Nanosecond Laser Pulses Research Articles

Study on the influence of side-blown airflow velocities on plasma and combustion wave generated from fused silica induced by combined pulse laser

This study examines the impact of variations in side-blowing airflow velocity on plasma generation, combustion wave propagation mechanisms, and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser. The airflow rate and pulse delay are the main experimental variables. The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing. The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the side-blowing airflow at different airflow rates (0.2 Ma, 0.4 Ma, and 0.6 Ma). As the flow rate of the side-blow air stream increases, the initial expansion velocities of the plasma and combustion wave gradually decrease, and the side-blow air stream increasingly suppresses the plasma. It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action. Therefore, the side-blown airflow alone cannot completely clear the plasma. Depending on the delay conditions, the pressure of the side-blowing airflow, the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser. Both simulation and experimental results are consistent, indicating the potential for further exploration of fused silica targets in the laser field.

Dual‐Stoichiometry Copper Sulphide Nanoparticles by Laser Ablation in DMSO: Synthesis and Biomedical Applications for Enhanced Photothermal Therapy and Photoacoustic Imaging

AbstractCopper sulphide nanoparticles are synthesized by laser ablation of a copper target in DMSO by a 527 nm nanosecond pulsed laser. These nanoparticles have double stoichiometry (CuS and Cu1.8S) and crystalline structures, sizes under 30 nm, and they present substantial absorbance in the second near‐infrared window and photoluminescence in the visible region. The nanoparticles are used as photothermal and photoacoustic agents at 1080 nm and 1064 nm, respectively. Utilizing as a photothermal agent, these nanoparticles rapidly exhibit local heating, photothermal stability, and a temperature change of 52.2 °C within 300 s at 1 mg mL−1 concentration and 3.23 W cm−2 laser intensity. On the other hand, while employed as a photoacoustic agent, they enhanced the contrast significantly and increased the brightness proportional to their concentrations when compared to ultrasound imaging. Additionally, the biocompatibility properties of these nanoparticles were tested with cancer cells, and they were subjected to laser ablation to assess their photothermal effects. In this article, we demonstrate that copper sulphide nanoparticles synthesized by pulsed laser ablation hold great promise for photothermal and photoacoustic applications, especially in biomedical applications.

High-Precision Photoacoustic Neural Modulation Uses a Non-Thermal Mechanism.

Neuromodulation is a powerful tool for fundamental studies in neuroscience and potential treatments of neurological disorders. Both photoacoustic (PA) and photothermal (PT) effects are harnessed for non-genetic high-precision neural stimulation. Using a fiber-based device excitable by a nanosecond pulsed laser and a continuous wave laser for PA and PT stimulation, respectively, PA and PT neuromodulation is systematically investigated at the single neuron level. These results show that to achieve the same level of neuron activation recorded by Ca2+ imaging, the laser energy needed for PA stimulation is 1/40 of that needed for PT stimulation. The threshold energy for PA stimulation is found to be further reduced in neurons overexpressing mechano-sensitive channels, indicating direct involvement of mechano-sensitive channels in PA stimulation. Electrophysiology study of single neurons upon PA and PT stimulation is performed by patch clamp recordings. Electrophysiological features induced by PA are distinct from those by PT, confirming that PA and PT stimulation operate through different mechanisms. These insights offer a foundation for the rational design of more efficient and safer non-genetic neural modulation approaches.

Discrimination of cow, goat, and sheep milk by femtosecond and nanosecond laser-induced breakdown spectroscopy

In the present work, femtosecond Laser Induced Breakdown Spectroscopy, fs-LIBS, is applied for the first time for the analysis of the inorganic content and the identification of the animal origin of milk samples (i.e., cow, goat, and sheep). The fs-LIBS spectra were analyzed by different machine learning algorithms (i.e., multivariate statistical analysis), and their performance was assessed. The obtained classification accuracies of the milk samples based on the animal origin were found to attain values up to 95 %, depending on the algorithm used. For comparison purposes, LIBS experiments were also carried out employing nanosecond laser pulses, ns-LIBS. The obtained results from both the fs- and ns-LIBS experiments were found to be in excellent agreement between them. The present findings, using fs laser excitation, demonstrate and extend the capabilities of LIBS technique, for the identification of the animal origin of milk samples, thus making fs- and/or ns-LIBS technique a powerful and useful tool for milk authentication, quality, and safety control related research.

