Short Pulse Laser Irradiation Research Articles

Self-Organizing Sub-μm Surface Structures Stimulated by Microplasma Generated Reactive Species and Short-Pulsed Laser Irradiation.

Catalysts are critical components for chemical reactions in industrial applications. They are able to optimize selectivity, efficiency, and reaction rates, thus enabling more environmentally friendly processes. This work presents a novel approach to catalyst functionalization for the CO2 reduction reaction by combining the reactive species of an atmospheric pressure plasma jet with the electric fields and energy input of a laser. This leads to both a nanoscale structuring as well as a controllable chemical composition of the surface, which are important parameters for optimizing catalyst performance. The treatment is conducted on thin copper layers deposited by high power pulsed magnetron sputtering on silicon wafers. Because atomic oxygen plays a key role in oxidizing copper, two photon absorption fluorescence is used to investigate the atomic oxygen density in the interaction zone of the COST plasma jet and a copper surface. The used atmospheric pressure plasma jet provides an atomic oxygen density at the surface in a distance of 8 mm to the jet nozzle of approximately or a flux of . Pulsed laser-induced dewetting is used to form nanoparticles from the deposited copper layer to enhance catalytic performance. Varying the layer thickness allows control of the size of the particles. A gas flow directed on the sample during the combined treatment disturbs the particle formation. This can be prevented by increasing the laser energy to compensate for the cooling effect of the gas flow. Investigating the surface using X-ray photoemission spectroscopy reveals that the untreated copper layer surface consists mostly of metallic copper and Cu(I) oxide. Irradiating the sample only with the laser did not change the composition. The combination of plasma and laser treatment is able to produce Cu(II) species such as CuO, whose concentration increases with treatment time. The presented process allows the tuning of the ratio of C2O/CuO, which is an interesting parameter for further studies on copper catalyst performance.

Subpicosecond laser ablation behavior of a magnesium target and crater evolution: Molecular dynamics study and experimental validation

Abstract The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics (MD) simulations and experiments. The simulation results exhibit that the main failure mode of single-crystal Mg film irradiated by a low fluence and long pulse width laser is the ejection of surface atoms, which has laser-induced high stress. However, under high fluence and short pulse width laser irradiation, the main damage mechanism is nucleation fracture caused by stress wave reflection and superposition at the bottom of the film. In addition, Mg[0001] has higher pressure sensitivity and is more prone to ablation than Mg [ 10 1 ¯ 0 ] . The evolution equation of crater depth is established using multi-pulse laser ablation simulation and verified by experiments. The results show that, under multiple pulsed laser irradiation, not only does the crater depth increase linearly with the pulse number, but also the quadratic term and constant term of the fitted crater profile curve increase linearly.

Determination of Laser Parameters in Thermomechanical Treatment of Skin Based on Response Surface Methodology

An investigation was conducted to examine the photothermal and thermomechanical effects of short-pulse laser irradiation on normal tissues. This study analyzed the impact of short-pulse laser radiation on the heat-affected region within tissues, taking into consideration a set of laser variables, namely wavelength, intensity, beam size, and exposure time. The beam size ranged between 0.5 and 3 mm, and the intensity of the laser radiation ranged from 1 to 5 W/mm2 at wavelengths of 532 and 800 nm. A three-layered, three-dimensional model was implemented and studied in a polar coordinate system (r = 10 mm, z = 12 mm) in COMSOL Multiphysics (version 5.4, COMSOL Inc., Stockholm, Sweden) to perform numerical simulations. The Pennes bioheat transfer model, Beer-Lambert, and Hooke’s law are integrated to simulate the coupled biophysics problem. Temperature and stress distributions resulting from laser radiation were produced and analyzed. The accuracy of the developed model was qualitatively verified by comparing temperature and mechanical variations following the variations of laser parameters with relevant studies. The results of Box-Behnken analysis showed that beam size (S) had no significant impact on the response variables, with p-values exceeding 0.05. Temperature (Tmax) demonstrates sensitivity to both beam intensity (I) and exposure time (T), jointly contributing to 89.6% of the observed variation. Conversely, while beam size (S) has no significant effect on stress value (Smax), wavelength (W), beam intensity (I), and exposure time (T) collectively account for 71.6% of the observed variation in Smax. It is recommended to use this model to obtain the optimal values of the laser treatment corresponding to tissue with specified dimensions and properties.

