Laser Heating Research Articles

Decoupling Carrier Dynamics and Energy Transport in Ultrafast Near-Field Nanoscopy.

Ultrafast near-field optical nanoscopy has emerged as a powerful platform to characterize low-dimensional materials. While analytical and numerical models have been established to account for photoexcited carrier dynamics, quantitative evaluation of the associated pulsed laser heating remains elusive. Here, we decouple the photocarrier density and temperature increase in near-field nanoscopy by integrating the two-temperature model (TTM) with finite-difference time-domain (FDTD) simulations. These results reveal that the electron-phonon coupling in a silicon film after femtosecond laser excitation is most pronounced within approximately 3 ps─substantially shorter than the photocarrier decay time scale at tens of picoseconds. Moreover, the coupled TTM-FDTD method indicates that ultrafast laser heating can cause up to a 14% variation in the near-field signal at a 220 μJ/cm2 pump pulse fluence. Our numerical results are further validated by transient experiments, highlighting the potential of this method for investigations of carrier and thermal phenomena in emerging nanomaterials and nanodevices.

Predictive Modeling of Laser Metal Deposition with Moving Mesh Theory: Impact of Secondary Laser Heat Sources on Track Morphology

Predictive Modeling of Laser Metal Deposition with Moving Mesh Theory: Impact of Secondary Laser Heat Sources on Track Morphology

Effect of concentration of aqueous alcohol solution and layer thickness on free convection due to local heating

This paper investigates the effect of point heating, ethyl alcohol concentration, and layer thickness on the convective behavior of the solution. Laser heating enhances heat and mass transfer at low energy costs. For the first time, the research determines boundaries of the transition to the chaotic behavior of the velocity field at a change in several parameters: the initial alcohol concentration and the initial thickness of the liquid layer. Simple estimated ratios are obtained to determine the critical value of the Bond number in a binary solution. The solution behavior is predominantly influenced by the solute Rayleigh and Marangoni numbers. A small alcohol concentration (about 10%) is shown to have a stabilizing effect on the velocity field. In the course of evolution, several flow patterns change sequentially, which is associated with changes in the gradient of surface tension, solution concentration and layer thickness with evaporation time.

Thermomechanical response of biological tissues to sudden temperature rise induced by laser beam: insights from three-phase lag theory

Abstract The laser irradiation of living tissues poses a risk of thermal damage, making it a critical factor in medical procedures such as laser surgery and thermal therapies. Effectively predicting and managing this damage, particularly in hyperthermia therapy, is essential for maximizing treatment efficacy while protecting surrounding healthy tissues. In this context, theoretical and computational models of biological heat transfer, especially the enhanced Pennes bioheat transport equation, have attracted significant research interest. This study contributes to the field by providing a novel analytical solution to the refined Pennes bioheat model, incorporating the three-phase lag (TPL) concept. The research examines heat transfer in a one-dimensional region, where the outer surface is exposed to laser heating while the inner surface remains thermally insulated. It explores the mechanical effects of thermal shock induced by laser treatment, focusing on heat generation patterns across different laser intensities in diseased human skin tissues. To validate the model, numerical inverse and Laplace transform techniques were applied, producing results consistent with existing literature. The findings not only advance the theoretical understanding of bioheat transfer but also enhance the safety and effectiveness of laser-based medical therapies.

Effect of Laser Energy on Anisotropic Material Properties of a Novel Austenitic Stainless Steel with a Fine-Grained Microstructure

Laser powder bed fusion (LPBF) provides a novel approach with high complexity and freedom for material processing and design, and its special thermal history endows the material with anisotropic properties. By adding micro-alloying elements Nb and Ti into conventional 316L, the anisotropy of the novel austenitic stainless steel fabricated by LPBF, which is related to the laser heat input, was investigated. The refined microstructure of this steel was further strengthened with in situ-generated Nb-, Cr-, and Ti-rich nanoprecipitates at a specific location. The heat input affects the material anisotropy, and a lower heat input leads to stronger anisotropy in this steel. The as-built parts at a low heat input in the horizontal and vertical planes exhibited finer microstructures compared to those fabricated at a high heat input. The epitaxial growth of the grains associated with the thermal gradient resulted in the vertical-section grain size being generally larger than that of the horizontal section. As a result, the low-heat-input parts with a finer grain are also stronger in the horizontal direction, with yield and tensile strengths approaching 0.9 and 1.2 GPa, respectively. Meanwhile, the microstructural changes due to the high heat input imparted a better ductility of parts in different sections (a 3.15% and 4.4% increase in the horizontal and vertical directions, respectively). Its mechanical properties depend mainly on the direction of stress coupled with intergranular friction during deformation in both coarse and fine grains.

