Continuous Wave Laser Ablation Research Articles

Assessment of continuous laser ablation model for lightweight quartz fiber reinforced phenolic composite

AbstractA comprehensive investigation into the interaction between a continuous wave (CW) laser and lightweight quartz fiber reinforced phenolic (LQFRP) composite would provide valuable insights into the characteristics and performance of ablation. To simulate the CW laser ablation of LQFRP composite, a 2D symmetrical element model was developed, incorporating the heat conduction equation, resin pyrolysis mechanism, and deformed geometry module. This model was the first to examine the internal pyrolysis degree and gas flow field of LQFRP composite under CW laser irradiation, and its predictions were in reasonable agreement with experimental measurements. Additionally, the model was used to simulate CW laser ablation with varying spot sizes and power densities. The results revealed that during the laser ablation process, an internal high‐pressure zone formed on the side of the ablation hole. The volatilization of SiO2 was identified as the dominant dissipation mechanism for material removal. The width of the ablation hole was positively correlated with the laser spot size, while the depth of the ablation hole was positively correlated with the laser power density.Highlights The model first studied the internal pyrolysis degree and flow field of LQFRP composite under laser irradiation. The volatilization of SiO2 was identified as the dominant dissipation mechanism for material removal. An internal high‐pressure zone formed on the side of the ablation hole during the laser ablation process. The width of the ablation hole was positively correlated with the laser spot size, while the depth of the ablation hole was positively correlated with the laser power density.

New method of continuous-wave laser ablation for processing microgroove with variable cross-section

Surface microgrooves can effectively reduce the drag and have unparalleled advantages in energy saving and environmental protection. In the fabrication of microgrooves, the laser processing has shown a broad prospect in the fabrication of microgrooves for the advantages of high processing efficiency, no tool wear, no processing stress, etc. However, under the given process parameters, the energy distribution of the laser spot is fixed, and it is difficult to achieve different cross-sectional shapes in a single microgroove, which may have better performance for the drag reduction. In this situation, the effect of variable cross-section microgrooves on the drag reduction is demonstrated and the drag reduction mechanism is analyzed through the fluid simulation. Further, a novel method, moving zoom laser processing, is proposed to realize the fabrication of microgrooves with variable width at equal depth. For orderly planning of the laser processing parameters, the continuous wave laser (CW laser) ablation model is established under ‘tight focusing’ arrangement with predicted microgroove profiles, and the prediction errors of the model for the width and depth are 4.53 μm and 6.77 μm, respectively. Then, the ablation model is extended to the defocusing condition, and the prediction errors of the width and the depth of the microgroove under defocus arrangement are less than 3 % and 9 %, respectively. Additionally, the planning method of the process parameters in the moving zoom laser processing is introduced. Finally, the feasibility of the proposed method is verified experimentally and the microgroove with a depth of 24 μm and a width of 165–231 μm is successfully fabricated by the proposed method. With the proposed processing strategies, a good and concerned reference is provided for drag reduction technology with surface microgroove.

High-energy continuous wave laser ablation of alumina ceramic

The development of high-energy continuous wave (CW) laser has enabled the generation of output powers ranging from 300 to 500 kW. Understanding the ablation mechanism of CW lasers at high laser fluence is crucial for the design of effective high-energy laser protection materials. We note that the particle-like impurities present in the protective coating material can induce defects on the ceramic-like target surface during high-energy CW laser ablation, which can alter the laser absorptivity and manifest a completely different ablation mechanism. Here, we systematically investigate the mechanism of high-energy CW laser ablation of alumina ceramic, with a specific focus on the roles of defect induction, energy transfer, and impact sputtering in the dynamic ablation of target. Specifically, the transient processes between high-energy CW laser and ceramic target will be investigated in terms of the evolution results of the ablation region, the microscopic characteristics of the ablated material, the high time-resolved on-line monitoring, and the multiphase hydrodynamics simulation. Finally, the transparent property of molten alumina ceramic to laser is proved to allow for penetrating damage to ceramic-metal composites.