Thermal relaxation parameters estimation of non-Fourier heat transfer in laser-irradiated living tissue using the Levenberg-Marquardt algorithm

The present work is concerned with solving the inverse heat transfer problem (IHTP) to estimate the thermal relaxation parameters corresponding to the dual phase lag (DPL) model-based bio-heat transfer in laser-irradiated living tissue. This problem is divided into two parts: direct and inverse problems. The solution of the inverse problem has been obtained using the Levenberg–Marquardt algorithm. On the other hand, the solution to the direct problem is obtained by solving the DPL model-based bio-heat transfer equation (BHTE) with the transient radiative transfer equation (TRTE). So, the TRTE has been numerically solved by the modified discrete ordinate method (DOM) to find the intensity field in the living tissue subjected to short-pulsed laser radiation, and it acts as a heat source in the DPL model-based BHTE. So, the DPL model-based BHTE has been analytically solved by employing the finite integral transform technique to get the temperature variation inside the laser-irradiated living tissue. First, the computer code developed for estimating unknown thermal relaxation parameters using the Levenberg–Marquardt algorithm has been verified against the data given in the literature, and found good agreement between them. Then, the thermal response of laser-irradiated living tissue has been investigated. After that, the influence of sensor position on the sensitivity of the IHTP solution has been discussed. The impact of the total transient readings and the measurement error on estimating the unknown parameters have been investigated. The present study’s findings can significantly contribute to various parameter estimation problems where the conventional methods for direct measurements of parameters are impossible or very difficult. Furthermore, the current results may considerably impact the study of the thermic response of living tissue during laser-based photothermal therapy.

Modification of Diamond Surface by Femtosecond Laser Pulses

The basic mechanisms of laser interaction with synthetic diamond are reviewed. The characteristics of the main regimes of diamond surface etching are considered. In addition to the well-known graphitization and ablation processes, nanoablation and accumulative graphitization, which have attracted relatively recent attention, are described in detail. The focus is on femtosecond (fs) laser exposure, which allows for the formation of a dense cold electron–hole plasma in the focal zone and minimal overheating in the surrounding area. This potentially opens the way to the development of unique laser-based technologies that combine physical and chemical processes for precise surface treatment and functionalization. The physical limitations that determine how precisely the diamond surface can be treated by short-pulsed laser radiation and possible ways to overcome them with the ultimate goal of removing ultrathin layers of the material are discussed. Special attention is paid to the novel possibility of inducing the local formation of point active defects—nitrogen vacancy (NV) complexes in the laser-irradiated zone. Such defects have been at the forefront of solid-state physics for the past thirty years due to continuous attempts to exploit their unique properties in quantum optics, quantum computing, magnetometry, probing, and other fields. Both regimes of NV center formation with and without graphitization of the diamond lattice are considered. Thus, it is shown that intense pulsed laser irradiation is a perfect tool for the processing of synthetic diamonds at the micro-, nano-, and even at the atomic level, which can be well controlled and managed.

An inversion approach for non-invasive detection of subcutaneous structure and temperature based on 1D residual neural network

Laser skin dermatology has attracted increasing attention with awareness of the aesthetic sense. Real-time detection of subcutaneous vessel temperature and structure during laser treatment is essential for efficacy and safety of surgery. By using 1D residual neural network to improve the accuracy of feature extraction, an inverse method model with outstanding reconstruction performance and noise insensitivity was proposed to estimate vascular parameters including temperature, depth and diameter of blood vessel. The network established an end-to-end mapping of the time-dependent skin surface temperature after short-pulse laser irradiation to the temperature gradient along the skin depth, allowing vascular parameters to be extracted directly from the observed data measured by the infrared camera. The model trained by data containing noise of multiple intensities could identify and attenuate noise in the original data, which is beneficial to suppress the broadening effect of a significant broadening of reconstructed temperature peaks induced by noise and significantly improve the reconstruction accuracy of less than 5%. In comparison with traditional iterative methods, the new model shows technical superiority in its unparalleled accuracy and low computational cost as well as great potential for real-time monitoring of subcutaneous vascular features.