Modification of the Surface Layer of Grey Cast Iron by Laser Heat Treatment

This paper presents possible modifications to the properties of grey cast iron by laser heat treatment. These modifications are analyzed especially with regard to wear properties as a result of graphite content, which is a well-known solid lubricant. Examples of applications of grey cast iron in cases where good wear resistance is required are presented. Laser hardening from the solid state, laser remelting, and laser alloying are characterized. In this study, changes in the surface layer caused by these treatments were analyzed (especially the influence on the microstructure—including graphite content—and wear properties). It was shown that all of these treatments enable the wear resistance of the surface layer to be enhanced, mostly due to the increase in the hardness and microstructure homogeneity. It was also proven that it is possible to retain the graphite phase (at least partially) in the modified surface layer, which is crucial in the case of friction wear resistance. In particular, laser hardening from the solid state does not eliminate graphite. Laser remelting and alloying cause the dilution of carbon from the graphite phase to the melted metal matrix, but, in the case of nodular cast iron, it is possible that not all of the valuable graphite in the surface layer is lost.

Liquid Structure of Magnesium Aluminates.

Magnesium aluminates (MgO)x(Al2O3)1-x belong to a class of refractory materials with important applications in glass and glass-ceramic technologies. Typically, these materials are fabricated from high-temperature molten phases. However, due to the difficulties in making measurements at very high temperatures, information on liquid-state structure and properties is limited. In this work, we employed the method of aerodynamic levitation with CO2 laser heating at large scale facilities to study the structure of liquid magnesium aluminates in the system (MgO)x(Al2O3)1-x, with x = 0.33, 0.5, and 0.75, using X-ray and neutron diffraction. We determined the structure factors and corresponding pair distribution functions, providing detailed information on the short-range structural order in the liquid state. The local structures were similar across the range of compositions studied, with average coordination numbers of n¯AlO∼4.5 and n¯MgO∼5.1 and interatomic distances of rAlO=1.76-1.78 Å and rMgO=1.93-1.95 Å. The results are in good agreement with previous molecular dynamics simulations. For the spinel endmember MgAl2O4 (x = 0.5), the average Mg-O and Al-O coordination numbers gave rise to conflicting values for the inversion coefficient χ, indicating that the structural formula used to describe the solid-state order-disorder transition is not applicable in the liquid state.

Numerical modelling and simulation studies of laser beam heating parameters on depth of cut and surface temperature in laser-assisted machining of Ti6Al4V

Laser-assisted machining (LAM) is a hybrid machining process which uses a laser heat source to heat the narrow zone of a work part material ahead of the cutting tool. Surface temperature and heat-affected depth (effective depth of cut) achieved during localised laser heating play an important role in the machinability of the workpiece. In the current work, moving laser heat source simulation studies are performed using COMSOL Multiphysics software. The effect of laser power, beam diameter, scan speed, convective heat transfer coefficient and absorptivity are studied by simulating different test cases. Results show that the average maximum surface temperature increases when the laser power is increased from 100 W to 160 W by 55%. It increases with the increase in absorptivity from 0.3 to 0.39 by 18%. The average maximum surface temperature decreases when the laser diameter is increased from 1 to 2.5 mm by 46%. It decreases with the increase in scan speed from 50 to 200 mm/min by 5%. In the case of effective depth of cut, similar trends were observed with the variation of the above parameters. Further, the variation of convective heat transfer coefficient from 5 to 20 W/m-K does not affect the average maximum surface temperature and effective depth of cut. It was found that the laser power has a significant effect on average maximum surface temperature and effective depth of cut compared to other parameters.

