Ablation Process Research Articles

Comparison of material removal efficiency in laser ablation of polycrystalline diamond for different pulse durations

The study experimentally investigates the effect of three different pulse durations on the laser ablation of polycrystalline diamond (PCD), focusing on ablation depth and the morphology of the ablated craters. The results indicate that as the number of incident pulses (N.P) increases, the ablation depth per pulse reaches a constant value. A considerable difference in ablation depth, by nearly a factor of two, was observed for the 16 ns pulses compared to 12 ps and 250 fs pulses. In addition to the single-point experiment, three volume ablation tests with these pulse durations were performed. The results show that the material removal rates for the ns, fs, and ps lasers are the highest, respectively. Additionally, the ablation efficiency in volume ablation process was compared with single-point process, indicating considerable inconsistency in removal depth for ns and ps lasers.

Non-steady flow decomposition behaviors of heat and mass transfer on intrinsic kinetics for methane hydrate particles transported in pipelines

The differential equations governing the decomposition rate and activation energy, convective mass transfer, methane diffusion and fugacity, as well as heat conduction and enthalpy change were derived by integrating thermal convection, heat conduction, mass transfer and intrinsic kinetics. Mathematical models for decomposition kinetics and thermodynamics in a non-steady field were solved using a radial logarithmic grid for node division and discretization of the equations. The study elucidated the heat and mass transfer processes as well as decomposition kinetics in pipelines by analyzing the impacts of particle size, temperature, pressure, flow rate and activation energy on decomposition rate. The results indicated that compared with the isothermal decomposition of the intrinsic kinetic model and static experimental decomposition, the complex non-steady multiphase flow model offers a more accurately simulation of hydrate decomposition as well as associated heat and mass transfer processes. Hydrate decomposition is characterized as a non-isothermal dynamic ablation process with heat transfer rate and intrinsic kinetics dominating during the preliminary stage and the stable stage, respectively. An increasing in the slurry temperature, temperature fluctuation and flow rate accelerated the heat transfer rate capacity, enhanced convective heat transfer capacity and facilitated hydrate decomposition, with the mass transfer rate exhibiting lesser influence. The particle surface area and slurry temperature exhibited the most significant influence on hydrate decomposition, which was followed by flow rate. Upon increasing particle size from 1 mm to 5 mm and the temperature from 293 K to 313 K, the decomposition rate increased by 20.7 times and 13.5 times, respectively. Furthermore, enhancing temperature and flow rate while decreasing particle size and pressure decreased both the decomposition time and the duration required for the decomposition rate to reach its peak. Additionally, the decomposition rate and its constant vary with the activation energy.

Ablation and molten layer flow simulation for plate model of SiO2f/SiO2 composite material using particle method

In this paper, the moving particle semi-implicit method (MPS) is extended from calculating free mobility to simulating the extremely viscous and temperature-dependent molten layer flow of SiO2f/SiO2 composite material under aerodynamic heating conditions, which includes strong heating and shear of incoming flow. A method for applying heat flux and airflow shear, based on the conceptual particle approach, has been established. Heat transfer, melting, solidification, and evaporation behaviors are considered, with temperature-dependent viscosity variations also accounted for. The ablative regression of the plate model is verified using experimental results of the SiO2f/SiO2 composite material, and results from convergence analysis demonstrate the accuracy of the space step size selection. Surface morphology analysis through three-dimensional computation indicates that the extended particle method also accurately describes the surface morphology of SiO2f/SiO2 composite material under aerodynamic heating conditions. Thus, the extended particle method accurately simulates both the ablation process and the surface morphology of the SiO2f/SiO2 composite material. The influences of acceleration and surface tension are discussed. Ablative recession, when subject to acceleration, is smaller than that observed in its absence. When exposed to surface tension, the liquid layer tends to form a spherical shape, and the particles behave as a cohesive unit, resulting in smaller ablative recession than in the absence of surface tension.