Nanosecond laser induced periodic silicon microstructures for broadband antireflective applications

Laser-driven micro/nano-texturing is a remarkably efficient and cost-effective technique, having diverse applicability in the realm of photonics, optoelectronics, and photovoltaics. Here, we demonstrate the high-intensity nanosecond laser-matter interactions for periodic micro/nanostructures on silicon, exclusively to emphasize the effects of laser parameters for large-scale integration. A wide range of periodic structure rapid fabrication over a wafer level is systematically studied for optimised parameters using nanosecond laser pulses (1064 nm, 50 ns) at different pulse repetition rates ranging from 10 to 40 kHz. A comprehensive understanding based on physical, structural, and optical studies reveals a strong correlation between the formation of nano/microstructure morphology and the laser parameters. The laser-matter interactions result in trench-like periodic patterns, formation of nanostructure agglomerations as light-trap-centres on the silicon surface. Such nano/micro periodic structures provide a dominant reduction in reflection losses of up to 80 % over a broad UV-NIR spectral region. The studies further demonstrate that the periodic structural patterns could also be potentially utilised for large-scale optical diffraction applications. In addition, the extra layer coating of Silicon Nitride (Si3N4) on the textured silicon further reduces the reflection losses, which is an added advantage of integrated silicon technology. The present work could open a commercial pathway for the rapid fabrication of nanosecond laser-based nanotexturing and periodic grating structures, enabling significantly reduced reflection and improved light trapping in large-scale Silicon-based applications due to its speed, repeatability, and high precision.

Simultaneous improvement in surface quality and hardness of laser shock peened Zr-based metallic glass by laser polishing

Laser shock peening (LSP) is an effective method to improve the plasticity of metallic glasses (MGs) but it also deteriorates the surface quality and decreases the surface hardness, which in turn hinders the applications of MGs. Accordingly, this study was attempted to achieve the simultaneous improvement in surface quality and hardness of LSPed Zr-based MG by nanosecond pulsed laser polishing. LSP of the MG was firstly performed by using a high-energy pulsed laser to prepare the LSPed MG samples, and then laser polishing of the LSPed MG surface was conducted by using nanosecond pulsed laser. The effects of laser polishing parameters (i.e., average laser power, scanning speed, overlap rate, and number of irradiation cycle) on the surface quality and hardness of the LSPed MG were investigated in detail. The experimental results showed that after laser polishing under specific conditions, a 90% reduction in surface roughness and a 11 % increase in surface hardness could be achieved for the LSPed MG surface. This study provides a simple and effective method to simultaneously improve the surface quality and hardness of LSPed MGs, which would be of great significance for the practical engineering applications of MGs.

Non-contact targeted removal of remnant powder particles from additive manufacturing builds with nano-second laser pulsing