Laser melting, evaporation, and fragmentation of nanoparticles: Experiments, modeling, and applications

This review examines the processes of laser heating, melting, evaporation, fragmentation, and breakdown of metal nanoparticles, as well as the dependences and values of the threshold laser parameters that initiate these processes. Literature results are analyzed from experimental studies of these processes with gold, silver, and other nanoparticles, including laser surface melting and evaporation of nanoparticles and Coulomb fragmentation of nanoparticles by ultrashort laser pulses. A theoretical model and description of the thermal mechanisms of mentioned processes with metal (solid) nanoparticles in a liquid (solid) medium, initiated by the action of laser pulses with the threshold fluences, are presented. Comparison of the obtained results with experimental data confirms the accuracy of the model and makes it possible to use them to evaluate the parameters of laser thermal processing of nanoparticles. Applications of the processes include the laser melting, reshaping, and fragmentation of nanoparticles, the formation of nanostructures and nanonetworks, the laser processing of nanoparticles located on substrates, and their cladding on surfaces in various laser nanotechnologies. The use of laser ignition, combustion, and incandescence of nanoparticles is discussed, as is the use of nanoparticle-triggered laser breakdown for spectroscopy. These laser processes are used in photothermal nanotechnologies, nanoenergy, laser processing of nanoparticles, nonlinear optical devices, high-temperature material science, etc. In general, this review presents a modern picture of the state of laser technology and high-temperature processes with nanoparticles and their applications, being focused on the latest publications with an emphasis on recent results from 2021–2024.

Analysis of temperature changes in living tissue using the modified fractional thermal conduction model under laser heat flux on the skin surface

Analysis of temperature changes in living tissue using the modified fractional thermal conduction model under laser heat flux on the skin surface

Laser-induced adhesives with excellent adhesion enhancement and reduction capabilities for transfer printing of microchips.

Transfer printing based on tunable and reversible adhesive that enables the heterogeneous integration of materials is essential for developing envisioned electronic systems. An adhesive with both adhesion enhancement and reduction capabilities in a rapid and selective manner is challenging. Here, we report a laser-induced adhesive, featuring a geometrically simple shape memory polymer layer on a glass backing, with excellent adhesion modulation capability for programmable pickup and noncontact printing of microchips. Selective and rapid laser heating substantially enhances the adhesive's adhesion strength from kilopascal to megapascal within 10 ms due to the shape fixing effect, allowing for precise and programmable pickup. Conversely, the enhanced adhesion can be quickly reduced and eliminated within 3 ms through the shape recovery effect, enabling noncontact printing. Demonstrations of transfer printing microlight-emitting diodes (LEDs) and mini-LEDs onto various low-adhesive flat, rough, and curved surfaces highlight the unusual capabilities of this adhesive for deterministic assembly.

Ultrasonic Surface Finishing of AISI 1045 Steel Hardened by Laser Heat Treatment with Fibre Laser and Scanning Optics: Layered-Structure-Induced Hardening and Enhanced Surface Morphology

Ultrasonic Surface Finishing of AISI 1045 Steel Hardened by Laser Heat Treatment with Fibre Laser and Scanning Optics: Layered-Structure-Induced Hardening and Enhanced Surface Morphology

Piezothermoelastic interaction in piezoelectric rods induced by a timed laser pulse without energy dissipation

The main aim of this article is to study the piezo-thermoelastic interaction in piezoelectric rods without energy dissipation due to a laser heat source with a timed pulse. Laplace transforms are used to represent the analytical solutions in the transformations domain. The governing equations of piezo-thermoelasticity in the Green and Naghdi model (GNII model without energy dissipation) in the presence of a laser heat source with a timed pulse are solved exactly in the Laplace domain, calculating the temperature, the stress, the displacement, and the electric potential. Numerical Laplace inversion is then used to find the general solution of the variables under study, which are then graphically shown.

Transient behavior of thermocapillary convection in thin liquid film exposed to step laser heating

Temporally developing thermocapillary convection induced by step laser heating of a thin liquid film has been studied numerically. Computations are performed using the commercial software STAR CCM+ version 2022.1. The liquid film of silicone oil (high Prandtl number fluid) is 60 mm in diameter and 3 mm in thickness. Flow characteristics related to surface velocity and surface temperature have been studied. Validation of the computations is achieved for the surface velocity, the velocity along thickness and the surface temperature through comparison with PIV and IR camera measurements. The laser-beam with a carbon dioxide gas laser (10.4 μm in wavelength) is used for heating. It is found that the temporally developing profile of surface velocity shows two local velocity peaks (uS1 and uS2) at two radial locations (rS1 and rS2) respectively. The first peak, uS1, appearing due to the steep temperature gradient generated by laser-beam heating and its radial position, rS1, do not change noticeably with time. On the other hand, the second peak, uS2, travels radially outwards with decreasing magnitude in a self-propelling manner until its radial position, rS2, approaches an asymptotic maximum. Detailed analysis of the coupling among radial temperature gradient, local pressure variation and local convective acceleration near the second peak reveals that hydrothermal mechanisms are responsible for self-propelling travel of uS2. The transient behaviors of both primary and secondary velocity peaks are found to depend on the fluid viscosity and the laser-beam settings