Ablation resistance of C/C–Hf1-xZrxC composites under an oxyacetylene flame at above 2700 °C

To the better application of C/C composites in thermal components of vehicles above 2700 °C, C/C–Hf1-xZrxC composites were prepared by CLVD, and the ablation behavior of composites was investigated. The results show that C/C–Hf0.5Zr0.5C has excellent ablation properties with linear and mass ablation rates of −0.23 μm/s and −0.31 mg/(s·cm2), respectively. ZrO2 molten phase and HfxZr1-xO2 particles are generated on the surface of C/C–Hf1-xZrxC composites during ablation. During the ablation process, defects are healed by the ZrO2 molten phase due to its mobility, which inhibits the diffusion of oxygen into the substrate. The ZrO2 molten phase is stabilized by the pinning effect of the HfxZr1-xO2 particles, which makes the ZrO2 molten phase better resistant to the scouring of the air stream. A relatively complete oxide layer is generated on the C/C–Hf0.5Zr0.5C surface, with a moderate amount of HfxZr1-xO2 exerting a pinning effect to hold the ZrO2 molten phase.

Seasonal snow–atmosphere modeling: let's do it

Abstract. Mountain snowpack forecasting relies on accurate mass and energy input information in relation to the snowpack. For this reason, coupled snow–atmosphere models, which downscale input fields to the snow model using atmospheric physics, have been developed. These coupled models are often limited in the spatial and temporal extents of their use by computational constraints. In addressing this challenge, we introduce HICARsnow, an intermediate-complexity coupled snow–atmosphere model. HICARsnow couples two physics-based models of intermediate complexity to enable basin-scale snow and atmospheric modeling at seasonal timescales. To showcase the efficacy and capability of HICARsnow, we present results from its application to a high-elevation basin in the Swiss Alps. The simulated snow depth is compared throughout the snow season to aerial lidar data. The model shows reasonable agreement with observations from peak accumulation through late-season melt-out, representing areas of high snow accumulation due to redistribution processes, as well as melt patterns caused by interactions between radiation and topography. HICARsnow is also found to resolve preferential deposition, with model outputs suggesting that parameterizations of the process using surface wind fields may only be inappropriate under certain atmospheric conditions. The two-way coupled model also improves surface air temperatures over late-season snow, demonstrating added value for the atmospheric model as well. Differences between observations and model outputs during the accumulation season indicate a poor representation of redistribution processes away from exposed ridges and steep terrain and a low bias in albedo at high elevations during the ablation season. Overall, HICARsnow shows great promise for applications in operational snow forecasting and in studying the representation of snow accumulation and ablation processes.

Ultrasonic vibration-assisted femtosecond laser submerged ablation process for the preparation of titanium-based crack-free hydroxyapatite

Titanium alloy-based hydroxyapatite (HAp) coating materials are beneficial for reducing stress shielding and improving the biocompatibility of implants. However, the significant disparity in thermal conductivity between titanium alloy and hydroxyapatite results in the material being highly susceptible to cracking during preparation, which diminishes the mechanical properties of the material and predisposes the implant to aseptic loosening. To obtain coatings of HAp that are free of cracks, this study proposes a process method of ultrasonic-assisted femtosecond laser under-liquid ablation of a Ca/P solution to synthesize HAp by a one-step process and apply coatings on the surface of TC4 titanium alloy. The relationship between the laser process parameters and the resulting surface morphology, coating spatial distribution, elemental composition, chemical state of the elements, phase, coating thickness, coating bonding, friction coefficient, corrosion resistance and the number of cells was investigated through a series of analytical techniques, including high-speed photographic observation, scanning electron microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), scratch testing, Tafel plot and cell adhesion assays. The findings demonstrate that titanium-based HAp coatings with a thickness of 42.5 μm, a bonding force of 55 N, a polarization resistance of 10 Ω.cm2, the absence of cracks defects, and notable bioactivity can be produced with ultrasonic-assisted submerged laser ablation in a highly concentrated Ca/P solution. The proposed method represents a novel approach to the preparation of multifunctionalized implants.