Heat transport across multi-layered skin tissue experiencing short-pulse laser irradiation: Case of temperature-dependent thermal physical parameters

Exactly tracing the heat transport within a multi-layered biological tissues exposed to a pulse laser irradiation is the key issue for successful application of modern therapies. The purpose of this paper is to explore the heat transport within an irradiated biological tissue with multi-layered sub-structure and temperature-dependent physical properties. A non-linear model of bio-heat transfer involved variable physical properties with respected to the space and temperature has been firstly proposed on the basis of dual-phase-lag model (DPL) of bio-heat transfer. A numerical procedure constructed on an explicit difference algorithm is then developed to trace the temperature history of each layer with temperature-dependent physical properties and associated thermal damage induced by a pulse laser. The parametric study of laser parameters, structure parameters of tissue and blood vessel, and variable thermal parameters on thermal response has been performed. The results state that the heat transport has been inhibited when considering temperature-dependent physical properties and a lower temperature would be predicted, which also would weaken the underlying thermal damage.

CHARACTERISTICS OF GLASSES IN PRODUCTS OF EXPERIMENTAL MODELING OF IMPACT MELTS

The transformation of substances under extremely high pressures and temperatures is an actual direction both in the field of solid state physics and materials science, and for natural objects. Among the latter, the most interesting are ultrahigh-pressure high-temperature glasses recently found at the Kara giant meteorite crater (Pai-Khoi, Russia), formed from impact melts at pressure about 60 – 80 GPa and the temperature range of 2300 – 2500 °C. These glasses are characterized by unusual structural and phase state features that require deeper study to clarify their physical properties and the possibility of using them as prototypes of innovative materials. Experimental modeling of the impact process in laboratory conditions allows to identify the nature of phase transformations during impactogenesis. Here the modeling of the impact process has been carried out by short-pulse laser radiation (0.5 ms) on the example of clay-containing siltstones and limestones with and carbonaceous components. The impact glasses have been produced from aluminosilicate and quartz components of the host target rocks of the Kara target under pressure conditions ?90 GPa and temperatures ?7000 °C. To study the synthesized products of the impact glasses, high resolution methods have been used – Raman spectroscopy and scanning electron microscopy with microprobe analysis. The provided studies have shown that under the extreme conditions the impact glasses of a specific composition containing a high concentration of Ca and carbon are formed. Thus, the experiments conducted have shown the possibility of obtaining glasses of a wide composition, including carbon-containing glass, which can be used for further studies aiming to develop new materials and technologies of their producing.

An Analytical Solution of the Hyperbolic Bioheat Model of the Cornea Subjected to Laser Irradiation

The thermal effects occurring in a cornea subjected to short-pulsed laser irradiation during laser thermokeratoplasty (LTK) are investigated. The transient bioheat transfer is described by the hyperbolic model and solved analytically using the finite Fourier transform technique and the method of variation of parameters. The computational results predicted by the hyperbolic model show that the degree of damage in the corneal tissue induced by Ho: YAG laser irradiation under LTK surgery increases linearly with time. An increase in the convection coefficient of the anterior corneal surface causes an insignificant reduction in the corneal temperature, whereas an increase in the value of phase lag in the heat flux vector causes a rise in the corneal temperature .

