Nanosecond Laser Research Articles

The shock wave evolution of the laser-induced breakdown under non-spherical symmetry using a 1064 nm nanosecond laser

In acoustics-related interdisciplinary areas, the shock wave of laser-induced breakdown has garnered significant attention. However, research on the propagation of shock waves in non-spherical symmetry is insufficient in both theoretical and experimental aspects. This paper aims to thoroughly study the evolution of underwater shock wave directivity by employing the method of shadowgraph. The shock wave front is determined by the dark fringes in the shadowgraph image and the normal propagation speed of the shock wave is calculated using Huygens principle. Subsequently, normal propagation speed is converted to pressure in different directions by employing the equation of state of the medium. It has been found that the spherical plasma produces an isotropic shock wave, whereas filamentary plasma generates a highly anisotropic one. To evaluate the anisotropic property of the shock wave, we introduce pressure directivity, which is defined as the pressure at any direction normalized by the maximum value. The temporal evolution of shock wave pressure directivity is obtained based on the shadowgraph images. In the case of filamentary plasma, there is a sudden transition of the pressure directivity in the axial from 40 ns to 165 ns, after which the pressure directivity is consistent with the hydrophone measurement. Based on the moving breakdown model of the plasma and the superposition principle, we propose a theoretical model to explain the experimental result of the pressure directivity. The outcome of our model exhibits considerable consistency with the experiment.

Enhancement of laser ablation via high-frequency electromagnetic induction heating

The efficiency of pulsed laser ablation has always been the focus point of research. A novel high-frequency electromagnetic induction heating-assisted laser ablation scheme is proposed and investigated to enhance the efficiency and improve the surface processing quality during the nanosecond laser ablation of metal substrates. To reduce laser energy required to reach the ablation threshold of metal, this method utilizes the electromagnetic induction to rapidly elevate substrate temperature, making the metal easier to be ablated. The results show that ablation width increases 16% and ablation depth increases 31% with the assistance of electromagnetic induction heating at a laser fluence of 1.32 J/cm2, which increases 90% of the laser-ablated volume. Meanwhile, the surface ablation quality is significantly improved due to the smaller temperature gradient around the ablation region. This new method has great potentials in the laser micromachining at a higher processing efficiency and better laser-processed surface quality.

Third-harmonic optical process in Zn:NiO thin films under the influence of femtosecond and continuous wave laser excitation

Abstract In this study, we focused on the impact of nonlinear optical properties on Zn-doped NiO thin film, which was analyzed using z scan and THG technique. The z-scan technique was performed using a continuous wave laser. The open aperture shows that all films exhibit the reverse saturable absorption and the mechanism responsible for two-photon absorption, excited state absorption, and free carrier absorption. The closed aperture results in the negative nonlinear refraction caused by the thermal effects. The enhancement in the third-order susceptibility from 5.37 ×10-3 to 13.24 ×10-3 esu with Zn doping is due to the presence and increase in the concentration of defect levels in the films. The THG studies were performed using femtosecond and nanosecond lasers and revealed that the enhancement in the signal with the rise in Zn doping concentration was attributed to the enhancement of photoexcitation and relaxation processes within the sample. These results suggest that Zn-doped NiO films have significant potential for applications in the realm of optoelectronic applications.

Peristome‐mimetic Surfaces Fabricated by Nanosecond Laser for Uni‐directional Liquid Spreading

Unidirectional liquid transport, which operates without external energy input, has garnered remarkable interests in the global energy sector. A crucial breakthrough in this field involves understanding how liquids spread on the peristome surface of Nepenthes alata. This study, inspired by the microstructural traits of the Nepenthes peristome, has brought about the development of a biomimetic surface on metal substrates using nanosecond laser processing on inclined bases. This process replicates the natural peristome’s microstructure, which allows for controlled liquid spread on the surface. The research also examines how wettability influences unidirectional liquid spread. Additionally, it involves adjusting the microstructure parameters on the biomimetic surface, which leads to variations in edge curvature and microcavity wedge angles. More importantly, this study comprehensively investigates the relationship between these structural changes and the phenomenon of unidirectional liquid transport. The findings suggest that altering edge curvature and micro‐cavity wedge angles can manage the directional spread of liquids. The optimized surface, with ideal curvature and wedge angles, achieves liquid movement speeds up to 12.03mm/s. This represents a notable improvement, 2.2 and 2.7 times faster than the original structure, respectively. These findings provides valuable insight into the design of energy‐independent unidirectional liquid spreading surfaces on metal substrates.This article is protected by copyright. All rights reserved.

