Single-pulse Laser Ablation Research Articles

Dynamic laser ablation loading of a linear Paul trap

We present a detailed method for accumulating Ca+ ions controllably in a linear Paul trap. The ions are generated by pulsed laser ablation and dynamically loaded into the ion trap by switching the trapping potential on and off. The loaded ions are precooled by buffer gas and then laser-cooled to form Coulomb crystals for verifying quantity. The number of ions is controlled by manipulating the trapping potential of the ion trap, partial pressure of buffer gas and turn-on time of the entrance end cap voltage. With single-pulse laser ablation, the number of trapped ions ranges from tens to ten thousand. The kinetic energy of loaded ions can be selected via the optimal turn-on time of the entrance end cap. Using multiple-pulse laser ablation, the number is further increased and reaches about 4×104 . The dynamic loading method has wide application for accumulating low-yielding ions via laser ablation in the ion trap.

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.

Fundamental study of a femtosecond laser ablation mechanism in gold and the impact of the GHz repetition rate and number of pulses on ablation volume

In this work, we performed an experimental investigation supported by a theoretical analysis of single-shot laser ablation of gold to study the laser-matter interaction for predicting the ablation morphology and optimizing the process parameters. A set of coupled partial differential equations of the two-temperature model with dynamic optical properties and a phase explosion mechanism were used to determine the temporal and spatial evolution of the electron and lattice temperatures. The primary research focus of this work is to use the GHz frequency to investigate the ablation performance because the irradiated material is still far from thermal equilibrium during the laser-matter interaction. In contrast to conventional single-pulse laser ablation, intra-burst frequencies and the number of pulses are important factors in optimizing ablation efficiency and quality for fast material processing. Theoretical investigation revealed that the ablation volume increased due to heat accumulation, but the ablation quality decreased as the intra-burst frequencies decreased from 1000 GHz to 10 GHz. Moreover, the specific ablation volume increases with a higher burst number and lower intra-burst frequency at the expense of ablation quality.

Antireflection microstructures fabricated on the surface of a LiGaSe2 nonlinear crystal.

LiGaSe2 is a propitious material for nonlinear parametric conversion in the mid-infrared (mid-IR) range. Its refractive index of n = 2.25 in the 2-12 µm wavelength range results in significant losses due to Fresnel reflection. However, the conventional method of increasing the transmittance with antireflection coatings (ARCs) significantly reduces the damage threshold of the material. Fabrication of the antireflection microstructures (ARMs) is an alternative approach for increasing the surface transmittance. In this work, ARMs were fabricated on the surface of a LiGaSe2 crystal using a single-pulse femtosecond laser ablation method. An average transmittance of 97.2% in the 2-8 µm spectral range and the maximum transmittance of 98.6% at 4.1 µm were achieved.

Morphology modelling and validation in nanosecond pulsed laser ablation of metallic materials

Nanosecond pulsed lasers are widely used in the surface treatment of metallic materials due to their low cost and simple operation. During pulsed laser processing, many parameters such as laser and material properties are involved. Consequently, the existing mathematical models for pulsed laser ablation of metals are complex and computationally difficult. In this paper, a simple and novel model was proposed for nanosecond pulsed laser processing based on heat transfer and geometrical mathematics. The geometrical parameters functions of the recast layer under pulsed laser single ablation and continuous superimposed ablation are presented, respectively. The feasibility of the models is validated by experiments. Errors in diameter and depth of single-pulse laser ablation craters were 2.56%–7.14% and 6.82%–18.91%. The recast layer depth error is about 3.47%–12.47% for successive pulses of superimposed ablation. It predicts the shape of the recast layer on pulsed laser ablated metal surfaces. The model is a guide to the surface morphology of laser woven materials and the preparation of surface functionalities, particularly the selection of process parameters for microstructure machining.

