Laser Heating Conditions Research Articles

Absence of superconductivity in I4/mmm-FeH5: experimental evidence.

The experimentally discovered FeH5 exhibits a structure built of atomic hydrogen that only has bonding between hydrogen and iron atoms [C. M. Pepin, G. Geneste, A. Dewaele, M. Mezouar and P. Loubeyre, Science, 2017, 357, 382]. However, its superconductivity has remained unsolved since its discovery. In this work, we have synthesized I4/mmm-FeH5 at 139 GPa combined with laser-heating conditions. The electrical resistance measurements at ultrahigh pressures indicate that no evidence of superconducting transition of FeH5 is observed in the temperature range of 1.5 K to 270 K. These results indicate that I4/mmm-FeH5 does not exhibit superconductivity within the experimental temperature range, and the introduction of iron atoms is not beneficial to the formation of the superconducting phase.

Thermographic Inspection Simulation of One Kind of Rail Defects

Rail is an important foundation of rail transit, and defects on the rail may pose a serious threat to rail transit. As a new non-destructive testing method, thermographic detection shows an excellent application prospect. In order to verify whether thermographic detection technology can be used to detect the defects on the rail, especially the defects at the bottom of the rail. The ANSYS software is used to model the rails under different conditions, and the heat flow simulation experiment is carried out to obtain the temperature change results when the heat flow passes through the defects and when it does not. The existence and location of defects can be determined by observing how the heat flow changes due to the existence of defects.Although the results show that surface fracture defects and defects towards the bottom edge of the rail can be clearly detected by thermal modeling under laser heating conditions, for transverse cracks that exist near the center of the rail bottom, the simulation experiments still cannot distinguish the temperature differences at the same observation location under current parameters. So it may be necessary to further optimize the experimental process, or increase the experimental parameters, so that the thermal modeling method can be better applied for non-destructive testing of rail defects.

Multi-extreme conditions at the Second Target Station.

Three concepts for the application of multi-extreme conditions under in situ neutron scattering are described here. The first concept is a neutron diamond anvil cell made from a non-magnetic alloy. It is shrunk in size to fit existing magnets and future magnet designs and is designed for best pressure stability upon cooling. This will allow for maximum pressures above 10GPa to be applied simultaneously with (steady-state) high magnetic field and (ultra-)low temperature. Additionally, an implementation of miniature coils for neutron diamond cells is presented for pulsed-field applications. The second concept presents a set-up for laser-heating a neutron diamond cell using a defocused CO2 laser. Cell, anvil, and gasket stability will be achieved through stroboscopic measurements and maximum temperatures of 1500K are anticipated at pressures to the megabar. The third concept presents a hybrid levitator to enable measurements of solids and liquids at temperatures in excess of 4000K. This will be accomplished by a combination of bulk induction and surface laser heating and hyperbaric conditions to reduce evaporation rates. The potential for deployment of these multi-extreme environments within this first instrument suite of the Second Target Station is described with a special focus on VERDI, PIONEER, CENTAUR, and CHESS. Furthermore, considerations for deployment on future instruments, such as the one proposed as TITAN, are discussed. Overall, the development of these multi-extremes at the Second Target Station, but also beyond, will be highly advantageous for future experimentation and will give access to parameter space previously not possible for neutron scattering.

Laser heating conditions for copper sphere implantation into borosilicate glass

Implanting metals in glass can serve many different purposes, ranging from enhancing the electro-optical properties to modifying the mechanical properties of the substrate. One approach involves the use of continuous laser illumination to implant metal spheres by transferring particles from a metal foil in direct contact with one side of the glass substrate. The process, which occurs in a very short period time (in tens of milliseconds), is unidentified: due to the bright thermal emissions, it cannot be directly observed. In this study, the continuous laser heating conditions required for implanting copper spheres in borosilicate glass were investigated via spectroscopy and numerical calculations to estimate the temperature of the copper foil. Emission spectroscopy revealed that the temperature during implantation reached 5100 K, which largely exceeded the temperature threshold for laser absorption (∼2000 K). Under such conditions, the plasma forms and enables the migration of copper particles into the glass host. The plasma propagation speed increased with increasing laser power density. The copper sphere was implanted when the plasma propagation speed was 20–50 mm/s. The copper sphere could not be implanted, and fiber fuse occurred when the plasma propagation speed was higher than 50 mm/s.