Nanosecond-laser cutting of (TiZrHfNbTa)C high-entropy ceramics

(TiZrHfNbTa)C high-entropy ceramics have wide range of application prospects due to their excellent performance, but their hardness and brittleness make them difficult to process. In this study, novel method based on nanosecond laser was used to cut (TiZrHfNbTa)C high-entropy ceramics. Results show that laser machining is efficient strategy for high-precision machining of (TiZrHfNbTa)C high-entropy ceramics. Slit width obtained via nanosecond-laser cutting is only 26.4% of that obtained via mechanical cutting, and average roughness and maximum height difference of cut surface are 2.078 and 20.497 μm, respectively, which are smaller than those obtained through mechanical cutting (4.296 and 29.706 μm, respectively). Furthermore, removal mechanism under the action of nanosecond laser was investigated, and it was found that cut surface of (TiZrHfNbTa)C high-entropy ceramics formed thin oxide recast layer together with carbide underneath. This study provides important results for precision machining of (TiZrHfNbTa)C high-entropy ceramics.

Nanosecond pulsed laser etching anti-reflective gratings and synchronous laser annealing for performance optimization of Ag/AZO thin films

Nanosecond pulsed laser etching for fabricating anti-reflective gratings and inducing synchronous laser annealing was performed on Ag/AZO films. The optimum grating pitch was determined by performance analyses of laser-etched unidirectional gratings, based on which laser-etched bidirectional gratings were fabricated to further determine the optimum grating tilt angle. The results revealed that with the increase of grating pitch, the grating ridge total-side-area was gradually decreased to cause a gradually weakened anti-reflective effect, but the superimposed heat-affected zones between adjacent grooves became smaller or even disappeared, which brought about different synchronous laser annealing effects. The unidirectional grating-textured film with a medium grating pitch of 200 μm showed the best overall performance under the combined influence from anti-reflective gratings and synchronous laser annealing. For the bidirectional gratings, although increasing the grating tilt angle did not change the grating ridge total-side-area, it would enable the laser energy to be more uniformly distributed on the whole film surface, producing a better synchronous laser annealing effect. The bidirectional grating-textured film with a grating tilt angle of 90° had the best overall performance with the highest FOM value of 2.18 × 10−2 Ω−1 that was ∼3.2 times that of the as-prepared film. The results are instructive for preparing high-performance TCO-based films.

Raman spectroscopy of thermo- and laser-induced transformations of gouache paint layer of copper phthalocyanine blue

Methods to control polymorphic modifications of phthalocyanines using optical (laser) radiation and possible photoinduced transformations of polymorphs are of practical interest in problems of identification and attribution of paintings, laser (micro)sampling, and the development of phthalocyanine structures for technical applications in optics, optoelectronics, and medicine. In this work, we compare the thermal and laser-induced changes of a gouache paint layer based on copper phthalocyanine (CuPc) PB15. The thermally induced color changes of the paint layer are quantified using the CIE Lab D65/10 color space. (Nano)rods formed in the paint layer when the sample is heated to 450°C at normal pressure without humidity control are studied using absorption spectroscopy, Raman microspectroscopy, and scanning electron microscopy. It is shown that the formation of (nano)rods is related to the α→β polymorph transition of CuPc. Low-frequency markers of the CuPc β-polymorph are revealed in the Raman spectra. For the sample containing (nano)rods, the a* color coordinate substantially increases (by about 30 units), whereas the L* and b* coordinates remain almost unchanged. Irradiation with a single nanosecond laser pulse at a wavelength of 532 nm leads to the laser ablation of the paint layer at fluences exceeding a threshold level of about 3 J/cm2. Irradiation at fluences of greater than 0.5 J/cm2, but lower than the ablation threshold leads to color change of the paint layer due to the α→ε transition of CuPc. Similar transformations are observed at the periphery of and inside ablation crater.