Study of Bondable Laser Release Material Using 355 nm Energy to Facilitate RDL-First and Die-First Fan-Out Wafer-Level Packaging (FOWLP)

A thorough evaluation on selecting a bondable laser release material for redistribution layer (RDL)-first and die-first fan-out wafer-level packaging (FOWLP) is presented in this article. Four laser release materials were identified based on their absorption coefficient at 355 nm. In addition, all four of these materials possess thermal stability above 350 &#x00B0;C and pull-off adhesion on a Ti/Cu layer greater than 8 psi, further illustrating their compatibility in FOWLP. To further evaluate these materials, focus ion beam (FIB) inspection was used to examine the profile of a single-pulse laser ablation region, ensuring free penetration of 355-nm laser energy. With a designated die bonding test vehicle, die shift less than 1.5 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and rotation less than 0.02&#x00B0; before and after molding was achieved with the material bondable at temperatures lower than 200 &#x00B0;C. Furthermore, this same material required a laser energy of less than 3 W for laser release. A bondable laser release material that eliminates the requirement for a die attach material from the traditional process flow facilitates the development of cost-effective FOWLP.

Ablation efficiency of gold at fs/ps laser treatment in water and air

A comparison of single-pulse laser ablation of gold target by pulses with a 0.3–10 ps duration and a wavelength of 515 nm in air and in water was performed. The radiation was focused on the sample surface through the objectives with numerical apertures NA = 0.65 and 0.25. The influence of the medium, pulse duration, and spot size on the crater morphology was studied. A significant difference in crater morphology was found for different lenses. The ablation efficiency was studied by measuring the profiles of single-shot pulse craters using scanning force microscopy. The contribution of filamentation to the ablation process is shown quantitatively.

A critical review of the developments in molecular dynamics simulations to study femtosecond laser ablation

Laser-matter interaction is a complex physical process that has come to the forefront of scientific research, particularly due to the advancements of laser technology and its wide availability in recent decades. Studying ultrashort pulsed lasers directly through the experiments is challenging due to the short time scales involved, which could be of the order of a few picoseconds to femtoseconds. Accurate insight and knowledge about these ultrafast light-matter interactions can potentially provide valuable opportunities to advance ultra-precision manufacturing and offer more control over deterministically processing materials with ultrashort pulsed lasers. In a chronological evaluation of the scientific outputs on this matter, several research trends are noticeable. This review paper outlines the prominent trends over the years to summarise the developmental journey so far in our understanding of this complex process. We review modern developments in ultrashort pulsed laser ablation, especially the contributions of Molecular Dynamics (MD) simulations to the laser technology. We articulated the progress from analytical mathematical techniques employed in the 1990s, which facilitated widespread use of these lasers in applications ranging from medical procedures to material processing and beyond, to the advent of high-performance computing and the current focus on numerical atomistic modelling for improved real-time analysis of single pulse laser ablation. This knowledge is vital to advance the macroscopic understanding of various precision manufacturing processes relying on femtosecond lasers.

Ultrashort pulsed laser ablation of zirconia-alumina composites for implant applications

• Influence of alumina content on fs-laser machining of zirconia-alumina composites was studied. • Significant influence of material composition on material removal behavior was demonstrated. • Single phase materials have larger laser ablation thresholds and smaller material removal rate than their composites. • A lower scan speed is preferred for single phase materials while a higher scan speed is beneficial for the composites. Laser texturing of zirconia-alumina ceramics is a promising surface modification method for many applications, such as enhancing osseointegration of alumina toughened zirconia (ATZ) dental implants or improving friction behavior of zirconia toughened alumina (ZTA) hip replacement bearing components. The common problems in laser texturing of ATZ/ZTA ceramics are thermal cracking, low material removal rate (MRR), and laser-induced phase transformation (LIPT). Furthermore, the compositional variation of those ceramics will complicate these problems. In order to improve the manufacturing processability, ultrashort pulsed laser ablation behavior of ATZ/ZTA composites was investigated in this research. Single phase zirconia and alumina were found to have smaller MRRs than their composites, and this behavior was negatively correlated to the materials single-pulse laser ablation threshold. However, under multi-pulse laser irradiation, the ablation thresholds of all materials saturated to the same level, indicating that single phase materials were more sensitive to the incubation effect than their composites. This led to the MRRs of the single phase materials being reduced at larger scan speeds, while the MRRs of their composites remained independent of scan speed. It was also shown that single phase materials were less susceptible to thermal cracking than their composites under excessive heat accumulation. These results suggest that a lower scan speed is preferred for single phase materials in order to achieve a larger MRR, while a higher scan speed is beneficial for the composites for suppressing thermal cracking without compromising ablation efficiency. In addition, no LIPT was detected for zirconia dominated materials after laser ablation.

