of the structure. [ABSTRACT FROM AUTHOR]

Understanding the physics of laser-matter interactions in ultrashort pulses is important for many well-acknowledged applications from material modifications to biology. We numerically and experimentally consider the effect of sub-picosecond Ti:sapp laser actions on 60-100 nm gold films mounted onto a fused silica substrate. The pulse energy is sufficient to ablate the films. For the first time, we show that there are different regimes of ablation, and the formation of the 3D structures depends on the value of the absorbed fluence Fabs and the adhesion strength padh between the film and the substrate. Namely, a delamination threshold Fdelam and an ablation threshold Fabl (Fdelam < Fabl) exist if adhesion is weak. Above the lower threshold Fdelam, the whole film delaminates from the substrate. Above the higher threshold Fabl, the thin film ruptures near its middle plane. The external half of the film flies away, while the internal half remains on the glass substrate. There are two thresholds Fdelam and Fabl for the Au/glass and Ag/glass targets, because pure gold and silver are weakly coupled to the glass. The lower threshold Fdelam disappears in the case of a strong adhesion stress padh. Consequently, delamination as a whole becomes impossible. Although the rupture of a film remains because the ablation threshold Fabl is independent of on adhesion. Adhesion is high when an intermediate thin layer of chromium is placed between the gold and the glass. The film velocity after it separates from the substrate is low for the range of fluences Fdelam < F < Fabl because the acoustic impedance Zglass of glass is small relative to the impedance Zfilm of a gold film. Therefore, during an evolution, the absolute values (positive or negative) of the contact pressures are few times smaller than the absolute pressures in a gold film. However, above the ablation threshold Fabl < F, the velocity of the external part of a film becomes few times larger because the velocity is independent of the acoustic impedance of a substrate. These circumstances explain why 3D structures such as nanojet above the microbump appears in the case of a weak adhesion. The velocity should be not too large to allow to the surface tension and crystallization to stop an inflation and breakaway of a microbump. [ABSTRACT FROM AUTHOR]

We have developed thermal impulse sensors to measure and record temperature and heating duration in explosive fireballs. The functionality of these sensors is similar to that of our temperature-only sensors - rare-earth ions are used to monitor temperature-induced phase changes. However, in this case two sensor materials, p-Dy:Y2O3 and p-Eu:ZrO2, with different phase change kinetics are mixed. In addition, a fluorescence standard, Ho:ZrO2, is included. Also, using laser heating, we have now reduced the shortest heating duration for our calibration measurements from the previously reported 2 s to 100 ms, and we have evaluated these sensors for temperatures between 400 °C and 900 °C, and heating times between 100 ms and 1000 ms. Using spectral matching, we determine the temperature and heating duration. [ABSTRACT FROM AUTHOR]

In the context of processing long-fiber reinforced thermoplastic composites with laser-heating, the spatial distribution of the heat flux is one of the main parameters which controls the induced processing temperature. Unfortunately, the illuminated geometry might be not trivial, and the optical properties related to absorption and scattering phenomena of such a material are not well-established. In order to study and characterize the laser/composite interaction at the scale of the micro-structure, a model based on multiple cylinders is envisaged. The method consists in the calculation of a semi-analytical solution for the electromagnetic scattering from an array of circular cylinders due to an obliquely incident plane wave. [ABSTRACT FROM AUTHOR]

When the common deformation processes are scaled down to micro/meso dimensions, size effect is the particular phenomena in microforming, which is related to the dominant influence of single grains inside the micropart. The conventional cross wedge rolling (CWR) is introduced into the micro scale in order to take the advantages of CWR. The micro cross wedge rolling (MCWR) has to confront with the phenomena of size effect that occurs in the common microforming processes inevitably. One of the approaches to compensate size effect is to increase the deforming temperature. An increased formability is achieved because more slip systems of polycrystal metal are activated at the elevated temperature. This reduces the anisotropic material behavior resulting in a more homogeneous forming with improved reproducibility. In this study, a YAG laser beam is applied to heat the workpiece. Finite element model (FEM) associated with a material constitutive formulation considering dislocation mechanics is set up to simulate the MCWR of pure copper utilizing the laser heating. The surface asperity as an indication of material heterogeneity in micro scale is quantitatively analysed. The simulation results show a good agreement with experimental results in terms of the surface asperity. [ABSTRACT FROM AUTHOR]

We will discuss results of combined experimental and theoretical investigations of ablation and laser-driven shock-wave phenomena in metal films irradiated by femtosecond laser pulses. The femtosecond interferometric microscopy technique was used to make time-resolved measurements of optical properties as well as record the deformation dynamics at both the rear and frontal surfaces during initial two-temperature electron-ion relaxation and subsequent hydrodynamic expansion. In conjunction with experiment, the formation and propagation of strong tensile and compression waves were investigated by a combination of two-temperature hydrodynamic modeling and molecular dynamics simulations. The experimental tensile strengths of aluminum and nickel in solid and liquid states at extremely high strain rates in range 108÷109s-1 were obtained from the time evolution of rear and frontal surface velocities. Theoretical tensile strengths calculated by atomistic simulations of ablation and spallation using micron-sized films agree well with experiment. Elastic-plastic response of metallic films to shock compression investigated by both experiment and theory/modeling will also be discussed. [ABSTRACT FROM AUTHOR]

