Effect Of Laser Pulse Width Research Articles

Effect of nanosecond laser pulse width and energy on damage characteristics in carbon fibre reinforced plastic (CFRP) laminates

AbstractThis study explores the effects of laser pulse width and energy on CFRP laminates damage in laser bond inspection technology. Three testing programs were used, including varying laser energy while keeping pulse width constant, altering pulse width while maintaining constant power density, and modifying pulse width while keeping energy constant. The results show that when the pulse width remains constant, increased laser energy has a minimal effect on the initial damage location but leads to gradual interlayer delamination and fiber fracture propagation toward the impact surface. With constant laser energy, a specific threshold for pulse width is observed. When the laser pulse width is below this threshold, it exhibits a positive correlation with the damage characteristics of CFRP laminates, whereas when it exceeds this threshold, it shows a negative correlation. Power density correlates with damage when pulse width is constant, but there is no direct correlation when pulse width varies.Highlights CFRP laminates underwent laser shock tests with varying pulse widths. Power density is positively correlated with damage under specific conditions. There exists a specific threshold for laser pulse width. In single‐sided laser shock, initial damage spreads within a specified range.

Laser Powder Bed Fusion of 316L Stainless Steel: Effect of Laser Polishing on the Surface Morphology and Corrosion Behavior

Recently, laser polishing, as an effective post-treatment technology for metal parts fabricated by laser powder bed fusion (LPBF), has received much attention. In this paper, LPBF-ed 316L stainless steel samples were polished by three different types of lasers. The effect of laser pulse width on surface morphology and corrosion resistance was investigated. The experimental results show that, compared to the nanosecond (NS) and femtosecond (FS) lasers, the surface material’s sufficient remelting realized by the continuous wave (CW) laser results in a significant improvement in roughness. The surface hardness is increased and the corrosion resistance is the best. The microcracks on the NS laser-polished surface lead to a decrease in the microhardness and corrosion resistance. The FS laser does not significantly improve surface roughness. The ultrafast laser-induced micro-nanostructures increase the contact area of the electrochemical reaction, resulting in a decrease in corrosion resistance.

Effect of Laser Pulse Width and Intensity Distribution on the Crystallographic Characteristics of GeSn Film

Germanium-tin (GeSn) alloy is considered a promising candidate for a Si-based short-wavelength infrared range (SWIR) detector and laser source due to its excellent carrier mobility and bandgap tunability. Pulsed laser annealing (PLA) is one of the preeminent methods for preparing GeSn crystal films with high Sn content. However, current reports have not systematically investigated the effect of different pulse-width lasers on the crystalline quality of GeSn films. In addition, the intensity of the spot follows the gaussian distribution. As a result, various regions would have different crystalline properties. Therefore, in this study, we first provide the Raman spectra of several feature regions in the ablation state for single spot processing with various pulse-width lasers (continuous-wave, nanosecond, femtosecond). Furthermore, the impact of laser pulse width on the crystallization characteristics of GeSn film is explored for different single-spot processing states, particularly the Sn content incorporated into GeSn crystals. The transient heating time of the film surface and the faster non-equilibrium transition of the surface temperature inhibit the segregation of the Sn component. By comparing the Raman spectra of the pulsed laser, the continuous-wave laser shows the most acute Sn segregation phenomenon, with the lowest Sn content of approximately 2%. However, the femtosecond laser both ensures crystallization of the film and effective suppression of Sn expulsion from the lattices, and the content of Sn is 8.07%, which is similar to the origin of GeSn film.

Magnesium nanoparticle synthesis from powders via LASIS – Effects of liquid medium, laser pulse width and ageing on nanoparticle size, concentration, stability and electrical properties

Mg nanoparticles (NPs) in a range of sizes (20–213 nm) were fabricated via LASIS from powders within two different liquid mediums, namely DI water and isopropyl alcohol for the first time. The effect of laser pulse width (0.60, 0.92 and 1.24 ns) and liquid medium on the UV–Visible and Fourier-transform infra-red spectra, zeta potentials, concentration (particles/ml), colloidal density, mean NP size and electrical properties were investigated. Nanoparticle ageing experiments were conducted whereby the NP size was analysed soon after fabrication and then again after 9-months of shelf life at room temperature. The effect of the colloid storage temperature after fabrication (−17, 4 and 20 °C) on the NP concentration was investigated. DI water-synthesised Mg NPs tend to be larger (89 ± 4 nm) than IPA-synthesised Mg NPs (52 ± 6 nm). IPA-synthesised NPs provided better colloidal stability (zeta potential = +158.7 ± 13.5 mV) than DI water (zeta potential = +16.6 ± 3.1 mV). Mg NPs reduced the resistivity of glass from 102 to 92 Ω/square which gave them a potential application in electronics. Mg NPs have versatile applications including surface coating, printed electronics, battery technology and antibacterial agents.