Formation of dense nanostructures on femtosecond laser-processed silicon carbide surfaces

Femtosecond (fs) laser has been proved to be a reliable tool for high-quality micromachining on silicon carbide (SiC) surfaces. In this work, we studied the formation of dense nanostructures on fs laser-processed SiC surfaces. These nanostructures are composed of lots of amorphous silicon dioxide (SiO2) nanoparticles with diameters ranging from 5 nm to 30 nm. The distribution and morphology of the formed nanostructures are primarily affected by the laser pulse energy, the laser scanning velocity, and the laser repetition rate. Under specific parameters, the width of the nanostructure area is more than five times wider than the width of the prepared microgrooves. We also observe the expansion of plasma plumes produced upon single-pulse laser ablation by a microscopic imaging system equipped with an intensified charge-coupled device (ICCD) camera to explain the formation mechanisms. We propose that the dense nanostructures are formed due to the high-temperature decomposition, assembling, and oxidation of the laser ablation products. The effective accumulation of laser-ablated products above the laser-irradiated areas is the key to their formation.

Single-pulse femtosecond laser ablation of monocrystalline silicon: A modeling and experimental study

In this paper, a visualization model by using the COMSOL® Multiphysics was established to investigate the quantitative relationship between the parameters of the single-pulse femtosecond laser and the geometries of the ablated monocrystalline silicon micro-holes. Monocrystalline silicon was ablated with different femtosecond laser single-pulse energies and the diameters as well as the depths of the obtained micro-holes were compared with the prediction results of the established visualization model. The comparison results have demonstrated that the single-pulse femtosecond laser ablation results can be predicted effectively based on the established visualization model. The prediction error of the ablated micro-hole diameter and depth were within 2.31% and 15.40%, respectively, without any prior optimization experiments. It is thus possible to precisely conduct femtosecond laser ablation on monocrystalline silicon for desired geometries by utilizing appropriate parameters without trial-and-errors as in traditional femtosecond laser ablation technologies.

Ultrashort single-pulse laser ablation of stainless steel, aluminium, copper and its dependence on the pulse duration

In this work, we investigate single-pulse laser ablation of bulk stainless steel (AISI304), aluminium (Al) and copper (Cu) and its dependence on the pulse duration. We measured the reflectivity, ablation thresholds and volumes under the variation of pulse duration and fluence. The known drop of efficiency with increasing pulse duration is confirmed for single-pulse ablation in all three metals. We attribute the efficiency drop to a weakened photomechanically driven ablation process and a stronger contribution of photothermal phase explosion. The highest energetic efficiency and precision is achieved for pulse durations below the mechanical expansion time of 3-5 ps, where the stress confinement condition is fulfilled.

Exploiting calibration free laser-induced breakdown spectroscopy (CF-LIBS) for the analysis of food colors

The present study report the elemental concentration of different brands of food colors using calibration free laser induced breakdown spectroscopy (CF-LIBS). The laser induced plasma was produced on the surface of pelletized food colors using single and double pulse laser ablation and the plasma emissions were recorded with LIBS 2500+ spectrometer. The validity of local thermodynamic equilibrium LTE was confirmed using Mc. Whirter’s criteria. The emission spectra were qualitatively analyzed which detected seventeen elements in food color samples. The quantitative analysis was performed using plasma parameters and line emission intensities in CF-LIBS algorithm. The analysis shows that H, C, N, O, and Na are present as major elements, whereas Mg, Al, Si, K, Ca, Cr, Mn, Fe, Zn, Sr etc. are detected in trace amount in food colors.