Carbon nanotube sponges filled sandwich panels with superior high-power continuous wave laser resistance

Effect of highly-porous and lightweight carbon nanotube sponges on the high-power continuous wave laser ablation resistance of the sandwich panel was investigated experimentally. As a comparison, thermal responses of monolithic plate, carbon nanotube film filled sandwich panel, unfilled sandwich panel and carbon nanotube sponge filled sandwich panel subjected to continuous wave laser irradiation were analyzed. Experimental results showed that the laser resistance of the carbon nanotube filled sandwich panel is obviously higher than the unfilled structure. The added failure time of the sandwich panel by filling the cores with the carbon nanotube sponge of unit mass was about 18 times and 33 times longer than that by filling with the conventional ablative and insulated material. It could be understood by the high thermal diffusion coefficient and latent heat of sublimation of the carbon nanotube sponge. During ablation by the continuous wave, the carbon nanotube sponge not only fast consumed the absorbed laser energy through phase change of a large-area material due to its high latent heat of sublimation, but also quickly dispersed the heat energy introduced by the continuous wave laser due to its high thermal diffusion coefficient, leading to the extraordinary laser ablation resistance.

Damage characteristics of continuous-wave laser ablation triple-junction solar cells

The effect of laser irradiation on triple-junction GaAs cells studied via cell irradiation experiments was carried out using a continuous-wave laser with a wavelength of 808 nm. In the experiments, a thermal imaging system was used to measure the surface temperature of the cell, and the surface morphology of the irradiated cell was analyzed. The output performance of the irradiated cell was measured by a source meter, and the results show that the change rate of cell surface temperature increased with increasing laser power density. When the cell damage intensifies, the output characteristics of the cell gradually decay, and the cell loses its photoelectric effect.

Modeling the microwave transmittance of glass fiber-reinforced plastics subjected to laser ablation

The microwave transmittance of glass fiber-reinforced plastic (GFRP) slabs subjected to continuous-wave laser ablation was studied in the framework of continuum mechanics. First, a one-dimensional physical model involving laser absorption, heat conduction, resin pyrolysis, thermal radiation, and convection heat transfer was established to obtain the temperature field. An experiment-based absorption coefficient was proposed to capture the bulk-to-surface absorption transition during laser ablation. Second, the complex dielectric constant was modeled using a solid-state kinetic model describing the graphitization of pyrolysis products. The microwave reflectivity and transmittance were calculated based on the dielectric constant distribution. The agreement of the temperature and microwave transmittance with the experimental results suggests the feasibility of the model. The influence of laser power density, material thickness, and tangential airflow velocity on microwave transmittance was studied based on the model. The microwave transmittance changed nonmonotonically with increasing slab thickness owing to the competition between different physical mechanisms. The existence of tangential airflow reduced the decrease in microwave transmittance, particularly for weaker lasers. This study provides a useful physical model for predicting the microwave transmittance performance of GFRP in extreme heat environments.

Aluminum particle production on alumina rod surface by continuous-wave laser ablation

Continuous-wave laser ablation has been applied to alumina reduction with the eventual goal of lunar resource utilization. Aluminum particles were detected on the alumina rod surface after laser ablation. Impurity precipitation has been proposed as the aluminum particle production mechanism. For this study, distributions of aluminum particles and temperatures after laser ablation on an alumina rod surface were measured using SEM and two-color method. Laser power affected the aluminum particle distribution. The mean aluminum particle radius varied: 0.11–1.7 μm. The minimum value was consistent with the critical radius for aluminum nucleation in heterogeneous nucleation. The time history of surface temperatures was found to be independent of laser power. Therefore, aluminum particle production is expected to change with oxygen deficiency, and to increase with laser power. The obtained condition for aluminum particle production is applicable for an aluminum collection system in the alumina reduction method using laser ablation: the plate temperature of T = 933–2300 K and the cooling rate of 600–800 K/s.

Design and preparation of composite coatings with increased reflectivity under high-energy continuous wave laser ablation

High-energy continuous wave (CW) laser ablation can cause severe damage to structural materials in an extremely short time, which generates considerable concern in terms of material safety. For the purpose of reducing or even eliminating such laser-induced damage, a novel composite coating consisting of a boron-modified phenolic formaldehyde resin incorporating ZrC and SiC has been designed and prepared. The experimental results reveal that ZrC and SiC are rapidly oxidized to ZrO2 and SiO2 respectively, leading to the formation of a white ceramic layer consisting of ZrO2 particles and melted SiO2. After ablation at 1000 W/cm2 for 50 s, elemental analysis indicates that no Si can be found in the central ablation zone because of gasification. A relatively compact ZrO2 layer is formed through the sintering of adjacent ZrO2 particles, which effectively improves the reflectivity of the coating from 7.3% (before ablation) to 63.5% (after ablation). The high reflectivity greatly reduces the absorption of laser energy. In addition, no obvious ablation defects are observed in the composite coating. The excellent anti-laser ablation performance of the coating makes it a promising system for protecting a material against the effects of long-term CW laser ablation.