Effect of fs/ps laser pulsewidth on ablation of metals and silicon in air and liquids, and on their nanoparticle yields

The effect of laser pulsewidth, tuned in the range τ = 0.3–10 ps, on infrared (IR) laser ablation (LA) thresholds of bulk gold, silver and silicon in air and in liquid environments (deionized water, isopropyl alcohol (IPA)) was studied in this work. The influence of laser pulsewidth on the morphology and yield of the ejected nanoparticles (NPs), as well as its impact on the efficiency of NP generation, was studied by UV–vis spectral measurement of the extinction coefficient spectra of NP colloids, fabricated by multi-pass ablation of bulk targets in both solvents at different pulse duration values, by analytical disc centrifuge and by high-resolution scanning electron microscopy. The ablation thresholds are raising with the increase of laser pulsewidth, exhibiting sublinear dependences. The extinction coefficient dependence on τ exhibited a non-monotonous character in case of water medium for all materials, and was gradually descending in case of LA in IPA. Additional MD-TTM (molecular dynamics- two-temperature model) modeling was performed for single-shot laser exposition of bulk Au target in air with τ = 0.3 ps and 4 ps, which allowed distinguishing the main mechanisms of the material removal, the formation of NPs, and the observed crater topography. The performed simulations supported the trend on the ablation threshold increase with the increase of laser pulse duration.

Selective Laser Sintering of Laser Printed Ag Nanoparticle Micropatterns at High Repetition Rates.

The increasing development of flexible and printed electronics has fueled substantial advancements in selective laser sintering, which has been attracting interest over the past decade. Laser sintering of metal nanoparticle dispersions in particular (from low viscous inks to high viscous pastes) offers significant advantages with respect to more conventional thermal sintering or curing techniques. Apart from the obvious lateral selectivity, the use of short-pulsed and high repetition rate lasers minimizes the heat affected zone and offers unparalleled control over a digital process, enabling the processing of stacked and pre-structured layers on very sensitive polymeric substrates. In this work, the authors have conducted a systematic investigation of the laser sintering of micro-patterns comprising Ag nanoparticle high viscous inks: The effect of laser pulse width within the range of 20–200 nanoseconds (ns), a regime which many commercially available, high repetition rate lasers operate in, has been thoroughly investigated experimentally in order to define the optimal processing parameters for the fabrication of highly conductive Ag patterns on polymeric substrates. The in-depth temperature profiles resulting from the effect of laser pulses of varying pulse widths have been calculated using a numerical model relying on the finite element method, which has been fed with physical parameters extracted from optical and structural characterization. Electrical characterization of the resulting sintered micro-patterns has been benchmarked against the calculated temperature profiles, so that the resistivity can be associated with the maximal temperature value. This quantitative correlation offers the possibility to predict the optimal process window in future laser sintering experiments. The reported computational and experimental findings will foster the wider adoption of laser micro-sintering technology for laboratory and industrial use.

Formation mechanism of hierarchical Micro- and nanostructures on copper induced by low-cost nanosecond lasers

Hierarchical surface micro- and nanostructures have attracted much attention in recent years due to their important roles in many applications. Among numerous techniques, ultrafast laser surface texturing technology has gained great success in recent years due to its flexibility and controllability in preparing large-area hierarchical micro- and nanostructures on a wide range of metal surfaces. However, recent studies have demonstrated that low-cost nanosecond (ns) lasers are also reliable tools to induce hierarchical micro- and nanostructures formation on metals, but the underlying formation mechanism is not yet understood. In this study, by observing the morphology evolution of surface structures, we proposed that the formation of surface hierarchical micro- and nanostructures originates from the accumulation of laser-induced resolidified materials and the redeposition of laser-induced plume. On one hand, our proposed mechanism explains the effect of laser pulse width on the morphology of surface structures, and, on the other hand, it explains some phenomena observed in other studies, which can benefit potential applications of this technology in different areas.

Closed-form solutions for thermal stress in solid material induced by long pulsed laser with influence of atmospheric thermal blooming

In this paper, thermal stress of material irradiated by a distorted long pulsed laser considering the influence of atmospheric thermal blooming is modeled. By using analytical expression of laser intensity with atmospheric thermal blooming, axisymmetric heat transfer and thermal elasticity model of distorted long pulsed laser irradiating material is established. Integral transform method is used to solve the governing equation and closed-form solutions of thermal stress are obtained. We studied the effects of laser pulse width, laser propagation distance and intensity of undistorted laser beam on the thermal stress distributions of the material. Modeling results show that, the pulse width, the laser propagation distance in the atmosphere and the undistorted laser intensity have a significant effect on the thermal blooming, and then affects the thermal stress distribution of the material. The greater the pulse width of the laser, the larger the maximum value of the compressive stress. The smaller the propagation distance of the laser in the atmosphere, the larger the maximum value of the compressive stress. And the greater the laser peak power density, the larger the maximum value of the compressive stress.