Post-production precision cleaning is one critical challenge in Additive Manufacturing (AM) production of high-value, critical parts/builds. A part shedding particle during its operational use could cause severe complications in critical applications such as medical devices and aerospace components. This study presents a non-contact precision particle removal procedure based on a novel Dry Laser Cleaning (DLC) framework. DLC utilizes the thermo-elastic wave generation/propagation and high-frequency surface acceleration fields to dislodge and remove remnant particles due to inertial forces from a well-defined (user-specified) cleaning zone in a non-contact manner, as opposed to cleaning the entire build surface, which could lead to undesirable re-deposition and re-location of particles as well as high cost. The removal of spherical Stainless Steel 316 L (SS316L) micro-particles commonly used in AM from polished, atomically flat Silicon (Si) wafer substrates with uniform high free surface energy using a nano-second laser pulse is experimentally and computationally investigated. In general, a rough surface has a lower average free surface energy; thus, its cleaning, compared to Si wafer, is less challenging. The data with the SS316-Si material pair offers a consistent baseline. In parallel to experiments, a fully-coupled thermo-mechanical finite element study is also conducted for transient surface acceleration simulations to predict the effectiveness of SS316L micro-particle removal from a Si wafer substrate with laser pulsation. It is observed that SS316L micro-particles with a diameter larger than 5.61 μm, 8.43 μm, and 12.24 μm can be removed entirely at 3 mm, 6 mm, and 9 mm distances from its epicenter, respectively. Accordingly, a work-of-adhesion of 990.8 mJ/m2 is selected between the SS316-Si material pair, consistent with the literature. The reported experiments and simulations demonstrate the potential of the proposed rapid precision particle removal procedure for cleaning critical powder-based AM builds, where the targeted removal of particles is essential for the safe and reliable operation of high-value builds and parts.

Solid-to-plasma transition of polystyrene induced by a nanosecond laser pulse within the context of inertial confinement fusion.

Laser direct drive (LDD) inertial confinement fusion (ICF) involves irradiating a spherical target of thermonuclear fuel coated with an ablator, usually made of polystyrene. Laser energy absorption near the target surface leads to matter ablation, hydrodynamic shocks, and ultimately capsule implosion. The conservation of spherical symmetry is crucial for implosion efficiency, yet spatial modulations in laser intensity can induce nonuniformities, causing the laser imprint phenomenon. Understanding laser imprint, especially considering the initial solid state, is essential for advancing LDD ICF. A first microscopic model of solid-to-plasma transition was built in 2019, accounting for laser absorption in the solid state with a band-structure-based ionization model. This model has been improved to include chemical fragmentation and a more accurate description of electron collision frequency in various matter states. The latest development involves assessing the model's reliability by comparing theoretical predictions with experimental observations. Despite the success of this approach, questions remain, leading to further investigations and observations under different irradiation conditions. This work presents an experiment with a nanosecond pulse, taking into account hydrodynamic effects, and measures transmission dynamics over the entire laser beam area to observe two-dimensional effects. The objective is to adapt the theoretical model, couple it with a hydrodynamic code, and observe additional effects related to the initial solid state.

Nonlinear energy absorption during optical breakdown in bulk dielectrics

Portion of energy employed by a single, tightly focused laser pulse in various transparent dielectrics was demonstrated versus the incident energy fluence or alternatively, intensity. The measurements were conducted for both the femtosecond and nanosecond laser pulses. Moreover, the energy scattered during the long-lived breakdown process was estimated within the integrating sphere. It appeared that the recorded strongly non-linear dependence of absorptance on the energy fluence (intensity) can be well approximated by the sigmoidal Hill function. The stationary points of the absorptance curve were used to determine threshold-like values characterizing breakdown development. In this way, we defined threshold for the non-linear absorption which can be considered as an empirical laser-induced breakdown threshold (LIBT). Additionally, the fitting parameters of the experimental data substantiated the absorption character for short and long laser pulses.

Control under optical, nonlinear optical and kinetic properties of two-dimensional gradient CdSe1-xSx nanocrystals

Peculiarities of photoluminescence (PL) and absorption spectra of gradient nanocrystals CdSe1-xSx colloidal solution were studied by pump and probe technique under stationary excitation of excitons by nanosecond laser pulses. The PL peaks and differential transmission peaks positions changing were revealed with the CdSe1-xSx nanocrystals composition variation. Bleaching of excitons transitions was observed for high pump intensities and explained by excitons space filling effect. The changing of the differential transmission peaks positions was explained by the nanocrystal band gap dependence on the chemical composition. Time-resolved PL measurements from the sub-picoseconds to tens of nanoseconds range demonstrated a strongly different behavior for gradient nanocrystals and pure CdSe nanocrystals. For pure nanocrystals two typical time-scales were resolved contrary to the gradient nanocrystals where (with the growth of sulfur concentration) only a single time scale was revealed. The observed modification of time-resolved PL for gradient nanocrystals is caused by the presence of traps in the gradient samples due to the chemical composition modification.