Experimental investigation on laser ablation of C/SiC composites subjected to supersonic airflow

Continuous wave laser ablation behavior of C/SiC composites subjected to supersonic airflow, as well as in static air environment, is investigated experimentally. Ablation morphology and microstructure of the ablation region are measured by 3D digital microscope system and profiling system, respectively. Effects of supersonic airflow on the ablation morphology and ablation rates of the C/SiC composite are analyzed. Experimental results indicate that the mechanical erosion by supersonic airflow increases the ablation rates and smoothens the ablation surface. Many carbon fibers are left at the edge of center region due to the cooling effect of the supersonic airflow. The laser ablation behavior of C/SiC composites in supersonic airflow is attributed to the combined effect of convective cooling and mechanical erosion.

Influence of gold nanolayer coating on the continuous-wave laser ablation of a pure aluminum surface: Evaluations of structural and optical features

In this paper, formation of uniform and large-area micro/nanostructures on pure aluminum surfaces using a continuous-wave laser irradiation is presented. Gold nanolayer coating was utilized as a confinement layer for controlling the possible hydrodynamic phenomena in a molten area. Dependency of the laser-induced morphology on the thickness of a gold coating was investigated in this regard. Scanning electron microscopy, energy dispersive spectroscopy, grazing test of the X-ray diffraction, and optical absorption/reflection spectroscopy in UV/visible/IR ranges were employed to characterize the samples. Results showed that the formation of uniform structures of average sizes of 50 nm-5 μm on aluminum surface was possible following the irradiation of a continuous-wave CO2 laser, delivering 130 W beam power. Alterations of the surface morphology brought about an increase in specific absorption peaks at the UV region and the appearance of an absorption peak in the visible range. In addition, these structure-covered surfaces provided interesting reflection behaviors in different spectral areas, which can clearly reflect their high potential to be used as selective solar absorbers. The results of this investigation indicated that optical characteristics such as absorption and emission coefficients as well as ξ factor were 0.98, 0.13, and 7.53, respectively. It can therefore be concluded that this process can be considered an efficient and fast technique to fabricate selective solar absorbers.

Silicon-catalyzed growth of amorphous SiO x nanowires by continuous-wave laser ablation of SiO in high-pressure gas

Continuous-wave laser ablation of an SiO target was performed to grow nanowires (NWs) in high-pressure (up to 0.90 MPa) Ar, N2, and O2 gas. In Ar gas, the fraction of the NWs in deposits was changed significantly by the Ar pressure. As Ar pressure increased, thicker NWs with diameters of up to 80 nm were grown. The NWs were amorphous SiO x and attached with sphere-like nanoparticles (NPs) at their tips. The tip NPs were composed of crystalline Si covered with thin amorphous SiO x layers. Similar NW growth occured in N2 gas. However, only amorphous NPs were generated in O2 gas. On the basis of liquid-like molten SiO x NPs containing a portion of a Si phase formed by a disproportionation reaction of SiO x , we discuss the nucleation and growth of the NWs through supersaturation and anisotropic precipitation of SiO x .

Cavitation-Free Continuous-Wave Laser Ablation from a Solid Target to Synthesize Low-Size-Dispersed Gold Nanoparticles.