Fabrication of an antireflection microstructure on AgClBr polycrystalline fiber by single pulse femtosecond laser ablation

Polycrystalline infrared (PIR) fibers are used for numerous applications, one of those being power delivery for CO2 −lasers. However, the fiber tip surface’s transmittance cannot be increased with conventional antireflection coatings due to the surface unevenness. Antireflection microstructures (ARMs) offer an alternative way of increasing transmittance. In this work, ARMs were fabricated on the fiber tip surface of an AgClBr fiber by single-pulse femtosecond laser ablation. A single-surface transmittance of 92.8% at 10.6 µm, a CO2 −laser operation wavelength, was achieved. The proposed method can help significantly improve the systems’ efficiency, where power delivery for CO2 −lasers or sources operating in the wide wavelength range is required.

Sub-picosecond single-pulse laser ablation of the CrMnFeCoNi high entropy alloy and comparison to stainless steel AISI 304

In recent years, high entropy alloy research has experienced increased interest and it was found that some of these materials have extraordinary properties. High entropy alloys also show an increased damage resistance to high-energy particle irradiation, mainly due to effects caused by the increased configuration entropy. So far, no detailed studies have been carried out regarding the interaction with high-energy electromagnetic radiation, particularly by means of lasers. In this work, we compare results of ultrashort-pulse laser-matter interaction of the CrMnFeCoNi alloy (Cantor alloy), the most researched representative of this material group, with the conventional alloy stainless steel AISI304. Since metals can in general be processed efficiently with ultrashort pulses, which is of particular interest for industrial applications, we performed our experiments with single infrared sub-picosecond pulses. The crater surface morphology and process energetics are discussed in detail and the validity of established ablation models is investigated. We find that the damage threshold of the CrMnFeCoNi alloy is slightly lower than that of AISI304 and consequently CrMnFeCoNi alloy shows an increased ablation volume. Therefore, the high entropy alloy CrMnFeCoNi can be processed efficiently with ultrashort-pulse lasers.

Single-pulse laser ablation–inductively coupled plasma–mass spectrometry U–Pb dating of thin zircon rims: An application to metamorphic rocks from Mount Everest, eastern Nepal

This study describes an improved method for U–Pb dating of external zircon surfaces using laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS). Single-pulse LA of zircons mounted in Teflon by Excimer and femtosecond lasers produced age–depth profiles with 0.1 μm resolution. Application of this technique to samples from the Higher Himalayan Crystallines, Mount Everest region, eastern Nepal, revealed outer rims with ages of 15 ± 1 Ma. Most of these rims were not visible on cathodoluminescence images of polished cross-sections of the grains.

Fabrication of antireflection microstructures on the surface of GaSe crystal by single-pulse femtosecond laser ablation.

GaSe crystals are promising as nonlinear optical converters in the mid- and far-IR ranges. However, it is challenging to increase the GaSe surface transmittance of 77% with conventional antireflection coatings because of poor surface quality, leading to coating adhesion problems. Antireflection microstructures (ARMs) offer an alternative way of increasing surface transmittance. In this work, ARMs were fabricated on the surface of a GaSe plate by single-pulse femtosecond laser ablation. An average GaSe surface transmittance of 94% in the 7-11 µm range and a maximum transmittance of 97.8% at 8.5 µm were obtained. The proposed method can be used to increase the efficiency of GaSe-based nonlinear converters.

Picosecond laser ablation of metals and semiconductors with low-transverse order Gaussian beams