A new scanning laser hear has been designed for measuring up to 6 degrees of freedom at a point. The scanning head is supported by a rotating hallowed shaft, which allows the laser beam to travel up to the scanning head. A set of two mirrors deflects the laser beam with an angle and the rotation of the scanning head produces a conical scan. This work shows that this device can perform a conical scan whose the very small circle scan, before and after the focus point, can measure up to 6 degrees of freedom; the paper focuses on the in-plane rotation. A validation of the novel scanning head is performed. This paper concludes with the presentation of a more compact design for the 6DOF scanning head, which is aimed for complex engineering applications. [ABSTRACT FROM AUTHOR]

Exploration of behavior of hydrogen at extremely high pressures and temperatures in diamond anvil cells has been challenging on account of its high reactivity and diffusivity. Recently, we have developed novel methods to confine hydrogen under extreme conditions and perform spectroscopic studies from a highly localized hot sample region in a laser heated diamond anvil cell. Further, a virtual experiment control and data acquisition system has been developed to perform fully automated Raman spectroscopy measurements while samples are laser heated from both sides. The consequent large reduction in the effective measurement time in combination with good local confinement of the sample has enabled tracking the vibron behavior up to ∼140 GPa and >1500 K. [ABSTRACT FROM AUTHOR]

We report setting up of an Nd-YAG laser (1.06 μm) based Laser Heated Diamond Anvil Cell (LHDAC) facility to carryout High Pressure High Temperature (HPHT) experiments. Pressure is generated by squeezing sample between diamond anvils using Mao-bell type DAC and high temperature is realized by focusing an Nd-YAG laser onto the pressurized sample inside the DAC. HPHT synthesis of WGe2 has been carried out using Nd-YAG LHDAC facility. [ABSTRACT FROM AUTHOR]

We report setting up of an Nd-YAG laser (1.06 μm) based Laser Heated Diamond Anvil Cell (LHDAC) facility to carryout High Pressure High Temperature (HPHT) experiments. Pressure is generated by squeezing sample between diamond anvils using Mao-bell type DAC and high temperature is realized by focusing an Nd-YAG laser onto the pressurized sample inside the DAC. HPHT synthesis of WGe2 has been carried out using Nd-YAG LHDAC facility. [ABSTRACT FROM AUTHOR]

GexC1-x is expected to be a wide band gap semi conductor. But the synthesis of this material in bulk by conventional equilibrium methods at atmospheric pressure is not possible as it is not energetically favorable. In this paper we report evidence for formation of Ge-C bonds using Laser Heated Diamond Anvil Cell (LHDAC) technique at P ∼9.3 GPa and ∼2000 K after prolonged heating for ∼30 minutes. The temperature quenched sample was characterized by in-situ Raman spectroscopy at 300 K. The Raman spectra at various regions of the laser heated sample at 9.3 GPa and at 300 K shows in addition to the characteristic Ge TO(&Gamma) and C phonon mode, both of which are considerably softened, a new mode appearing at 203.3 cm-1. We ascribe these to Ge-C bond formation. [ABSTRACT FROM AUTHOR]

GexSn1-x has been predicted to be a direct band-gap semiconductor, but attempts to synthesize this in bulk form by conventional synthesis methods have not been successful on account of the poor solubility of Sn in Ge. In this work, laser heated diamond anvil cell (LHDAC) technique has been employed to explore formation of bulk GexSn1-x (x = 0.7) at varying pressures and temperatures. At ∼8 GPa, in situ micro-Raman spectroscopy done on several regions of temperature quenched samples laser heated up to ∼2000 K reveals vanishing of the intense Ge TO(Γ) phonon at ∼326 cm-1 and appearance of a softer mode, concurrent with appearance of a new high intensity Raman mode at ∼660 cm-1. These indicate dilation of the Ge-Ge bond by virtue of significant miscibility of βSn at these high P-T conditions and hints at formation of new stiff Ge-Sn bonds. [ABSTRACT FROM AUTHOR]

High pressure synthesis of BSb has been attempted using Laser Heated Diamond Anvil Cell facility with a CO2 laser. B:Sb in 3:1 atom ratio was laser heated at ∼7 GPa , 10 GPa and 30 GPa. In-situ characterization of the pressurized sample was done by micro-Raman technique. The micro-Raman results before and after laser heating at different pressures did not indicate compound formation. Also, Sb, which shows a series of structural transitions under pressure up to 30 GPa did not show any metastable phase in the P and T regime studied. [ABSTRACT FROM AUTHOR]