Continuous wave (CW) radiation from a Yb-fiber laser (central wavelength 1064 nm, power 1-200 W) was used to initiate ablation of a gold target in deionized water and to synthesize bare (unprotected) gold nanoparticles. We show that the formed nanoparticles present a single low-size-dispersed population with a mean size of the order of 10 nm, which contrasts with previously reported data on dual populations of nanoparticles formed during pulsed laser ablation in liquids. The lack of a second population of nanoparticles is explained by the absence of cavitation-related mechanism of material ablation, which typically takes place under pulsed laser action on a solid target in liquid ambience, and this supposition is confirmed by plume visualization tests. We also observe a gradual growth of mean nanoparticle size from 8-10 nm to 20-25 nm under the increase of laser power for 532 nm pumping wavelength, whereas for 1064 nm pumping wavelength the mean size 8-10 nm is independent of radiation power. The growth of the nanoparticles observed for 532 nm wavelength is attributed to the enhanced target melting and splashing followed by additional heating due to an efficient excitation of plasmons over gold nanoparticles. Bare, low-size-dispersed gold nanoparticles are of importance for a variety of applications, including biomedicine, catalysis, and photovoltaics. The use of CW radiation for nanomaterial production promises to improve the cost efficiency of this technology.

Reliable and well-controlled synthesis of noble metal nanoparticles by continuous wave laser ablation in different liquids for deposition of thin films with variable optical properties

We report the results of continuous wave laser interactions with both gold and silver targets in the presence of different liquids (deionized water, ethanol, and glycerol). Upon moderate laser irradiation at wavelength of 1.06 nm during 30 min, nanoparticle colloids are shown to be formed with surprisingly narrow size distributions and average dispersion as small as 15–20 nm. The average particle sizes range between 8 and 52 nm for gold and between 20 and 107 nm for silver. This parameter is shown to be stable and well-controlled by such laser parameters as intensity and effective irradiation time, as well as by the choice of the liquid phase. The possibilities of an efficient control over the proposed synthesis techniques are discussed, and the results of a bimetallic Au–Ag structure deposition from the obtained colloids are presented. The formation of the extended arrays of gold and silver nanoparticles with controlled morphology is examined. The changes in the optical properties of the obtained thin films are found to depend on their morphology, in particular, on the particle size, and distance between them.

Experimental investigation and numerical simulation on continuous wave laser ablation of multilayer carbon fiber composite

Laser beam machining is one of the most widely used advanced processing techniques, which can be applied to compound materials. As a large number of photons are absorbed into the composite, the subsequent local heat storage, charring and potential delamination make the study for the effect of laser on complex materials become significant. In this paper, a carbon fiber epoxy composite laminated sheet is irradiated by continuous wave chemical oxygen iodine laser. The peak temperature of front surface, the temperature distribution of rear surface, and the appearance of ablation zone are presented. Further, based on the birth–death elements technique of finite element method, a three-dimensional model for simulating the transient temperature distribution and material removal has been developed under the same condition. The results reveal that the peak temperature of irradiated region ranges from 2800 K to 3100 K, and the center point shows a higher temperature rise rate than the surroundings in the irradiated zone. The measured data and predicted data are in a good consistency, which suggests that the numerical model is appropriate for simulating laser ablation of carbon fiber epoxy composites.

Antibacterial effects of laser ablated Ni nanoparticles

The interaction of nickel nanoparticles with Escherichia coli (E. coli) bacteria has been studied. The nickel nanoparticles have been fabricated by continuous wave laser ablation of nickel target and their properties are studied using different characterization techniques. The antibacterial activity of nickel nanoparticles was checked against E. coli bacteria. Escherichia coli were cultured in nutrients broth and different concentrations of nickel nanoparticles were added to bacterial culture solution to investigate the interaction of nickel nanoparticles with bacteria and to check toxicity of the nickel nanoparticles against E. coli. The fabricated Ni nanoparticles have exhibited considerable antimicrobial activity against E. coli.

Catalyst-free growth of amorphous silicon nanowires by laser ablation

Amorphous silicon nanowires (NWs), 3–50 nm thick and up to 4 μm long, were grown by room-temperature continuous wave laser ablation of Si in high-pressure (0.1–0.9 MPa) Ar gas without the addition of any catalysts. The diameter and length of the NWs increased as the pressures of the ambient Ar increased. Sphere-like Si particles with diameters of 4–110 nm were observed at the tips of grown NWs and their diameters exhibited a strong correlation with the NW diameters. We propose a stress-driven self-catalytic vapor-liquid-solid mechanism to explain the growth of the NWs.

