Ultrashort Pulsed Laser Ablation Research Articles

Influence of working parameters on multi-shot femtosecond laser surface ablation of lithium niobate

This paper presents an experimental investigation on the ultrashort pulsed laser ablation of 128° Y-cut Lithium Niobate (LiNbO3) using multi-shot fs-laser pulses at different pulse repetition frequencies (1, 10 and 100kHz). The ablation threshold fluence was observed to rapidly decrease as the number N of incident laser pulses increased, regardless of the repetition frequency. This behavior, compatible with the incubation effect, was accurately modeled by a power law. The calculated single pulse ablation threshold Fth,1=1.98±0.15J/cm2 is consistent with values reported in existing literature. The incubation coefficient S∗ appears to be independent of the repetition frequencies. In contrast, the asymptotic ablation threshold Fth,∞ decreased as the repetition frequency was increased. The study delves deeper into the impact of laser operational variables, including pulse energy, repetition frequency, total pulse count, and scanning speed, on the surface roughness and milled depth of fs-laser micromilled zones on LiNbO3 substrates. A discernible trade-off between achieving control over the obtained depth and the surface finish of the process was identified, providing valuable insights for achieving precise control over fs-laser processing of LiNbO3 surfaces.

Mechanical Abrasion of Laser‐Machined Highly Hydrophobic Stainless Steel Surface Depending on Surface Topography

Stainless steel (SST) is an important material for a variety of applications including construction, food, and medical. Highly hydrophobic wetting properties enhance the surface properties of SST to support processes such as self‐cleaning . However, applications also require long‐term stability of such properties against chemical and mechanical influences from the environment or technical processes. Therefore, the reduction of highly hydrophobicity of chemically modified, laser‐textured SST surfaces is investigated in relation to abrasive wear using hierarchical structures, micro‐/nanotextured surface, and support structures that shield the highly hydrophobic pattern. Surface textures comprising ridges, grooves (size: 50–500 μm; depth: up to 100 μm), and a nanostructured grooves bottom are machined by infrared ultrashort pulse laser ablation into SST and are subsequently chemically modified by a self‐assembled monolayer of a fluorinated, phosphonic acid‐modified alkane. Abrasive wear tests of these surfaces show decreasing water contact angles with increasing wear of the modified surface of the support structures. However, there is good stability of the highly hydrophobic properties due to the protection of modified areas at the groove bottom. The proposed wetting model for such designed functionalized laser textures shows possibilities for further optimization of such robust highly hydrophobic surfaces and adaptation to specific applications.

UV-ultrashort pulsed laser ablation of fused silica

The authors report on ultraviolet ultrashort pulsed laser ablation of fused silica and compare the achievable micromachining results to those obtained by using the fundamental emission wavelength in infrared. Ablation in ultraviolet reveals a stable efficiency for increasing fluences, whereas using an infrared beam exhibits a decreasing trend of the ablation efficiency at higher and increasing fluences. In addition, a significant improvement in the surface quality is found by using an ultraviolet wavelength in a fluence range up to 20 J/cm2 compared to infrared, e.g., revealing an Ra of down to 0.45 μm on using the ultraviolet wavelength compared to Ra = 0.56 μm on using infrared at fluences up 15 J/cm2. Moreover, taking advantage of the high available pulse energy, the authors compare the achievable ablation efficiency and surface roughness using a conventionally focused ultraviolet beam and a defocused ultraviolet beam, finding that the defocused ultraviolet beam possesses a processing quality comparable to that of the focused beam. Finally, the authors exemplify the potential of ultraviolet ultrashort pulsed laser ablation by using a Tesla mixer for microfluidic integration of fused silica.