Drop-on-demand bioprinting: A redesigned laser-induced side transfer approach with continuous capillary perfusion

We present a drop-on-demand (DOD) bioprinting method based on a novel implementation of laser-induced side transfer (LIST). Our approach involves continuous bioink perfusion through a glass capillary featuring a laser-machined hole in the capillary wall, serving as a nozzle. Focused low-energy nanosecond laser pulses are employed for precise droplet ejection. This innovative design separates the control of the bioink flow rate inside the capillary from the printing rate (drop ejection), leading to an enhanced printing workflow. We assessed the impact of key printing parameters, such as laser energy and flow conditions, on printing quality. Furthermore, we utilized the redesigned LIST to bioprint human umbilical vein endothelial cells (HUVECs). Our findings indicate that the printed HUVECs exhibit no viability loss and demonstrate the ability to recruit perivascular cells, including pericytes and fibroblasts. The redesigned LIST can be utilized in tissue engineering applications requiring DOD cell printing.

Experimental Parametric Investigation of Nanosecond Laser-Induced Surface Graphitization of Nano-Crystalline Diamond.

While nano-crystalline diamond (NCD) is a promising engineering composite material for its unique mechanical properties, achieving the ultrahigh surface quality of NCD-based components through conventional grinding and polishing is challenging due to its exceptional hardness and brittleness. In the present work, we experimentally investigate the nanosecond laser ablation-induced graphitization characteristics of NCD, which provides a critical pretreatment method of NCD for realizing its superlative surface finish. Specifically, systematic experimental investigations of the nanosecond pulsed laser ablation of NCD are carried out, in which the characteristics of graphitization are qualitatively characterized by the Raman spectroscopy detection of the ablated area of the microhole and microgroove. Subsequently, the influence of laser processing parameters on the degree and morphological characteristics of graphitization is evaluated based on experimental data and related interpretation, from which optimized parameters for maximizing the graphitization of NCD are then identified. The findings reported in the current work provide guidance for promoting the machinability of NCD via laser irradiation-induced surface modification.

Generation of Wide Color Gamut in a Collisional and Magnetized Plasma by Laser‐Induced Coloration on Composite Structure Surfaces

AbstractIn this paper, a new scheme for generating a wide gamut of structural colors on the thin‐film‐stack‐based (TFSB) substrates is proposed. The TFSB surfaces consist of titanium/random gold nanoparticles (AuNPs) and titanium/ random gold and copper nanoparticles (Au+CuNPs), which can trigger more resonance absorption and widen the color gamut. The electric fields in two designed structures are simulated, and the results showed that the random distribution of AuNPs and Au+CuNPs enhance the uniform local surface plasmon resonance (LSPR) response. This enhancement is crucial in broadening the coverage of the reflection spectrum, which enables the generation of a wide range of colors, including green and red. The influence of laser parameters on the color of TFSB substrates and tested their durability in terms of time is analyzed. Finally, a color palette and made structural color patterns on TFSB by nanosecond pulsed laser are prepared. The proposed new scheme can be easily fabricated by magnetron sputtering without requiring additional procedures, which can open new perspectives in plasmonic colors. This work demonstrates that the promising potential of methods in creating a wide color gamut on metallic surfaces. Additionally, it serves as a means to store information for the preservation and protection of traditional cultures.

High-Performance Bioinspired Hierarchical Microgroove Wick for Ceramic Vapor Chambers Achieved by Nanosecond Pulsed Lasers.