Non-scanning wide range multi-wavelength imaging temperature measurement technology

Multi-wavelength temperature measurement technology is an advanced radiation temperature measurement technology, which assumes a functional relationship between emissivity and spectrum. The measured multi-wavelength radiation signals and the function relationship between emissivity and spectral is used to obtain the true temperature and emissivity of the target. Multi-wavelength imaging temperature measurement technology detects the multi-wavelength radiation image information of the target and inversely calculates the temperature field distribution of the target. Aiming at the inadequacy of color CCD-based multi-wavelength imaging temperature measurement, such as adaptability of the nonlinear spectral emissivity model, and the narrow dynamic range of temperature measurement, and so on, a four-wavelength non-scanning imaging temperature measurement method based on non-equal ratio filter color splitting at the diaphragm was proposed. This method could effectively compress the band imaging bandwidth to form four narrow band imaging detections, and was suitable for wide dynamic range temperature field measurement of nonlinear spectral emissivity model targets. A four-wavelength imaging thermometer was developed according to the proposed temperature measurement method. The thermometer was mainly composed of a window, a neutral optical attenuator, a four-color filter, an optical objective lens, a visible/near infrared integrated sensor, a measurement control unit, and software. The real temperature distribution of the target was obtained according to the multi-wavelength warming algorithm by the thermometer software. The target high-temperature field (800-2500 ℃) was tested under laser heating conditions. The comparison between the measurement result and the thermocouple data shows that the error is less than 1%, and the method has higher accuracy and better dynamic range adaptability.

Temporal and spatial temperature modelling for understanding pulsed laser induced solution based nanomanufacturing

Recently, pulsed lasers have demonstrated great potential in targeted synthesis in solution based nanomanufacturing, realizing high precision and accuracy in space, time and energy input. The unique temperature history induced by pulsed lasers is indispensable to understand the related fundamentals and to realize the precision control of deposition. In this study a heat transfer model was developed and applied to predict the temporal evolution and the spatial distribution of pulsed laser induced temperature change across the reaction sites. Chemically deposited ZnO crystals were studied as an example, showing the relationships among laser parameters and heating conditions, and deposited crystal characteristics. Peak temperature and heat accumulation induced by pulsed laser were found to affect deposited crystal number density and size. The nucleation number density distribution was found to be correlated with the spatial temperature distribution and inversely proportional to the crystal size. The presented heat transfer model is a crucial tool to understand crystallization fundamentals and it is essential for facilitating pulsed laser as a new tool for research, design, manufacturing and control.

Study of Optical Properties of Surface Layers Produced by Laser Surface Melting and Laser Surface Nitriding of Titanium Alloy.

This study measured optical properties, such as specular, diffuse, and total reflection for 808 nm wavelength, characteristic for high power diode lasers radiation, from the surface of titanium alloy Ti6Al4V at delivery conditions, polished, and oxidized. Moreover, the optical properties of surface layers produced by high power direct diode laser (HPDDL) melting and nitriding were determined. Additionally, a methodology for determining the value of absorption for 808 nm wavelength of the HPDDL radiation on the surface of a melt pool during laser surface melting and nitriding of titanium alloy was proposed. The results show that the distinct differences in absorption affect the heat transfer, thermal conditions of laser heating and thereby the penetration depth during laser melting and nitriding of the titanium alloy.

Block Copolymer Self-Assembly Directed Hierarchically Structured Materials from Nonequilibrium Transient Laser Heating

We highlight two recent approaches operating far from equilibrium for the synthesis of hierarchical porous thin film materials by coupling block copolymer-directed self-assembly with transient laser heating. In first block copolymer-induced writing by transient heating experiments, or B-WRITE, an all-organic block copolymer–resols hybrid film is heated by submillisecond carbon dioxide laser irradiation, directly generating 3D mesoporous continuous resin structures and shapes. Harnessing the highly unique resin materials properties under laser heating conditions, in the second approach block copolymer-directed resin templating is coupled with nanosecond pulsed excimer laser annealing to generate complementary crystalline silicon nanostructures. The underlying structure formation mechanisms for such laser-induced organic and inorganic nanostructured materials are discussed, emphasizing that the nonequilibrium nature of these transient laser annealing approaches opens up vast and new processing windows beyon...

Laser beam shaping for modification of materials with ferritic-martensitic structure

A identify conditions of laser heating for warm forming of materials with a ferritic-martensitic structure was performed. The laser source was a fiber laser with maximum output power of 1500 W. The beam was transformed to an elliptical ring with use a plano-convex lens and axicon. Study of the microstructure allowed revealing fibrous structure of metal, formed during the manufacture of blanks by rolling. Place of plastic deformation is characterized by a local decrease the thickness profile. To eliminate of this defect, is advisable to use the diffractive optical elements, which redistribute the power density of a laser beam.