Analysis of processing efficiency, surface, and bulk chemistry, and nanomechanical properties of the Monel® alloy 400 after ultrashort pulsed laser ablation

Monel® alloy 400 has excellent corrosion resistance and finds applications in marine industries. The processing of marine components requires high processing efficiency and a quality finish. Hence, this research aims to investigate the effects of the laser processing parameters such as laser fluence, scanning velocity, hatching distance, and the scanning pass on the ablation rates and efficiency, chemistry, and nanomechanical properties of the Monel® alloy 400 after pulsed picosecond (ps) laser ablation. From the experimental findings, the ablation depth increases as the laser fluence increases while decreasing as the scanning velocity increases. Surface roughness was noted to increase as the laser fluence increased. The findings demonstrated that the ablation rate increases as laser fluence increases while ablation efficiency decreases. Energy dispersive x-ray spectroscopy (EDX) showed that the elemental composition of laser-ablated zones is almost similar to that of the polished sample. X-ray spectroscopy (XPS) shows that the outer layer on the surface of Monel® alloy 400 is composed of NiO and CuO. The hardness and Young’s modulus of the laser-processed alloy were found to be less than those of the bulk material. This study can be used to establish optimal processing parameters for the ultrafast ps laser processing of materials to achieve high ablation efficiency with a high-quality surface finish for industrial applications.

Ultra-short pulse laser ablation of metals: A comprehensive 3D simulation perspective enlightening novel process insights

Intricate dynamics in ultra-short pulse laser ablation of metals necessitate deeper process understanding. This work presents an auspicious contribution in this direction, incorporating a sophisticated three-dimensional finite-volume simulation tool, building upon our previously validated models in continuous-wave laser material processing. Atop the existing multiphysics framework, a two-temperature and a Drude absorption model has been integrated. Focused on laser ablation of copper, preliminary results unveil novel perspectives on the dynamic interaction between thermal effects and material response. Surpassing limitations inherent in one- and two-dimensional descriptions, this model distinctively captures the complex interplay of electron heating, energy transfer to the lattice, and ensuing rapid phase transitions. Crucially, it complements existing insights into ablation mechanism by illustrating the influence of elusive temperature-dependent material properties, such as density and the bulk modulus for superheated liquid metal, on the process. While still in development, these advancements mark a promising stride towards a deeper process comprehension.

The ultrashort pulse laser ablation model of silicon based on the generalized thermoelastic theory with spatio-temporal nonlocal effect

The present work is devoted to establishing the ultrashort pulse laser ablation generalized thermoelastic model with spatio-temporal nonlocal effect and investigating the transient responses of the process of silicon ablated by the picosecond pulse laser. The research is divided into three cases. 1) The solid silicon before the target surface melting is studied, and the transient responses of the final state of this case are taken as the initial conditions of the Case Two. 2) The liquid silicon after the target surface melting is researched, and the heat flux taken away by vaporization is considered in the boundary condition. 3) The solid silicon after the target surface melting is discussed, and the moving solid-liquid interface is regarded as the coordinate origin. The coupled governing equations containing spatial nonlocal parameter, time delay factor, and kernel function are established and solved by the Laplace transform together with its numerical inversion. The melting time and depth of target are emphatically discussed. The temperature, displacement and stress with different laser intensity, spatial nonlocal parameter, time delay factor, kernel function as well as time are obtained and illustrated graphically.

Scaling up picosecond laser ablation of a LATGP-type glass-ceramic solid electrolyte for all-solid-state battery production

All-solid-state batteries are an intensively studied technology expected to complement conventional lithium-ion batteries in the near future. Research into fundamental production processes is crucial for enabling economic, industrial-scale all-solid-state battery production. Laser radiation is a production tool suited for contour cutting and surface structuring of inorganic solid electrolyte separators. In the scope of this work, the laser ablation of the commercial glass-ceramic solid electrolyte lithium aluminum germanium titanium phosphate (LAGTP) using ultrashort-pulsed laser radiation at different wavelengths, fluences, and pulse repetition rates is studied. Ablation thresholds, efficiencies, and rates were determined by manufacturing percussion drillings, trenches, and cavities. Geometry dependencies, such as the ablation rate decay with advancing depth during laser cutting, necessitated an application-oriented determination of ablation metrics. The surface qualities of the solid electrolyte layers were evaluated after laser ablation by scanning electron microscopy and surface roughness measurements. A wavelength of 532 nm was found to be beneficial compared to shorter and longer wavelengths in terms of productivity and ablation quality, reaching volume ablation efficiencies up to 36 μm3∙μJ−1 and surface roughnesses Sa below 500 nm. The determined metrics are discussed for ablation cutting and structuring of solid electrolyte layers in all-solid-state battery production, considering throughput and surface quality. The results provide insight into the ablation behavior of glass-ceramic materials and support the application of ultrashort-pulsed laser ablation in next-generation battery production.