Directly integrating ceramic vapor chambers into the insulating substrate of semiconductor power devices is an effective approach to solve the problem of heat dissipation. Microgrooves that could be machined directly on the shell plate without contact thermal resistance and mechanical dislocation offer exciting opportunities to achieve high-performance ceramic vapor chambers. In this study, a bioinspired hierarchical microgroove wick (BHMW) containing low ribs via one-step nanosecond pulsed laser processing was developed, as inspired by the Sarracenia trichome. The superwicking behavior of microgrooves with different structural parameters was investigated using capillary rise tests and droplet-spreading experiments. The BHMW exhibited excellent capillary performance and anisotropic hemiwicking performance. At a laser scanning spacing of 30 μm, the BHMW achieved a capillary wicking height of 114 mm within 20 s. The optimized BHMW demonstrated a capillary parameter (ΔPc·K) and an anisotropic hemiwicking ratio of 4.46 × 10-7 N and 11.93, respectively, which were 1182 and 946% higher than references, as achieved through nanosecond pulsed laser texturing under identical parameters. This work not only develops a high-performance hierarchical alumina microgroove wick structure but also outlines design guidelines for high-performance ceramic vapor chambers for thermal management in semiconductor power devices.

Investigation of ablation efficiency and properties of silicon carbide nanoparticles synthesised using pulsed laser ablation in liquid

This study optimised the synthesis and ablation efficiency of 3C silicon carbide (SiC) nanoparticles (NPs) using nanosecond pulsed laser ablation in liquid for electronic and biomedical applications. Various process parameters, including laser fluence, scanning speed, and ablation time, were systematically varied to assess their impact on ablation efficiency and NP properties. Statistical analysis identified optimal conditions: a 15 min ablation time, 0.5 m/s scanning speed, and 7.5 J/cm² laser fluence with the maximum mass productivity of 1.196 mg.h−1W−1. Characterisation techniques, including UV-Vis, Dynamic Light Scattering (DLS), FESEM with EDX, FTSEM, and XRD, confirmed that higher laser fluence, scanning speed, and ablation time increased colloid concentrations without altering NP shape or size. XRD analysis verified the phase composition as 3C SiC, with DLS showing smaller NP sizes than image analysis. The results also suggested that increasing the NP size decreased the optical band gap. A direct correlation was found between ablated mass and colloid concentration.

Rewritable Photonic Integrated Circuit Canvas Based on Low-Loss Phase Change Material and Nanosecond Pulsed Lasers.

Programmable photonic integrated circuits (PICs) are an increasingly important platform in optical science and engineering. However, current programmable PICs are mostly formed through subtractive fabrication techniques, which limits the reconfigurability of the device and makes prototyping costly and time-consuming. A rewritable PIC architecture can circumvent these drawbacks, where PICs are repeatedly written and erased on a single PIC canvas. We demonstrate such a rewritable PIC platform by selective laser writing a layer of wide-band-gap phase change material (PCM) Sb2S3 with a low-cost benchtop setup. We show arbitrary patterning with resolution up to 300 nm and write dielectric assisted waveguides with a low optical loss of 0.0172 dB/μm. We envision that using this inexpensive benchtop platform thousands of PIC designs can be written, tested, and erased on the same chip without the need for lithography/etching tools or a nanofabrication facility, thus reducing manufacturing cost and increasing accessibility.

Quantitative analysis of laser-generated ultrasonic wave characteristics and their correlation with grain size in polycrystalline materials

Abstract The quantitative relationship between nanosecond pulsed laser parameters and the characteristics of laser-generated ultrasonic waves in polycrystalline materials was evaluated. The high energy of the pulsed laser with a large irradiation spot simultaneously generated ultrasonic longitudinal and shear waves at the epicenter under the slight ablation regime. An optimized denoising technique based on wavelet thresholding and variational mode decomposition was applied to reduce noise in shear waves with a low signal-to-noise ratio. An approach for characterizing grain size was proposed using spectral center frequency ratio (SCFR) based on time-frequency analysis. The results have demonstrated that the generation regime of ultrasonic waves is not solely determined by the laser power density; even at high power densities, a high energy with a large spot can generate an ultrasonic waveform dominated by the thermoelastic effect. It is ascribed to the intensification of the thermoelastic effect with the proportional increase in laser irradiation spot area for a given laser power density. Furthermore, both longitudinal and shear wave SCFRs are linearly related to grain size in polycrystalline materials; however, the shear wave SCFR is more sensitive to finer-grained materials. This study holds great significance for evaluating metal material properties using laser ultrasound.