Formation of surface layer in metal matrix composite A359/20SiCP during laser assisted turning

This paper presents the study on the formation of surface layer in A359/20SiCP metal matrix composite (MMC) during laser assisted turning, with the consideration of SiC particles’ sedimentation in a liquid matrix. The developed model includes the effect of gravity, buoyancy, resistive force of liquid matrix and centrifugal force of the rotating work material. On the basis of the proposed approach the instantaneous sedimentation speed, as well as the depth of sedimented SiC particles are calculated. Consequently, the applied model enables the selection of the effective depth of cut and tool’s angular distance from the laser beam, which can improve the machined surface quality and composite’s exploitation properties. The experiments confirm that sedimentation phenomenon plays an important role during the surface layer formation in laser heating conditions. Furthermore, the laser assisted turning with the selection of the recommended cutting conditions affects the improvement of surface quality, and composite’s wear resistance.

Laser Assisted Milling of Ti-6Al-4V ELI with the Analysis of Surface Integrity and its Economics

This study presents the experimental evaluation of laser assisted milling (LAML) of Ti-6AL-4V ELI (Ti-64), which is used in the orthopedic industry, by using localized preheating of the workpiece via laser irradiation. Improvements to the machinability of this material with LAML are assessed while considering the surface integrity. Suitable laser heating conditions as well as machining conditions are deter- mined based on temperature prediction modeling. Machinability improvements are shown in terms of tool wear, material removal rates and cutting force reduction. Systematic characterization of samples is shown to demonstrate that the machined sub-surfaces are not adversely affected during LAML by precisely controlling laser heating, via hardness measurements, scanning electron microscopy (SEM) for micro- structure analysis, and X-ray diffraction (XRD) for residual stresses. An economic analysis shows that LAML provides the cost reduction over conventional machining.

Laser-Heating Characteristics of CuO-Incorporating Glasses

Laser sealing with glass frits appears a promising technology for sealing various electronic devices (e.g., solar cells, displays) due to its several advantages. The purpose of this study is to understand the relationship between the composition of glasses and their laser-heating conditions. To allow glass to be sealed using laser heating, CuO was added to two different glass systems, in different amounts. The optical absorptivity of the glass samples was related directly to their CuO content. The laser-heating temperature and the CuO content exhibited a proportional relationship. Furthermore, the heating temperature increased linearly with the laser power used. From these results, we could determine the appropriate laser-heating conditions and CuO content for sealing electronic devices using laser-sealing technology.

Lubricant reflow after laser heating in heat assisted magnetic recording

In heat assisted magnetic recording (HAMR) technology for hard disk drives, the media will be heated to about 500 °C during the writing process in order to reduce its magnetic coercivity and thus allow data writing with the magnetic head transducers. The traditional lubricants such as Z-dol and Z-tetraol may not be able to perform in such harsh heating conditions due to evaporation, decomposition and thermal depletion. However, some of the lubricant depletion can be recovered due to reflow after a period of time, which can help to reduce the chance of head disk interface failure. In this study, experiments of lubricant thermal depletion and reflow were performed using a HAMR test stage for a Z-tetraol type lubricant. Various lubricant depletion profiles were generated using different laser heating conditions. The lubricant reflow process after thermal depletion was monitored by use of an optical surface analyzer. In addition, a continuum based lubrication model was developed to simulate the lubricant reflow process. Reasonably good agreement between simulations and experiments was achieved.

Experimental Study of Lubricant Depletion in Heat-Assisted Magnetic Recording: Effect of the Duration of One Laser Heating

Heat-assisted magnetic recording (HAMR) is a technique to overcome the superparamagnetic limit and enabling large increases in the storage density of hard disk drives. The performance of lubricant on disk surface under the high temperature in the heating assisted writing process is a big concern. Laser heating in HAMR is quite different from conventional slow heating. Laser heating duration in one heating and cooling process in HAMR is as short as 1 ns. It is believed that lubricant depletion caused by the nano-second pulse laser heating in HAMR is much less severe than that caused by long time continuous laser heating. In this study, a method to compare the laser heating temperature at different laser heating conditions is developed. Lubricant depletion caused by nano-second and continuous laser heating in one heating and cooling cycle in HAMR is determined quantitatively based on test results. It is found that laser heating duration in one heating and cooling cycle in HAMR is not important to lubricant depletion. No matter laser heating is in nano-second or continuous in one heating and cooling cycle, lubricant depletion caused by the laser heating is comparable provided that the laser heating temperature is comparable.