RHDLPP: A multigroup radiation hydrodynamics code for laser-produced plasmas

In this paper, we introduce the RHDLPP, a flux-limited multigroup radiation hydrodynamics numerical code designed for simulating laser-produced plasmas in diverse environments. The code bifurcates into two packages: RHDLPP-LTP for low-temperature plasmas generated by moderate-intensity nanosecond lasers, and RHDLPP-HTP for high-temperature, high-density plasmas formed by high-intensity laser pulses. The core radiation hydrodynamic equations are resolved in the Eulerian frame, employing an operator-split method. This method decomposes the solution into two substeps: first, the explicit resolution of the hyperbolic subsystems integrating radiation and fluid dynamics; second, the implicit treatment of the parabolic part comprising stiff radiation diffusion, heat conduction, and energy exchange. Laser propagation and energy deposition are modeled through a hybrid approach, combining geometrical-optics ray-tracing in sub-critical plasma regions with a one-dimensional solution of the Helmholtz wave equation in super-critical areas. The thermodynamic states are ascertained using an equation of state, based on either the real gas approximation or the quotidian equation of state (QEOS). For ionization calculations, the code employs a steady-state collisional-radiation (CR) model using the screened-hydrogenic approximation. Additionally, RHDLPP includes RHDLPP-SpeIma3D, a three-dimensional spectral simulation post-processing module, for generating both temporally-spatially resolved and time-integrated spectra and imaging, facilitating direct comparisons with experimental data. The paper showcases a series of verification tests to establish the code's accuracy and efficiency, followed by application cases, including simulations of laser-produced aluminium (Al) plasmas, pre-pulse-induced target deformation of tin (Sn) microdroplets relevant to extreme ultraviolet lithography light sources, and varied imaging and spectroscopic simulations. These simulations highlight RHDLPP's effectiveness and applicability in fields such as laser-induced breakdown spectroscopy, extreme ultraviolet lithography sources, and high-energy-density physics.

Study on nanosecond laser-induced iron plasma reactive etching of single-crystal CVD diamond

Single-crystal diamond has great potential applications in national defense, military, and aerospace fields. However, the high hardness, chemical inertness, and anisotropy bring great challenges to machine microstructures on the diamond. Here, iron plasma, generated by infrared nanosecond laser ablation of a Fe target, was utilized to etch single-crystal diamond. The EDS, Raman, and XPS analysis revealed the formation of iron carbide within the sputtered layer surrounding the diamond microgrooves, thereby confirming that the iron plasma reacts chemically with the diamond. It was observed that employing a reactive metal, such as iron, for etching diamond microgrooves yields improved morphological characteristics and enhanced etching efficiency compared to the use of a non-reactive metal, such as copper. Moreover, the process of material removal through laser-induced iron plasma etching of diamond was elucidated. Subsequently, a systematic investigation was conducted on the impact of processing parameters on the laser-induced iron plasma etching of diamonds. Various periodic microstructures with regular edges and no chipping and cracks were successfully processed on the diamond using suitable laser parameters. This study furnishes a novel approach for the efficient fabrication of high-quality microstructures on single-crystal diamonds.

Elastic wave suppression through additively manufactured petal lattice metamaterials

Lattice-core sandwich structure metamaterials are lightweight alternatives to monolithic materials that can present better mechanical, thermal, and energy dampening performance. Manufacturing lattice metamaterials to follow curved surfaces can pose a challenge, as the lattices rely on their geometric orientation to the substrate for their mechanical properties. This work rationally designed a lattice structure where the surface is broken up into “petals” connected to the underlying lattice, which localizes the petals’ impact response. This design opens a pathway for implementation of lattice-core sandwich structures onto complex surface geometries. These petal structures were evaluated for their energy absorption efficiency experimentally by utilizing pressure waves generated with nanosecond lasers and computationally via finite element modeling. The lattice structures exhibited a two-orders-of-magnitude decrease in transmitted pressure compared to their constituent steel at equivalent mass. Furthermore, localizing energy absorption into petal structures provided a 44% reduction in peak load compared to a continuous “single-petal” design.