Effect of laser pulse width on wave packet motion in femotosecond pump-probe pulses

The dependence of the wave packet process of three-level ladder K2 molecules on pulse width was investigated via time-dependent wave packet method, and was firstly quantified. There is no Autler-Townes splitting in the photoelectron spectrum with weaker pump intensity or shorter pulse width. The oscillation period of wave packet increases and the oscillation amplitude decreases with increasing pulse width. The pulse width affects Rabi oscillation, which results in the periodical change of the populations of the electronic state. Quantifying its effect on the population of the excited state shows that the change frequency varies with increasing pump intensity. The results illustrates that the needed population in electronic state of interested can be obtained by controlling pulse width, which provide some important basis for light manipulation of molecular processes experimentally.

Nonlinear transmittance and optical power limiting in magnesium ferrite nanoparticles: effects of laser pulsewidth and particle size

We report comparative measurements of size dependent nonlinear transmission and optical power limiting in nanocrystalline magnesium ferrite (MgFe2O4) particles excited by short (nanosecond) and ultrashort (femtosecond) laser pulses.

Effect of the laser pulse width on the field evaporation behavior of metals and oxides

The laser assisted field-evaporation of metals and oxides strongly depends on the illumination conditions. Here we study the effect of laser pulse width using two different laser systems, with a pulse duration of a few tens of femtoseconds and a few tens of picoseconds, respectively. Adjusting the laser wavelength by nonlinear optical conversion systems, we study the evaporation behavior of FeCu and MgO samples. We prove that the laser pulse width does not affect the evaporation behavior, in the range of duration explored. These results are explained taking into account the absorption behavior of nanometric samples and their thermal properties.

Study on the photodetachment wave packet dynamics of H- ion in a gradient electric field

Using the combination of the time-dependent perturbation theory and the closed-orbit theory, we put forward a calculation formula for the autocorrelation function of H ion in a gradient electric field, and then calculate and analyze the autocorrelation function of the system. Especially, we discuss the effect of laser pulse width, electric field strength and the electric field gradient on the autocorrelation function of H ion in a gradient electric field. It is demonstrated that when the laser pulse width is very narrow, far less than the period of the detached electron, the quantum wave packet revival phenomenon is significant. A series of sharp reviving peaks appear in the autocorrelation function, which are caused by the interference between the returning electron wave packets travelling along the closed orbit and the outgoing electron wave packets. However, with the increase of laser pulse width, the quantum wave packet revival phenomenon becomes weakened. When the difference between the pulse width and the period of the closed orbit is not very large, the reviving peaks in the autocorrelation function become widely spread gradually and the oscillatory structures get flattened. This correspondence will vanish finally due to the interference between the adjacent peaks. In addition, our study also suggests that the background electric field strength and the electric field gradient in the gradient electric field can also have significant effects on the autocorrelation function. With the increase of background electric field strength and electric field gradient, the period of the detached electron's closed orbit gets shorter, the number of the revival peaks in the autocorrelation function is increased gradually, and the quantum wave packet revival phenomenon will be enhanced. Therefore, we can control the autocorrelation function of the hydrogen negative ion by changing the laser pulse width and the external electric field strength. Our results will provide some reference values for the experimental research on the wave packet dynamic property of atoms or ions in external fields.

Effect of Laser Pulse Width on the Laser Lift-off Process of GaN Films

Laser lift-off (LLO), by which GaN is separated from sapphire, is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices. Its physical insight, however, is still not fully understood. We study systematically the effect of laser pulse width on the LLO process and the property of GaN. To estimate accurately the temperature distribution and the decomposed thickness of GaN, fluctuation in the pulse laser energy is taken into account. It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width. In addition, less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area, lower transient temperature and lower N2 vapor pressure encountered during LLO. Some experimental results reported in literature are explained well. Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures.

Laser synthesis and size tailor of carbon quantum dots

Carbon quantum dots (C-dots) with average sizes of about 3, 8, and 13 nm were synthesized by laser irradiation of graphite flakes in polymer solution. The obtained C-dots display size and excitation wavelength dependent photoluminescence behavior. The size control of C-dots can be realized by tuning laser pulse width. The original reason could be the effects of laser pulse width on the conditions of nucleation and growth of C-dots. Compared with short-pulse-width laser, the long-pulse-width laser would be better fitted to the size and morphology control of nanostructures in the different material systems.