Ultra-short pulsed laser ablation of decagonal AlCoNi and AlCoCuNi quasicrystals

Al70Co20Ni10 and Al70Co15Cu10Ni5 (at%) decagonal quasicrystals (DQCs) were subjected to femtosecond laser ablation at a laser wavelength of 800 nm, in deionized water (DI). The generated nanoparticles (NPs) confined within the liquid medium were studied for optical and structural properties. The structural analysis revealed the retention of the targets phase in the NPs. In case of Al70Co20Ni10, formation of Al3Ni2 phase was confirmed through the SAED patterns and HRTEM micrographs. Contrary to this, the formation of Al-Ni phase was not observed in Al70Co15Cu10Ni5. This is attributed to the presence of Cu in the latter sample, which restricts the mixing of Ni with Al. The HRTEM micrographs in both cases showed that Al2O3 was present at the edges of the NPs. The optical analysis confirmed the formation of Al2O3 in both cases. However, in the case of Al70Co15Cu10Ni5, a very weak signal corresponding to CuO was detected. This is attributed to the diffusion of Cu along with Al at the edge. The ablated region of the target’s surface was studied for the formation of laser-induced periodic surface structures (LIPSS) also known as ripples, and the type of ripples formed was identified.

Resolving transient temperature and density during ultrafast laser ablation of aluminum

To understand the dynamics of ultrashort-pulse laser ablation, the interpretation of ultrafast time-resolved optical experiments is of utmost importance. To this end, spatiotemporally resolved pump-probe ellipsometry may be utilized to examine the transiently changing dielectric function of a material, particularly when compared to two-temperature model simulations. In this work, we introduce a consistent description of electronic transport as well dielectric function for bulk aluminum, which enables unambiguous quantitative predictions of transient temperature and density variations close to the surface after laser excitation. Potential contributions of these temperature and density fluctuations to the proposed optical model are investigated. We infer that after the thermal equilibrium of electrons and lattice within a few picoseconds, the real part of the dielectric function mostly follows a density decrease, accompanied by an early mechanical motion due to stress confinement. In contrast, the imaginary part is susceptible to a complicated interaction between time-varying collision frequency, plasma frequency, and a density dependency of the interband transitions. The models proposed in this study permit an outstanding quantitative prediction of the ultrashort-pulse laser ablation’s final state and transient observables. Consequently, it is anticipated that in the future, these models will provide a quantitative understanding of the dynamics and behavior of laser ablation.Graphical abstract

Ultra-short Pulse Laser Ablation for Cross-section of Auto Body Paints.

Ultra-short Pulse Laser Ablation for Cross-section of Auto Body Paints.

How Pulse Width Affects Laser Ablation of Organic Liquids.

Laser synthesis in liquids is often carried out in organic solvents to prevent oxidation of metals during nanoparticle generation and to produce tailored carbon-based nanomaterials. This work investigates laser ablation of neat organic liquids acetone, ethanol, n-hexane, and toluene with pulse widths ranging from 30 fs to 4 ps through measurements of reaction kinetics and characterization of the ablation products with optical spectroscopy and mass spectrometry. Increasing the pulse width from 30 fs to 4 ps impacts both the reaction kinetics and product distributions, suppressing the formation of solvent molecule dimers and oxidized molecules while enhancing the yields of gaseous molecules, sp-hybridized carbons, and fluorescent carbon dots. The observed trends are explained in the context of established ionization mechanisms and cavitation bubble dynamical processes that occur during ultrashort pulsed laser ablation of liquid media. The results of this work have important implications both for controlling the formation of carbon shells around metal nanoparticles during the ablation of solid targets in liquid and producing carbon nanomaterials directly from the ablation of organic liquids without a solid target.