Optical energy band gap investigation of the zinc carbide nanoparticles prepared by nanosecond pulsed laser ablation of zinc metals in hexane liquid medium

Many different applications make use of carbide nanoparticles, which could be prepared via conventional techniques, but all of these techniques tend to be intricate, and several steps must be completed before fabrication can begin. However, in this study, we present, for the first time, a straightforward technique for the production of zinc carbide nanoparticles (ZnC) through the use of nanosecond laser ablation of a zinc target immersed in hexane with the assistance of a purged nitrogen gas. We conducted optical absorption spectroscopy on the produced nanostructured materials. We studied the optical properties using the conventional method of the Tauc relation. We compared these values with various innovative approaches, including the absorption spectrum fitting method (ASF) and its derivative method (DASF). We conducted an investigation into each approach's correction to achieve a satisfactory level of agreement between the values, and documented a comparable pattern. These results help us understand the physicochemical properties of zinc carbide and other nanoparticles or nanocomposites that do not have any chemical residues. They make them a possible candidate to improve luminescence catalytic activity, photonics, and optoelectronic applications.

PROSPECTIVE LITHIUM ALUMINOSILICATE GLASS-CERAMIC MATERIALS FOR PULSE RANGEFINDERS

The relevance of creating multi-functional nanosecond pulsed laser devices with a generation wavelength that lies in the conditionally eye-safe region of the spectrum of 1.5÷1.6 μm has been established. The prospects of using the mode of passive Q-switching when receiving powerful nanosecond laser pulses with a radiation divergence close to the diffraction one have been determined. Materials for shutters that function in the mode of passive Q-switching were analyzed: solid-state nonlinear optical materials based on single crystals of yttrium-aluminum garnet doped with cations of neodymium, chromium, vanadium and other Nd- or Yb-doped crystals in the wavelength range of 0.8–1.2 μm. The promising use of oxide single crystals activated by Co2+ ions in four-coordinated oxygen positions for MgAl2O4, LiGa5O8, LaMgAl11O19 has been confirmed. The feasibility of developing transparent glass-ceramics based on aluminomagnesium and lithium gallium spinel for pulsed ranging was determined, taking into account its commercial availability, the simplicity of the production technology, as well as the homogeneity of the distribution of the activator in the volume. The feasibility of creating a new type of nonlinear optical materials based on nanostructured heat-resistant lithium aluminosilicate glass ceramics with spinel nanocrystals activated by Co2+ ions under low-temperature heat treatment conditions, has been determined. The purpose and tasks of the work are formulated, which consist in justifying the choice of the system and compositions of glasses for obtaining glass-ceramic materials as a passive laser shutter for powerful lasers that operate at a wavelength of 1.54 μm and are characterized by high heat resistance. The choice of the lithium aluminosilicate system R2O – RO – RO2 – P2O5 – R2O3 – SiO2 based on phase-forming SiO2, Al2O3, Li2O, modifying K2O is substantiated; RO – MgO, ZnO, CaO, SrO, BaO components and a complex crystallization catalyst of P2O5, CeO2, TiO2, SnO2, ZrO2 and ZnO. The structural criteria for the glass matrix were formulated. Compositions of model glasses were designed taking into account the calculated parameters fSi > 0.22, Kсr ≥ 3.5, Ktr ≥ 2.1, and the probability of obtaining transparent glass-ceramic materials with a sitallized structure for pulse rangefinders was established on their basis.

Diffraction-based approach for real-time monitoring of nanosecond direct laser interference patterning structure formation on stainless steel

Direct Laser Interference Patterning (DLIP) stands out as a versatile and cost-effective method for functionalizing material surfaces at high throughputs. Monitoring the dynamics of the structure formation can lead to a deeper understanding of the interplay between the main factors governing the process and ultimately to optimize the final texture. Here, the formation of gratings on stainless steel by DLIP with ns-pulses is studied using a diffraction-based approach, which measures the time-resolved reflectivity (TRR) of the sample. Measurements are performed for single pulses across different laser fluences. The melting dynamics are analyzed and compared with numerical results. By correlating the recorded signals with the structure depths, growth rates of 11 nm/ns and 57 nm/ns were estimated for fluences of 1.9 J/cm2 and 5.3 J/cm2, respectively. Furthermore, two growth regimes are identified. In the fast growth phase, the melting time increased from 73 to 380 ns for fluences of 1.9 J/cm2 and 5.9 J/cm2, respectively, showing a good agreement with the performed thermal simulations.