Temporal Evolution of Refractive Index Induced by Short Laser Pulses Accounting for Both Photoacoustic and Photothermal Effects

Materials such as silicon, copper, gold, and aluminum exhibit strong absorption and scattering characterization under short-pulsed laser irradiation. Due to the photoelastic effect and thermoelastic relaxation, the focal area may induce a local modulation in the refractive index, which can be detected with the intensity reflection coefficient perturbation. Normally, the thermal effect causes a weak refractive index change and is negligible, compared with the pressure-induced effect in most photoacoustic analytical systems. In this study, we present a theoretical model with the whole process of absorbed energy conversion analysis for the refractive index perturbation induced by both thermal effect and photoacoustic pressure. In this model, data analysis was carried out on the transformation of the energy absorbed by the sample into heat and stress. To prove the feasibility of this model, numerical simulation was performed for the photothermal and photoacoustic effects under different incident intensities using the finite element method. Experiment results on silicon and carbon fiber verified that the refractive index change induced by the photothermal effect can be detected and be incorporated with pressure-induced refractive index change. The simulation results showed very good agreement with the results of the experiments. The main aim of this study was to further understand the absorption and conversion process of short-pulsed light energy and the resulting photothermal and photoacoustic effects.

Micro-perforation of the diffusion media for polymer electrolyte membrane fuel cells using short and ultrashort laser pulses

The water management within polymer electrolyte membrane fuel cells is one of the main challenges limiting their extensive commercial application. By introducing directed pores in the carbon-based diffusion media, the water transport properties can be improved. Thus, the performance at demanding operating conditions and the lifetime of the fuel cell can be enhanced. In this work, the microporous layer of a diffusion media was perforated by locally ablating material using short and ultrashort-pulsed laser radiation with infrared wavelength. The influence of the pulse duration as well as the peak pulse fluence and the number of pulses on the ablation rate and the surface quality was evaluated. Laser scanning microscopy was applied to assess the topography of the micro-drillings. The heat-affected zone around the micro-drillings was investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The impact of short and ultrashort pulse laser radiation on the hydrophobic binder within the microporous layer was studied. Results showed a decreased binder evaporation in the vicinity of the micro-drillings by a reduction of the pulse length from the nanosecond to the picosecond range.

Thermoelastic modeling of laser-induced generation of strong surface acoustic waves

Short pulse laser irradiation of a substrate can generate pulses of surface acoustic waves (SAWs) capable of propagating long distances along the surface of the irradiated substrate. In this work, we use thermoelastic modeling of the generation of SAWs on a Si substrate to explore the effect of irradiation parameters, i.e., pulse duration, laser spot size, absorption depth, and spatial profile of the laser energy deposition, on the strength of the SAWs. A particular goal of this study is to establish the optimum conditions for maximizing the strength of the surface waves generated in the nonablative, thermoelastic irradiation regime. The simulations demonstrate that the highest strain amplitude of the laser-generated SAWs can be achieved for a laser spot size comparable to the characteristic length of the SAW propagation during the laser pulse. The amplitude of SAWs increases with the increase in the characteristic laser energy deposition depth, and laser pulses with sharper spatial energy deposition profiles (flat-top laser beams) produce stronger SAWs. For the optimal set of irradiation parameters, the strain amplitude of a SAW generated in Si in the thermoelastic regime can reach the levels of 10−4–10−3, which are sufficiently high for causing nonlinear sharpening of the wave profile and the formation of a shock front during the wave propagation from the laser spot. The computational predictions suggest the feasibility of a continuous generation of strong nonlinear pulses of SAWs, which may be utilized for driving the surface processes in thin film deposition, growth of two-dimensional materials, heterogeneous catalysis, and other applications.