Photothermally‐Engineered Crystallization of GAP‐Se Bulk Chalcogenide Nanocomposites toward the Realization of 3D Gradient Refractive Index Profiles

AbstractTailorability of a medium's optical properties, specifically refractive index and dispersion, is key to enabling compact optical designs. Chalcogenide glasses (ChGs) are widely used for infrared (IR) imaging applications, and the development of gradient refractive index (GRIN) optics. This work extends efforts to create and characterize 3D GRIN profiles in bulk multi‐component Ge‐As‐Pb‐Se (GAP‐Se) ChGs through spatially selective conversion of commercial glass to glass ceramic. This work extends prior efforts on bulk and film lab‐scale glass media, to that of a commercially produced material with improved optical homogeneity. Laser‐induced crystallization upon heat treatment results in the formation of high index Pb‐containing crystals that contribute to an increase in the nanocomposite's resulting effective refractive index, neff. The material's induced crystallinity imparted via laser exposure and heat treatment using metrology tools such as refractometry, X‐ray diffraction, FTIR, and TEM are studied. The resulting material response is quantified which is shown to be modulated via laser dose in both lateral and for the first time, axial directions enabling the first demonstration of a true, 3D GRIN profile. By comparing these outcomes to prior radial GRIN structures, the promise of these media as candidate materials for infrared systems.

Plasmonic photothermal photodynamic therapy in mice with colorectal cancer

The need for searching for new methods of antitumor therapy is due to the sharp increase in morbidity and mortality from cancer, as well as because of the fact that conventional chemo- and radiotherapy are often insufficiently effective owing to the development of tumor cells resistance. Plasmonic photothermal therapy (PPT) is a method based on tumor hyperthermia by laser heating of metal nanoparticles with plasmon resonance properties.

Balanced truncation model reduction for laser heating wafer model in frequency restricted domain

Modeling and simulating laser heating phenomena are crucial for optimizing manufacturing processes and ensuring high-quality final products. A major challenge in semiconductor manufacturing is achieving accurate, real-time temperature control during wafer heating. To reduce the computational burden of complex mathematical models, low-dimensional reduced models can be employed. In this paper, we develop a mathematical model for laser heating in silicon wafers. For model reduction, we use the balanced truncation method, considering both frequency-unrestricted and restricted cases. Additionally, the rational Krylov subspace method is applied to solve high-dimensional sparse matrix equations. To gain key physical insights, we use the COMSOL Multiphysics package. Finally, some numerical experiments are conducted using MATLAB to validate the proposed approach.

Sensitivity Improvement of Electrochemical Virus Detection through Morphology Control of CNT Electrodes

The global pandemic of influenza virus (IFV) and Covid-19 has created a strong need for the technology to measure viruses quickly and sensitively. Currently, PCR-based detection technology is used to accurately detect these viruses, however they lack immediacy as it takes several days for the viruses to grow to detectable amounts. A complementary method that allows immediate detection is an antigen testing that uses complementary substances (aptamers and antibodies) that specifically bind to target virus. Among them, electrochemical detection via cyclic voltammetry is being researched as a method that can measure target virus in solutions with high sensitivity and high speed. Since these utilize chemical reactions on the electrode surface, the material and surface morphology of the electrode are important factors that govern sensitivity. Previous research has reported that highly sensitive and robust virus testing can be performed by using carbon nanotube (CNT) films, which are chemically stable and have a large surface area, as chemical electrodes. However, the effect of the surface morphology of CNT films such as structures and defects has not been sufficiently studied.In this study, we attempted to increase the sensitivity of electrochemical virus testing by controlling the surface morphology of CNT films and increasing the amount of aptamer adsorption. The morphology of the CNT film was controlled through heat and non-heat laser processing by using 532 nm nano-second and/or pico-second pulsed lasers. The fabricated morphology was evaluated by SEM and polarized Raman spectroscopy. In addition to measuring the amount of aptamer adsorption for each morphology using ultraviolet spectroscopy, we also evaluated the detection sensitivity of IFV when using the CNT films as an electrochemical electrode. As a result, we achieved the high sensitivity and reliability IFV detection with fg/ml of the limit of detection. In the presentation, we will introduce the developed CNT morphology control technology and discuss the relationship between morphology and aptamer adsorption amount. Figure 1