Delivery of nanosecond laser pulses by multi-mode anti-resonant hollow core fiber at 1 µm wavelength

In this paper we explore the application of low-loss multimode anti-resonant hollow-core fiber (MM-AR-HCF) in the delivery of nanosecond laser pulses at 1 µm wavelength. MM-AR-HCF with large core offers a rich content of low-loss higher-order modes which plays a key role in the efficient coupling and transmission of high-power laser of low beam quality. In the experiment, laser pulses of an average pulse energy of 21.8 mJ with 14.6 ns pulse width (corresponding a peak power of 1.49 MW) are transmitted through MM-AR-HCF of 9.8 m length without damage. 85% transmission efficiency is achieved where the incident laser beam suffers a low beam quality with M2x and M2y of 2.18 and 1.99 respectively. Laser-induced damage threshold (LIDT) of MM-AR-HCF was measured to be 22.6 mJ for 85% transmission efficiency, which is 7 times higher than that for a multimode silica optical fiber with a large core of 200 µm.

Fabrication of Nanostructures Consisting of Composite Nanoparticles by Open-Air PLD

We present a two-step physical method for the fabrication of composite nanoparticle-based nanostructures. The proposed method is based on the pulsed laser deposition (PLD) technique performed sequentially in vacuum and in air. As a first step, thin-alloyed films of iron with noble metal were deposited by PLD in vacuum. The films were prepared by ablation of a mosaic target formed by equal iron and gold sectors. As a second step, the as-prepared alloyed films were ablated in air at atmospheric pressure as the laser beam scanned their surface. Two sets of experiments were performed in the second step, namely, by applying nanosecond (ns) and picosecond (ps) laser pulses for ablation. The structure, microstructure, morphology, and optical properties of the samples obtained were studied with respect to the laser ablation regime applied. The implementation of the ablation process in open air resulted in the formation of nanoparticle and/or nanoparticle aggregates in the plasma plume regardless of the ablation regime applied. These nanoparticles and/or nanoaggregates deposited on the substrate formed a complex porous structure. It was found that ablating FeAu films in air by ns pulses resulted in the fabrication of alloyed nanoparticles, while ablation by ps laser pulses results in separation of the metals in the alloy and further oxidation of Fe. In the latter case, the as-deposited structures also contain core–shell type nanoparticles, with the shell consisting of Fe-oxide phase. The obtained structures, regardless of the ablation regime applied, demonstrate a red-shifted plasmon resonance with respect to the plasmon resonance of pure Au nanoparticles.

On the Dendrite‐Suppressing Effect of Laser‐Processed Polylactic Acid‐Derived Carbon Coated Zinc Anode in Aqueous Zinc Ion Batteries

A major bottleneck limiting the commercialization of aqueous zinc ion batteries (AZIBs) is dendrite formation on the zinc anode during the plating/stripping process, which leads to rapid performance and device failure. In this regard, researchers are trying to design more stable anodes toward suppressing dendrite formation. One possible solution to tackle this problem and to extend the cycling life of AZIBs is to modify the zinc anode surface by coating carbonaceous materials, enabling controlled charge flux and uniform ion distribution. This work reports a sustainable and bio‐derived polylactic acid (PLA) as a coating layer on the zinc anode. Carbonizing this polymer under ambient conditions using a high‐power nanosecond laser forms a carbon‐coated zinc foil, which was directly utilized as the anode in aqueous zinc ion batteries. The fabricated laser‐processed PLA‐derived carbon‐coated zinc anode demonstrated an extended cycling life of almost 1600 hours, significantly outperforming the bare zinc anode. A full aqueous zinc ion battery assembled from as‐modified anode and as‐prepared V2O5 nanofibers as cathode was able to deliver a specific capacity of 238 mAh g‐1 at 1.0 A g‐1 with a capacity retention of 70 % after 1000 cycles.