Picosecond pulse duration laser–material interactions are extremely complex and much less studied than the physics of femtosecond and nanosecond ablation. Additionally, multimode laser beam structure can inhibit robust analysis and comparisons of effects at any pulse duration. To address these gaps, single-pulse laser ablation of Al, Si, Ti, Ge, and InSb in air and Ge in vacuum was studied using low-transverse order Gaussian beams at a 1064 nm wavelength and 28 ps pulse duration. Crater depths of 0.4 to 6.3 μm and volumes of up to 4000 μm3 were measured using a laser confocal microscope. Crater depths plateau with increasing fluence and are slightly higher for Ge in vacuum than in air. Crater volume increases linearly with fluence for all materials in air. In vacuum, the volume of material above the surface was less than in air and increased at a lower rate with increasing fluence. The ratio of volume above the surface (due to melt flow and redeposition) to volume below the surface plateaus for all materials to ∼0.7 in air and 0.4 for Ge in vacuum. The ablation efficiency, defined as atoms removed per incident photon, was higher at low fluences and decreased to ∼0.004 for all materials at higher fluences. Simulations using the directed energy illumination visualization tool showed that bulk melt flow out of the crater caused by the evaporation recoil pressure dominated at higher fluences. Plateauing of crater depth with fluence was caused by melt reflow into the crater, which effects smaller crater widths more than larger ones, as evidenced by comparing multimode results with TEM00 simulations. Recondensation of evaporated material was identified as the main difference between craters formed in air versus vacuum, and the Knudsen layer jump conditions in DEIVI were modified to account for an estimated ≈20 % recondensation rate. The simulations showed a resulting reduction in evaporation, which created less recoil pressure, driving less melt out of the crater. The results of this study help elucidate mass removal mechanisms in the picosecond pulse duration regime and their dependence on laser and environmental characteristics.

Rapid synthesis and characterization of advanced ceramic-polymeric nanocomposites for efficient photocatalytic decontamination of hazardous organic pollutant under visible light and inhibition of microbial biofilm

Ceramic-polymeric 3C–silicon carbide-graphitic carbon nitride (3C–SiC@g-C3N4) nanocomposites were synthesized by decorating cubic phased, ceramic 3C-Silicon carbide (3C–SiC) on the framework of the nanosheets of metal free polymeric graphitic carbon nitride (g-C3N4) by single step pulsed laser ablation in liquid (PLAL) method. Morphological, structural, elemental and optical characterizations of the synthesized 3C–SiC@g-C3N4 nanocomposites were carried out. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) studies confirm the perfect anchoring of 3C–SiC on g-C3N4 nanosheets in 3C–SiC@g-C3N4 nanocomposites synthesized by PLAL method. Ultra-violet diffuse reflectance spectra (UV-DRS) of 3C–SiC@g-C3N4 indicated the enhancement of visible light absorption and also the narrowing down of band gap energy in 3C–SiC@g-C3N4 nanocomposites, as a result of the anchoring of 3C–SiC on g-C3N4. Also we noticed the decrease of photoluminescence (PL) emission intensities in the PL spectra of 3C–SiC@g-C3N4 with respect to pure g-C3N4, which indicates the reduced photo-induced charge recombination by the presence of 3C–SiC content on g-C3N4 nanosheets. In the application side, PLAL synthesized 3C–SiC@g-C3N4 nanocomposites exhibited enhanced visible light driven photocatalytic degradation of methylene blue dye in water, improved antibacterial activity against Pseudomonas aeruginosa (gram-negative) and Staphylococcus aureus (gram-positive) bacteria, and also served as better inhibiting agent for biofilm formation, compared to pure g-C3N4 nanosheets. It is quite obvious from our studies that this ceramic-polymeric nanocomposite, 3C–SiC@g-C3N4 has the potential application for antibacterial and anti-biofilm activities in addition to its remarkable photocatalytic performance.

Impulse of planar and sphere target by nanosecond laser ablation in a large beam spot

We investigated an ablation impulse irradiated by a nanosecond laser with an Al planar and sphere target in a large beam spot. A torsion pendulum was developed to investigate single pulsed laser ablation impulses. A beam spot size of about 1 mm diameter was selected as the large spot size because investigations have proved that a beam spot size less than 420 μm satisfied a one-dimensional plume expansion model. The results show that the minimum laser fluence corresponding to an observable ablation impulse of a planar target is about 3 J cm−2, and the optimum laser fluence corresponding to the highest impulse coupling coefficient is about 10 J cm−2 for both large and small beam spots. Our investigations prove that these two parameters are independent of the beam spot size. The impulse investigation of a sphere-shaped target reveals that its overall impulse is lower than that of a planar one irradiated by a large laser beam spot in high laser fluence regimes, especially when a strong plasma plume event is happening. This phenomenon may be caused by different plasma plume propagation directions due to a non-flat surface of the sphere targets because the plume expansion by nanosecond laser ablation is mainly normal to the local surface.