Characteristics of γ-Al2O3 nanoparticles generated by continuous-wave laser ablation in liquid

Laser ablation in liquid is one of the most widely investigated methods for generating various nanoparticles (NPs) that are difficult to produce using other means. In this paper, we report the generation of Al-oxide NPs by continuous-wave (CW) fibre laser ablation of corundum (α-Al2O3) target submerged in deionised water. The effects of CW fibre laser power and radiation time have been investigated. Characterisation of the NPs generated, in terms of size, size distribution, shape, chemical composition, and phase structure, was carried out by means of high-resolution transmission electron microscopy (HR-TEM), high angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the average size of Al-oxide NPs, in the range of 17 to 29 nm, increased with increasing the laser power and laser exposure time, and the NPs are dominated by stoichiometric γ-Al2O3 with a minor phase of α-Al2O3. The mechanism involved in the CWLAL is also discussed.

The effect of laser power on the formation of carbon nanotubes prepared in CO 2 continuous wave laser ablation at room temperature

Single-walled carbon nanotubes (SWNTs) were prepared by continuous wave CO 2 laser ablation without applying additional heat to the target. Transmission electron microscope and Raman spectrum were used to investigate the effect of laser power on the growth and diameter distribution of the tubes. The average diameter of single wall carbon nanotubes produced by CO 2 laser increases with increasing laser power. We have presented the radial breathing mode of Raman spectrum of SWNTs prepared by using CO 2 continuous laser vaporization in laser power from 500 to 850 W, and the Raman spectrum are also compared with those of single-walled carbon nanotubes produced by pulsed CO 2 laser ablation of previous reports. SWNTs and bamboo-shaped carbon nanotubes were observed from web-like carbon soot in a lower laser power of 500 W. Experiment confirmed that laser power play a crucial role in SWNTs formation and diameter distribution.

Continuous wave laser ablation of tissue: analysis of thermal and mechanical events.

Thermal and mechanical events during continuous wave (CW) laser ablation of biological and phantom media were investigated. Porcine aortae, collagen fibers, and polyacrylamide control samples were subjected to argon laser irradiation while infrared and high-speed (240 images/s) video cameras were used to monitor their surfaces. Subsequent analysis of simultaneous changes in surface temperature and physical features correlated thermal and mechanical events. Video images recorded prior to ablation onset of tissue slabs clearly revealed two distinct phases: 1) progressive growth of a surface dehydration zone, and 2) surface deformation, implying subsurface bubble formation. Surface temperature recordings and video imaging revealed that the onset of CW ablation of soft biological media often initiated with a violent explosion, surface tearing, and tissue ejection. Histological inspection revealed intense coagulation in superficial layers near the irradiation site, whereas chiefly mechanical disruption was noted at the base of the crater. Ablation characteristics were consistent with theoretical calculations which indicate subsurface temperature peaks that increase in magnitude and surface proximity as energy deposition rates are increased. Results also suggested that mechanical properties of target media strongly influenced the extent of pressure built up, the nature of ablation onset, and the characteristics of the overall ablation pathway.

The paradox of thermal ablation without thermal injury

Previous investigations have demonstrated in vitro that the excimer laser may be used to accomplish cardiovascular tissue ablation without causing thermal injury to boundary sites. Initial investigations suggested that results achieved with the excimer laser were related to photochemical breaking of molecular bonds, rather than thermal degradation. More recent investigations, however, have suggested that the mechanism of excimer tissue ablation may not be unique. Results indistiguishable from those accomplished with the excimer laser have been reproduced using both visible and infrared wavelengths. Experiments utilizing gas chromatography have indicated that the vapour-phase photoproducts liberated during excimer laser tissue ablation are indistinguishable from those observed following continuous wave laser irradiation or flame torching of cardiovascular tissue. While photoemission spectroscopic analysis has identified free radicals released in gas phase during excimer laser ablation, electron paramagnetic resonance spectroscopy has similarly identified free radicals released in solution during continuous wave laser ablation; while these two techniques may detect different types of radicals with different kinetic behaviour, these results indicate, that the finding of free radical photoproducts per se during laser ablation does not necessarily exclude a non-thermal mechanism. Finally, plasma-mediated photodisruption represents a third alternative to explain pulsed laser ablation; experiments are required, however, to define whether plasma generated during pulsed laser irradiation is central to the ablation process, or represents an epiphenomenon.