On the Dendrite-Suppressing Effect of Laser-Processed Polylactic Acid-Derived Carbon Coated Zinc Anode in Aqueous Zinc Ion Batteries.

A major bottleneck limiting the commercialization of aqueous zinc ion batteries (AZIBs) is dendrite formation on the zinc anode during the plating/stripping process, which leads to rapid performance and device failure. In this regard, researchers are trying to design more stable anodes toward suppressing dendrite formation. One possible solution to tackle this problem and to extend the cycling life of AZIBs is to modify the zinc anode surface by coating carbonaceous materials, enabling controlled charge flux and uniform ion distribution. This work reports a sustainable and bio-derived polylactic acid (PLA) as a coating layer on the zinc anode. Carbonizing this polymer under ambient conditions using a high-power nanosecond laser forms a carbon-coated zinc foil, which was directly utilized as the anode in aqueous zinc ion batteries. The fabricated laser-processed PLA-derived carbon-coated zinc anode demonstrated an extended cycling life of almost 1600 hours, significantly outperforming the bare zinc anode. A full aqueous zinc ion battery assembled from as-modified anode and as-prepared V2O5 nanofibers as cathode was able to deliver a specific capacity of 238 mAh g-1 at 1.0 A g-1 with a capacity retention of 70 % after 1000 cycles.

Nanosecond pulsed laser ablation of synthetic graphite in liquids for the synthesis of spherical graphene

Pulsed laser ablation in liquids has become a simple, fast, and environmentally friendly method for the synthesis of carbon nanostructures since it does not require the use of toxic chemicals. The great advantage of this method is its ability to control the size, shape, and structure of the products by combining parameters of the laser, target material, and liquid. By ablation of two types of synthetic graphite with a high-power copper vapor laser in ethanol and distilled water, spherical graphene was obtained. The composition of the gas phase and the condensation temperature of carbon in the temperature range of 1000–5000 K were determined by means of thermodynamic modeling. The precursors for the formation of spherical graphene during laser ablation in alcohol and water are discussed.

Modeling and optimizing of laser-assisted waterjet process parameters for near-damage-free micromachining of monocrystalline silicon

Monocrystalline silicon-based microstructure functional surfaces are widely used in the field of photoelectricity. However, the traditional process is prone to damage due to the hardness and brittleness of monocrystalline silicon. In this study, the depth, width, and depth-width ratio of the micro-V-groove on the surface of monocrystalline silicon were studied using laser-assisted waterjet technology. Firstly, the nanosecond laser pulse width was optimized to minimize processing damage. Then, the response surface method (RSM) was employed to optimize the V-groove’s depth-width ratio and show the process parameters’ interactive effects. The results show that the heated affected zone (HAZ) and lattice disorder at 10 ns are significantly smaller than those at other pulse widths, and there is almost no amorphous phase on the surface of V-grooves. Single process parameter usually has different effects on the size of the V-groove, and the process parameters have significant interactive effects, which are discussed in detail in the study. According to the prediction model, the highest depth-width ratio of a V-groove is 1.39. Near-damage-free V-groove with a high depth-width ratio helps to lower the reflectivity and increase the hydrophobicity of monocrystalline silicon.

Laser processing characteristics of PCD tool and modeling analysis

Through in-depth analysis of the experimental details and forming patterns of the nanosecond laser ablation polycrystalline diamond (PCD) textured tool processing system, this study explores the microscopic morphology and dimensions of micro-pits texture on the surface of PCD tools influenced by defocus amount, laser power, and pulse frequency. Experimental results indicate that the micro-pit textures generated under different parameters exhibit diversity, including rounded structure, fragments, recast layers, and heat-affected zones. The diameter and depth of micro-pits are comprehensively affected by defocus amount, laser power, and pulse frequency, showing complex patterns. After a thorough analysis of the effects of each parameter on the texture morphology, an artificial neural network (ANN) model is introduced for the prediction of micro-pit dimensions. Through model training and optimization, accurate predictions of micro-pit diameter and depth are obtained. In comparison to traditional regression models, the ANN model demonstrates outstanding predictive performance, validating its applicability in complex machining processes. This study not only provides a profound understanding of the processing patterns of PCD textured tools but also offers an effective predictive model for the optimization and control of similar future machining processes.