Development of laser structured three-dimensional patterns for improved wettability and performance of electrodes for lithium-ion batteries

The demand for improved performance and higher energy density of LIBs is growing due to their wide range of applications and advancement in the energy storage market for electric vehicles. Three-dimensional (3D) structured electrodes have recently been considered the best and most promising approach to improve battery performance as they exhibit high areal and specific capacity. In the work described here, a nanosecond pulsed fiber laser was used to generate four types of surface patterns named: line, grid, triangular end, and rectangular end patterns with an equal amount of ablated active material volume. A study on wettability was performed using the spread area, wetting time, wetting balance, and capillary rise measurements. Moreover, the Lucas Washburn and extended wettability models were used to quantitatively express the wetting behavior using the term wetting rate. In all approaches, line-patterned electrodes show better wettability along with a higher wetting rate, while poor behavior is seen with an unstructured electrode. Galvanostatic tests were used to examine how these electrode surface patterns influence the electrochemical performance of the battery. The capacity retentions, discharge capacity efficiencies, and cyclic stabilities were improved on cells with line, triangular end, and rectangular end patterned electrodes.

Single‐crystalline indium selenide fibers by laser‐induced recrystallization and their tunable whispering‐gallery‐mode lasing by pressure‐modulating

AbstractIndium selenide (InSe) crystal, as an emerging Van der Waals semiconductor, showed great potential in optical and optoelectronic devices due to its remarkable electron mobility, flexible direct bandgap, and photoresponsivity. Especially, the bulk single‐crystalline InSe shows superplastic deformability with the aid of the interlayer gliding and cross‐layer dislocation slip. The extraordinary mechanical behavior brings significant opportunities and possibilities to pressure‐modulated optical devices, which, however, have not been explored sufficiently. Additionally, InSe crystals are challenged in the rapid large‐scale preparation and reproduction due to limitations, such as phase heterogeneity, dissociation risks, and chemical instability. Herein, we proposed a fiber drawing technique to create single‐crystalline InSe by the molten core drawing method combined with CO2 laser‐induced recrystallization. The fabricated InSe fiber, spanning several meters in length, shows a uniform and directional single‐crystalline InSe core encased within a 450 µm thick protective borosilicate glass cladding. The inherent core‐cladding configuration of the InSe fibers not only provides robust protection to the InSe crystals but also seamlessly creates a whispering‐gallery‐mode microcavity. Utilizing a 532 nm nanosecond pulsed laser as a pump, a tunable lasing from 1076.2 to 1111.8 nm was achieved, dictated by the controlled pressure within the InSe fiber. We present a simple and effective method for single‐crystalline InSe fabrication and first achieve a pressure‐modulated laser in a near‐infrared band based on InSe fiber, heralding an advancement for the scalable, efficient generation of tunable lasers.

High-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser operating at 1.7 µm

We report on a high-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser at 1.7 µm. Driven by an acousto-optically Q-switched 1314 nm two-crystal Nd:YLF laser, the highly efficient cascaded YVO4 Raman laser at 1715nm was obtained within the well-designed L-shaped resonator. Thanks to the absence of spatial hole burning in the stimulated Raman scattering process, significant spectral purification of second-Stokes radiation was observed by incorporating a fused silica etalon in the high-Q fundamental cavity. Under the repetition rate of 4 kHz, the highest average output power for single longitudinal mode operation was up to 2.2 W with the aid of precision vibration isolation and precision temperature controlling, corresponding to the pulse duration of ∼2.8 ns and the spectral linewidth of ∼330 MHz. Further increasing the launched pump power, the second-Stokes laser tended toward be always multimode, and the maximum average output power amounted to 4.8 W with the peak power of ∼0.8 MW and the spectral linewidth of ∼0.08 nm. The second-Stokes emission was near diffraction limited with M2 < 1.4 across the whole pump power range.