Microscopic mechanism of ultrashort-pulse laser ablation of metals: a molecular dynamics study incorporating electronic entropy effects

The microscopic mechanism of metal ablation induced by ultrashort laser pulse irradiation is investigated. A two-temperature model scheme combined with molecular dynamics (TTM-MD) is developed to incorporate electronic entropy effects into the simulation of metal ablation while satisfying the energy conservation law. Simulation with the TTM-MD scheme reveals that ultrashort laser pulse irradiation near the ablation threshold causes high-energy atom/ion emission and sub-nanometer depth ablation, as observed experimentally, due to the electronic entropy effect. It is also shown that the electronic entropy effect is also significant in spallation.

Relative control of domains’ structure in Grain-Oriented electrical steels by Ultra-Short Pulsed laser ablation process

This paper investigates the impact of surface Ultra-Short-Pulsed-Laser ablation process (USPL), mainly the groove depth, shockwave pressure and pattern, on magnetic characteristics of Grain-Oriented Electrical Steels (GOES) by using the Tensor Magnetic Phase Theory (TMPT). A sensitivity analysis to key laser parameters helps specifying the process thanks to a relative control of the surface magnetic structure (Magneto-Optical Indicator Film (MOIF)), dynamics and the behaviors (Single Sheet Tester (SST)) that follow.

Numerical simulation and investigation of ultra-short pulse laser ablation on Ti6Al4V and stainless steel

In ultra-short pulse laser machining and micro/surface processing, accurate simulation of laser ablation is important for understanding laser-target interaction and improving ablation performance, but it remains challenging. This work aims to develop a numerical model to improve the accuracy of the ablation depth calculation. A grid deformation scheme is proposed based on energy conservation and considering contributions to instant material removal from both the electron and lattice subsystems. By incorporating this scheme with the two-temperature model (TTM), a reasonable prediction of the instant target surface profile during laser ablation has been achieved. In the case of single-pulse femtosecond laser ablation of Ti6Al4V, the calculated ablation depth ranges from 0.06 to 0.56 μm for laser energy from 1.0 to 10.0 μJ. For single-pulse picosecond laser ablation of stainless steel, as laser energy increases from 6.0 to 18.5 μJ, the predicted ablation crater deepens accordingly from 40 to 87 nm. In addition, for multi-pulse picosecond laser ablation of stainless steel, a linear dependence of the ablation depth on the pulse number is observed up to a depth of about 803 nm at 6.0 μJ and 20 pulses. In all the above-mentioned cases, the calculation results are in better agreement with experimental measurements than conventional TTM or other material removal schemes, validating the accuracy of the proposed model.

Multi-timescale observation of ultrashort pulse laser ablation of copper

Ultrashort pulse lasers have attracted attention because they can be used to fabricate various types of solid materials, including metals, semiconductors, and insulators. To further improve ultrashort pulse laser processing, it is important to understand the phenomena that occur during processing. Optical-delay pump–probe observation is a powerful tool for investigating the ultrafast dynamics of ablation on a timescale ranging from sub-picoseconds to a few nanoseconds. However, the discrepancy in the timescales between ultrafast phenomena and the final processed shape is too large to understand the decisive process leading to the final processed shape. In this study, we combine optical-delay with electrical-delay pump–probe​ shadowgraphy to capture phenomena over a wide range of timescales ranging from a few nanoseconds to hundreds of nanoseconds to clarify the sequence of processes leading to static processing results. Particularly, we found that a ring-shaped molten structure was formed when the pulse duration was 9 ps or longer and revealed the mechanism of the formation by visualizing shock wave propagation and particle ejection from the ring position. This research is expected to contribute to the further understanding and improvement of ultrashort pulse laser processing.

Femtosecond laser processing of advanced technical materials

Ultra-short pulsed laser ablation may be used for high-precision machining with very low thermal influence on the processed materials. Due to this reason, lasers are increasingly used for processing of advanced materials, such as titanium alloys, nickel-based alloys or steel, every year. In this study, four advanced technical materials were analysed and compared under femtosecond laser irradiation with three different wavelengths. The main laser-material interaction parameters were identified, namely the ablation threshold and removal efficiency parameters. Higher removal rates were found for Ti6Al4V alloy with all three harmonic wavelengths. To increase process productivity, a method of increasing the repetition rate and scanning speed was presented. With the maximum repetition rate, the productivity increased five-fold with a similar removed depth and surface quality. Finally, the suitability of the identified parameters with regard to quality and productivity was demonstrated for fabrication of two complex structures – honeycomb and dot – which has the potential to improve friction properties of advanced materials.