Effect of laser parameters on plasma shielding in single and double pulse configurations during the ablation of an aluminium target

The process of nanosecond-laser ablation in air is a complex phenomenon, where the drilling process is a plasma mediated mechanism strongly affected by the shielding of the trailing part of the laser pulse. The laser pulse parameters as well as the target and ambient gas properties affect the dynamics of the process, modifying the importance and the initiation times of plasma shielding and laser-supported wave mechanisms. In this paper, the laser–target coupling of a Nd : YAG laser pulse in air at 1.06 µm impinging on an aluminium target was investigated by spectroscopic analysis of plasma emission and by inspection of craters with video-confocal microscopy. The effects of laser pulse width and energy were investigated both in the single pulse configuration and in the orthogonal pre-pulse double pulse configuration. While in the single pulse case, a strong plasma shielding is observed at irradiances higher than (7–9) × 108 W cm−2, which is thought to coincide with the onset of laser-supported wave mechanism, such a change of regime is not observed in the double pulse case. A physical interpretation of the data is proposed.

Nanosecond pulse width dependence of nonphotochemical laser-induced nucleation of potassium chloride

The effect of laser pulse width on the efficiency of nonphotochemical laser-induced nucleation (NPLIN) of supersaturated aqueous solutions of KCl has been studied. At equivalent peak-power densities it was observed that the same fractions of samples were nucleated for both short (6 ns) and long (200 ns) near-infrared laser pulses. The results show that the efficiency depends on the peak-power density and not on the duration, or total energy, of the laser pulses. It is concluded that the mechanism is unlikely to be based solely on diffusion of solute to a sub-critical cluster.

Tin laser-produced plasma source modeling at 13.5nm for extreme ultraviolet lithography

Extreme ultraviolet lithography semiconductor manufacturing requires a 13.5nm light source. Laser-produced plasma emission from Sn V–Sn XIV ions is one proposed industry solution. The effect of laser pulse width and spatial profile on conversion efficiency is analyzed over a range of power densities using a two-dimensional radiative magnetohydrodynamic code and compared to experiment using a 1.064μm, neodymium:yttrium aluminium garnet laser on a planar tin target. The calculated and experimental conversion efficiencies and the effects of self-absorption in the plasma edge are compared. Best agreement between theory and experiment is found for an 8.0ns Gaussian pulse.

Effect of laser pulse width on material phenomena in ultrathin metal films irradiated by an ultrafast laser: molecular-dynamics study

Using molecular-dynamics computer simulation, we study the material processes occurring for fixed laser fluence in a thin metal film induced by ultrafast laser irradiation. The simulation algorithm combines molecular-dynamics for the atom motion supplemented by an analytical solution of time dependence of the homogeneous electron dynamics. Our results show that the laser pulse duration influences virtually all material processes in the irradiated film: melting, build-up of compressive and tensile pressure, spallation and cluster formation. In particular, for the same laser fluence, a reduction of the laser pulse duration leads to more pronounced pressure peaks in the film, which may induce thermomechanical spallation of the sample, and—at higher fluences, where the ablated material forms a vapour cloud—to an increase in the number of large droplets in the vapour cloud. If the laser pulse duration is smaller than the electron–phonon relaxation time in the material, the latter quantity becomes dominant in limiting the material processes.

Melting and resolidification of gold film irradiated by nano- to femtosecond lasers

Rapid melting and resolidification of a free-standing gold film subject to nano- to femtosecond laser pulses are investigated using the two-temperature model in conjunction with an interfacial tracking method. The interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, in the ultra-fast phase-change process are obtained by considering the interfacial energy balance and nucleation dynamics. A nonlinear electron heat capacity and a temperature-dependent electron–lattice coupling factor for the rapid phase change are taken into account. Effects of laser pulse width and fluence on melting and resolidification are also studied.

흡광 액체의 펄스 레이저 가열에 의해 생성된 기포 거동의 실험적 해석

The bubble dynamics induced by direct laser heating is experimentally analyzed as a first step to assess the technical feasibility of laser-based ink-jet technology. To understand the interaction between laser light and ink, the absorption spectrum is measured for various ink colors and concentrations. The hydrodynamics of laser-generated bubbles is examined by the laser-flash photography. When an Ar ion laser pulse (wavelength 488 ㎚) with an output power up to 600 mW is incident on the ink solution through a transparent window, a hemispherical bubble with a diameter up to ~100 ㎛ can be formed with a lifetime in a few tens of microsecond depending on the laser power and the focal-spot size. Parametric study has been performed to reveal the effect of laser pulse width, output power, ink concentration, and color on the bubble dynamics. The results show that the bubble generated by a laser pulse is largely similar to that produced by a thin-film heater. Consequently, the present work demonstrates the feasibility of developing a laser-actuated droplet generation mechanism for applications in ink-jet print heads. Furthermore, the results of this work indicate that the droplet generation frequency is likely to be further increased by optimizing the process parameters.