Analysis of transient signal broadening of silicon-based photodiodes irradiated by nanosecond laser

To investigate the saturation characteristics of silicon-based optoelectronic devices caused by short-pulse laser irradiation, an Nd:YAG laser with a wavelength of 1064 nm and two typical silicon-based photodiodes, PN and PIN, were employed to build an experimental system to measure the transient response signal of the device. The change. The experimental results demonstrate that with the increase of laser energy density, the nonlinear saturation of the two devices occurs, and the response time is significantly increased. This is a response degradation phenomenon for the response of the device and the signal after the saturation of the two devices. By analyzing the rising edge, half-height width, and bottom width of the characteristic quantity, it can be found that the broadening of the two devices is mainly due to the broadening of the falling edge of the response signal. However, the broadening of the PIN-type photodiode after laser irradiation is compared with that of PN. Type photodiodes remain more remarkable. Through the analysis of carrier dynamics, when the signal is restored, the movement of carriers is affected by a large number of photogenerated carriers after the laser irradiation ends, affecting the drift movement and space charge region during the bipolar transport of carriers. The width of the two devices attenuates the speed when the signals of the two devices are restored, leading to the saturation caused by the laser irradiation of the two devices

Mathematical modeling of short pulsed laser irradiation in the cornea: a dual phase lag model

Journal of Applied Mathematics and Computational Mechanics, Prace Naukowe Instytutu Matematyki i Informatyki, Politechnika Częstochowska, Scientific Research of the Institute of Mathematics and Computer Science, Czestochowa University of Technology

Laser structuring of graphite anodes and NMC cathodes – Proportionate influence on electrode characteristics and cell performance

For this study, microscopic diffusion channels were introduced into graphite anodes and NMC622 cathodes through short-pulsed laser radiation. The impact on the performance of coin cells comprising anodes and cathodes in pristine and structured conditions, respectively, was investigated in a discharge rate test. At high rates (1 C – 3 C), particularly cells with laser-structured anodes showed a significant increase in capacity retention of up to 10 % in comparison to cells with pristine anodes. Characteristic features in the incremental capacities indicated cell polarization and diffusion inhibition as the rate-limiting mechanisms at high discharge rates and revealed differences in the dominating deintercalation stages between the cell configurations. Fitting an equivalent circuit model to the impedance spectra of symmetric cells showed a reduction of the ionic resistances by approx. 45 % for the anodes and approx. 21 % for the cathodes through laser structuring. A similar behavior was observed for the MacMullin numbers and effective tortuosities of the electrodes. In conclusion, laser structuring offers a particular potential to overcome the diffusion-limiting characteristics of the graphite anodes. The insights into the proportionate impact of anode or cathode structuring are of high value for the design and manufacturing of future lithium-ion batteries.

Chemical order relaxation in a substitutional solid alloy around the critical temperature

The relaxation rate for phase transformations depends on how the system is far from its thermodynamic equilibrium. If, for example, temperature in the system approaches to the phase transition point, the relaxation rate becomes close to zero. We theoretically investigate the laser-induced kinetics of chemical order-disorder transformations (CODTs) in substitutional solid alloys at temperatures $T$ satisfying the condition that $|T--{T}_{c}|\phantom{\rule{0.16em}{0ex}}\ensuremath{\ll}\phantom{\rule{0.16em}{0ex}}{T}_{c}$, where ${T}_{c}$ is the CODT critical temperature. In these studies, we use the equation obtained by Metiu, Kitahara, and Ross, that is, $d\ensuremath{\eta}/dt=--(\mathrm{\ensuremath{\Gamma}}/2{k}_{B}T)\ensuremath{\partial}F/\ensuremath{\partial}\ensuremath{\eta}$, where $0<\ensuremath{\eta}<1$ is the chemical order parameter, \ensuremath{\Gamma} is the frequency of atomic jumps, ${k}_{B}$ is the Boltzmann constant, and $F$ is the free energy of the system, which we combine with the Landau theory for second-order phase transitions. If the two lowest terms are retained only in a Taylor expansion of $F$, the $\ensuremath{\eta}(t)$ dependence can be found analytically. Such an approach is assumed to be valid for sufficiently small $\ensuremath{\eta}<0.5$. As an example, we simulate CODTs in the thin-film (40-nm thickness) binary alloy of ${\mathrm{Fe}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}$ ($x=0.6$). Our simulations show that both extensive chemical ordering and disordering in the solid alloy are feasible under short-pulse laser irradiation, at least, at a nanosecond time scale. This finding can be useful for improving the properties of functional alloyed materials and for extension of their potential applications.