Thermal Stability of Ultrathin Amorphous Carbon Films for Energy-Assisted Magnetic Recording

Energy-assisted magnetic recording (EAMR) uses a laser-optical system integrated into the magnetic head to heat locally a fine-grained material of high magnetic anisotropy energy density above its Curie temperature, and store single bits in very small areas without being limited by the superparamagnetic effect. However, localized laser heating may affect the thermal stability of the carbon overcoat of the hard disk. To examine the effect of laser heating on the overcoat thermal stability, ultrathin amorphous carbon (a-C) films of similar thickness (~ 3.6 nm) synthesized by filtered cathodic vacuum arc (FCVA) and chemical vapor deposition (CVD) were subjected to repetitive heating under different laser powers. Carbon hybridization and surface roughness of the a-C films were examined by Raman spectroscopy and atomic force microscopy, respectively. For the laser power range studied (150-300 mW), a-C films produced by the FCVA technique demonstrated superior thermal stability than CVD films of similar thickness. To investigate the possibility of further reducing the magnetic spacing, thinner (~ 0.9 nm) a-C films deposited by the FCVA method were subjected to the same laser heating conditions. Although the thermal stability of the FCVA-synthesized a-C films exhibited thickness dependence, even the thinner (~ 0.9 nm) FCVA film demonstrated higher thermal stability than the much thicker (~ 3.6 nm) CVD film. The results of this study illustrate the high potential of FCVA as a coating method for EAMR.

Analysis of hardening of blade tools from steel 40Kh13 under conditions of laser heating

The possibility of effective surface hardening of articles due to the use of highly concentrated energy fluxes is considered with allowance for the effect of the arising thermal stresses on the changes in the temperature range of austenitic transformation. The determined dependences of hardness on the power density and on the rate of the treatment are used to show the possibility of attaining high hardness due to heating to a temperature 150 – 200 K lower than the melting point.

Analysis of microstructural relaxation phenomena in laser-modified fused silica using confocal Raman microscopy

Fused-silica microstructural changes associated with localized 10.6 microm CO(2) laser heating are reported. Spatially resolved shifts in the high-frequency asymmetric stretch transverse-optic phonon mode of SiO(2) were measured using confocal Raman microscopy, allowing construction of axial fictive temperature (T(f)) maps for various laser-heating conditions. A Fourier conduction-based finite-element model was employed to compute on-axis temperature-time histories, and, in conjunction with a Tool-Narayanaswamy form for structural relaxation, used to fit T(f)(z) profiles to extract relaxation parameters. Good agreement between the calculated and measured T(f) was found, yielding reasonable values for relaxation time and activation enthalpy in the laser-modified silica.

Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica

Nano- to micrometer-sized surface defects on UV-grade fused silica surfaces are known to be effectively smoothed through the use of high-temperature localized CO 2 laser heating, thereby enhancing optical properties. However, the details of the mass transport and the effect of hydroxyl content on the laser smoothing of defective silica at sub-micron length scales are still not completely understood. In this study, we examine the morphological evolution of sub-micron, dry-etched periodic surface structures on type II and type III SiO 2 substrates under 10.6 μm CO 2 laser irradiation using atomic force microscopy (AFM). In situ thermal imaging was used to map the transient temperature field across the heated region, allowing assessment of the T-dependent mass transport mechanisms under different laser-heating conditions. Computational fluid dynamics simulations correlated well with experimental results, and showed that for large effective capillary numbers ( N c > 2), surface diffusion is negligible and smoothing is dictated by capillary action, despite the relatively small spatial scales studied here. Extracted viscosity values over 1700–2000 K were higher than the predicted bulk values, but were consistent with the surface depletion of OH groups, which was confirmed using confocal Raman microscopy.

Optical characteristics of cartilage at a wavelength of 1560 nm and their dynamic behavior under laser heating conditions

A double-integrating-sphere system was used to measure the diffuse transmittance, diffuse reflectance, and collimated transmittance of cartilage and polyacrylamide hydrogel samples as a function of temperature under 1560-nm laser heating conditions. The dynamic behavior of the absorption and scattering coefficients and scattering anisotropy of the biomaterials was calculated by the inverse Monte Carlo method. The absorption coefficient of the cartilage and hydrogel samples proved to be linear in temperature. Raising the temperature of the cartilage samples to 80°C caused their absorption coefficient to decrease by some 25%. The temperature-induced change of the absorption spectrum of the interstitial water was found to be responsible for the clarification of the cartilage tissue observed to occur under 1560-nm laser heating conditions. The temperature field produced in the tissue by the laser energy deposited therein was calculated using a bioheat transfer equation with temperature-dependent parameters. The calculation results demonstrated that the temperature-induced changes of the optical parameters of biological tissues should be taken into account to make their 1560-nm laser treatment effective and safe.

The effect of uniaxial tension on the stability of collagen fibers under the conditions of nonuniform laser heating

Collagen degradation caused by IR laser irradiation in ligament tissues was studied by thermal analysis and cross-polarization optical coherent tomography. It was found that, at 60°C, laser-induced modification of the quasi-crystalline packing of ordered collagen fibers occurred without the helix-coil molecular conformation transition. It was shown that, for uniaxial tension of ligaments, laser irradiation caused serious distortions in the structure of collagen and increased the fraction of macromolecules in the random coil state. It was assumed that the thermomechanical effect of laser treatment during laser heating played an important role.