Degradation and Safety Analysis of Large Format LiFePO4/Graphite Battery

Large format LiFePO4/Graphite (LFP/Gr) Lithium-ion battery (LIB) have been developed for electric vehicles (EV) and stationary use. In case of large surface electrodes, intrinsic two-phase reaction of LFP has a risk to induce inhomogeneous reaction in planar electrode surface. We applied >200 Ah class LFP/Gr LIBs and cycled them around 80-65 % SOH levels. Among them, we applied non-destructive differential voltage analysis (dV/dQ) to three cells (Cell1:SOH 80.9 %, Cell2:SOH 73.5 %, Cell3:SOH 68.4 %), and determined the degree of inhomogeneity of the electrodes by disassembly of the cell in the Ar-filled glove box.We could obtain dV/dQ peak corresponds to Gr 2nd stage single phase by charge curve analysis between SOC 0 and 100 % at C/20. Based on the assumption that Gr capacity is twice of the Gr 2nd stage peak capacity, Gr capacity was sufficiently larger than cell capacity. Therefore, cell capacity fade was not related to the capacity fade of Gr but caused by the shift of the cathode / anode operation window (SOW) due to loss of lithium inventory (LLI) and/or capacity fade of LFP.After dV/dQ analysis with capacity check, cells were disassembled at 2.5 V, and confirmed LFP and Gr capacity by reassembling coin cells with Li counter electrode. Reassembled LFP/Li cells was discharged to 2 V, and Gr/Li cells were deintercalated to 2.5 V. The subtracted value of these residual capacities, we could estimate SOW capacity. The obtained estimated cell capacity by LFP-SOW showed strong correlation with SOH of cells before disassembly (R=0.98). Therefore, we confirmed that capacity fade of the cell was due to increase in SOW and/or capacity fade of LFP.To determine the degree of inhomogeneity in electrode planar, we applied XRD to LFP. As LFP reaction proceeds typical two-phase reaction, we can indirectly estimate Li content by estimating ratio of LFP and FePO4(FP). The LFP/FP ratio was optimized by Rietveld refinement of the diffraction peaks in various sampling points of the electrode sheet. We confirmed several macroscale inhomogeneous Li distributions in planar LFP electrode. Li poor area was observed at the beginning and the final edge of the roll electrode. The correlation details between cell SOH and degree of inhomogeneity will be discussed in the presentation.In addition, we applied two kinds of abuse test, overcharge and forced internal short circuit test by laser spot heating to three cells with different SOH. In case of overcharge, cell was charged at 0.78 C from SOC 100 %. In case of laser heating, pulse laser with 0.5 sec supply / 0.1 sec rest at 2000 W applied to the cell. The difference of the obtained parameters, and correlation with SOH will be discussed in the presentation.

Using Thermal Crowding to Direct Pattern Formation on the Nanoscale.

Metal films and other metal geometries of nanoscale thickness deposited on an insulating substrate, when exposed to laser irradiation, melt and evolve as fluids as long as their temperature is sufficiently high. This evolution often leads to pattern formation, which may be influenced strongly by material parameters that are temperature dependent. In addition, the laser heat absorption itself depends on the time-dependent metal thickness. Self-consistent modeling of evolving metal films shows that, by controlling the amount and geometry of the deposited metal, one can control the instability development. In particular, we demonstrate the "thermal crowding" effect: additional metal leads to elevated temperatures, which strongly influence the metal evolution, even if the metal geometries are disjoint. We demonstrate that the communication of disjoint metal domains occurs via heat diffusion through the underlying substrate. Fully self-consistent modeling focusing on the dominant effects, as well as accurate time-dependent simulations, allow us to describe the main features of thermal crowding and provide a route to control fluid instabilities and pattern formation on the nanoscale.