Experimental modeling of phase transformations in a weakly ordered carbon substance under impact treatment

The results of experimental modeling of impact transformation of weakly ordered carbon substance by short-pulse laser radiation on glassy carbon are presented. The experiments yielded extremely high temperatures of ~14500 K and pressures of ~300 GPa, which are comparable with temperatures and pressure of the formation of large Earth’s meteorite craters. The analysis of the transformation products of a target substance showed melting of glassy carbon, its further solidifcation, partial crystallization upon cooling and formation of polyphase composites, which contain hexagonal nanocrystalline graphite and hollow onion-like and one- and two-layer fullerene-like structures. The synthetic products, including high-pressure carbon polymers and hollow onionlike multi-layer fullerene-like structures are of interest as carbon materials, which form at ultrahigh pressures and temperatures. The results of experimental modeling can also be used for the comparison with natural products to explain the formation of natural high-pressure carbon composites after non-graphite precursor. Figures 7. Tables 1. References 64.

Femtosecond Ti: Sa ultra short-pulse laser irradiation effects on the properties and morphology of the zirconia surface after ageing

Femtosecond pulses from a Ti:Sapphire laser were used to irradiate specimens of yttria-stabilised (35% mol) tetragonal zirconia (Y-TZP) with the purpose of studying the effects of the irradiations on their surface properties and morphology after ageing. Zirconia disks were divided into eight groups (n = 32) according to their surface treatment and subsequent ageing: Control: no treatment; sandblasting: Al2O3 sandblasting 50 μm; and ultrashort laser pulses irradiation with 25 μJ pulses, considering two different scanning steps based on the width between two grooves. These groups were duplicated and submitted to ageing. The surfaces were analysed using scanning electron microscopy (SEM), and X-ray diffraction. A finite element analysis, a biaxial flexure test, as well as fractographic and Weibull analyses, were performed. The strengths of the disks were statistically different for the treatment factor, and the principal stresses seemed to be concentrated at the centre of the specimens, as predicted by the computer simulations. Ageing decreased the strengths for all groups and increased the Weibull modulus for the laser group with the 40 μm-width between two grooves. The sandblasting group presented the highest monoclinic phase peak. Although the most significant strength was found within the sandblasting group, the phase transformation was favourable to the laser groups. The Weibull modulus was higher for the laser group with the 60 μm-width between two grooves, confirming the highest homogeneity of its failure distribution. Regardless of the surface treatment, strength was decreased with ageing in all groups. The femtosecond Ti:Sa ultra-short pulse laser irradiation can be suggested as an alternative to the gold standard sandblasting in long-term Y-TZP zirconia rehabilitations, such as crowns and veneers.

Recent Advances in Laser-Induced Surface Damage of KH2PO4 Crystal

As a hard and brittle material, KDP crystal is easily damaged by the irradiation of laser in a laser-driven inertial confinement fusion device due to various factors, which will also affect the quality of subsequent incident laser. Thus, the mechanism of laser-induced damage is essentially helpful for increasing the laser-induced damage threshold and the value of optical crystal elements. The intrinsic damage mechanism of crystal materials under laser irradiation of different pulse duration is reviewed in detail. The process from the initiation to finalization of laser-induced damage has been divided into three stages (i.e., energy deposition, damage initiation, and damage forming) to ensure the understanding of laser-induced damage mechanism. It is clear that defects have a great impact on damage under short-pulse laser irradiation. The burst damage accounts for the majority of whole damage morphology, while the melting pit are more likely to appear under high-fluence laser. The three stages of damage are complementary and the multi-physics coupling technology needs to be fully applied to ensure the intuitive prediction of damage thresholds for various initial forms of KDP crystals. The improved laser-induced damage threshold prediction can provide support for improving the resistance of materials to various types of laser-induced damage.

Mechanism of Laser Immersion-Processing of Glass

The mechanism of the interaction of short-pulse laser radiation with glass and an immersion liquid in which a workpiece is immersed was investigated.