Ultrashort pulsed laser ablation of zirconia toughened alumina: Material removal mechanism and surface characteristics

Zirconia toughened alumina (ZTA) is commonly used in hip joint implants and cutting tools. The difference in material properties of the zirconia and alumina phases makes the composite inhomogeneous at the grain size level. Due to the strong nonlinear laser absorption mechanisms of wide band gap materials under intense laser field, the smaller band gap zirconia phase can absorb a significantly larger amount of laser energy than the alumina phase. The nonuniform energy deposition and lattice heating takes place at a comparable timescale as the laser pulse duration, which is too short for thermal diffusion to play a role. As a result, the temperature in the zirconia phase can be significantly higher than in the alumina phase, leading to a unique selective phase melting phenomenon, i.e. localized melting of the higher melting point zirconia phase (2715 °C) surrounded by a lower melting point alumina phase (2072 °C) which remains solid. This phenomenon makes the material removal mechanism of the nanocomposite significantly different from that of single-phase materials under ultrashort pulsed laser processing. On the basis of experimental analysis and theoretical modelling, material ablation by the disintegration of alumina grains due to the localized melting of the zirconia phase was identified.

Investigation on Subsurface Damage Patterns in Ultrashort Pulse Laser Machining of Glass using Optical Coherence Tomography

Ultrashort pulse (USP) laser ablation is gaining popularity as a novel manufacturing technique for brittle materials, enabling the creation of complex freeform shapes that are challenging to produce with conventional optics manufacturing techniques. Freeforms have revolutionized optics manufacturing by providing designers with increased degrees of freedom using non-rotational symmetric components. However, this evolution presents new challenges for manufacturing processes, calling for innovative solutions such as USP ablation. To ensure the industrial viability of areal USP laser machining, it is crucial to not only consider material removal rates but also surface quality and subsurface damage (SSD). Especially for optical applications, harsh quality requirements must be met. This study investigates the SSD patterns of fused silica (FS) and borosilicate glass N-BK7 (BK) processed under different laser wavelengths, beam geometries and processing parameters using high-resolution optical coherence tomography (OCT). It is shown that OCT as non-destructive and 3D evaluation method is well-suited for analysing USP processes. The discovered differences in defect morphology between FS and BK emphasize the importance of selecting appropriate processes and process parameters when working with different materials. Compared to previous studies, for the parameter sets analysed here using OCT, much higher defects depths of up to 441 µm were revealed.

Strip waveguides in Yb3+-doped silicate glass formed by combination of He+ ion implantation and precise ultrashort pulse laser ablation

Abstract Strip optical waveguides were realized in Yb3+-doped silicate glass with ultrashort pulse laser ablation assisted He+ ion implantation. Planar waveguides were first prepared near the glass surface by He+ ion implantation (450 keV + 500 keV + 550 keV), followed by annealing at 260℃. After that, under the processing parameters of 3 μJ energy and 50 μm/s ablation velocity, two parallel tracks with separation of 15, 20, and 25 μm were, respectively, inscribed on the sample, which confine the light in lateral direction to form a strip waveguide. The near-field intensity measurement indicates that the strip waveguides maintain the single-mode propagation characteristics with 976 nm laser injection, and present the multi-mode characteristics with 632.8 nm laser injection, showing that the guided modes are well supported in the strip waveguides. The minimum propagation loss of strip waveguide is 1.35 dB/cm. Fluorescence emission spectra indicate that the gain properties of waveguide core were maintained well after waveguide preparation, revealing that the strip waveguide device in Yb3+-doped silicate glass has the potential to become an active device as waveguide laser or waveguide amplifier.

Particle Re-Deposition During Ultrashort Pulse Laser Ablation of ITO Thin Films Using Single- and Multi-Beam Processing

Particle Re-Deposition During Ultrashort Pulse Laser Ablation of ITO Thin Films Using Single- and Multi-Beam Processing