Ceramic Matrix Composite Cyclic Ablation Behavior under Oxyacetylene Torch.

To study the ablation properties and differences of plain-woven SiC/SiC composites under single and cyclic ablation. The ablation test of plain-woven SiC/SiC composites was conducted under an oxyacetylene torch. The results indicate that the mass ablation rate of cyclic ablation is lower than that of single ablation, whereas the line ablation rate is higher. Macro-microstructural characterization revealed the presence of white oxide formed by silica on the surface of the ablation center region. The fibers in the central region of the ablation were ablated layer by layer, and the broken fiber bundles exhibited a spiky morphology with numerous silica particles attached. The oxide layer on the surface and the silica particles on the fibers, which are in the molten state formed in the high-temperature ablation environment, contribute to resisting ablation. Thermal shock during cyclic ablation also played a role in the ablation process. The thermal shock causes cracks in the fiber bundles and matrix of the SiC/SiC composites. This study helps to apply SiC/SiC composite to complex thermal shock environments.

Ablation behaviour and mechanism of in-situ NbC composite coating under plasma jet

NbC composite coatings of Nb2O5-Al-SiC system (in-situ) and NbC-SiC-Al2O3 system (ex-situ) were successfully prepared on graphite substrate by plasma spraying, respectively. The ablation resistance of two systems of NbC composite coatings was evaluated by plasma jet, and the ablation mechanism of the Nb2O5-Al-SiC system coating prepared in-situ was revealed. The results showed that the NbC-SiC-Al2O3 system composite coating has completely failed after ablation for 10 s, and the Nb2O5-Al-SiC system coating only has a small amount of spalling at the edge of the coating surface after ablation for 20 s. The excellent ablation resistance of Nb2O5-Al-SiC system coating was attributed to the formation of a Nb2O5 liquid-phase film on the surface of the coating during the ablation process, which can effectively block the penetration of heat and oxygen into the coating. Moreover, the reaction between Nb2O5 and Al2O3 at high temperatures generated the high-temperature stable phase AlNbO4, which can further improve the structural stability of the Nb2O5 film, and then improve the ablation resistance of the Nb2O5-Al-SiC system coatings.

High efficiency femtosecond laser ablation of alumina ceramics under the filament induced plasma shock wave

Femtosecond laser filament enables energy transfer over long distances, which is of great value for studying long-range ablation. However, the energy coupling of filament with the plasma generated by the ablation process leads to a very complex behavior which limits the ablation efficiency. This study systematically investigated the ablation mechanism of laser-induced filament in alumina ceramic. The plasma shock wave was initially investigated using spectral detection techniques combined with Sedov-Taylor theory. The results indicated that the maximum plasma shock wave reached 30 MPa under the irradiated by a 1 mJ fs laser. The theoretical analysis confirmed the effectiveness of the filament-induced plasma shock wave in enhancing the ablation rate of alumina ceramic. In this context, the experimental studies were conducted with varying filament positions and pulse energies, and the corresponding ablation rates for each parameter were investigated. The filament in the ablation process was found to has a secondary sputtering effect, which is an effective contributor to enhance the ablation rate. The corresponding ablation depth reach to 550 μm while achieving an ablation rate of 3.1 μm3/μJ. Finally, the coupling mechanism between the femtosecond laser filament and the plasma shock wave was systematically revealed. This research will facilitate future laser remote ablation applications with high efficiency.

A cell membrane-targeted photosensitizer for cancer photodynamic therapy and dynamic ablation process tracking

Photodynamic therapy (PDT) uses photosensitizer (PS) to generate reactive oxygen species (ROS) under light to trigger cell apoptosis in cancer treatment. Organelle-targeted PS can effectively enhance the efficacy of phototherapy by specifically destroying subcellular organelles. The cell membrane, as an important organelle, is the “protective wall” of cells maintaining the integrity and normal life activities of cells. The damage to cell membranes is fatal to cells. However, utilizing functional PS to achieve cell membrane-targeted PDT, and realize real-time and accurate in situ reporting of cell membrane damage and monitoring of the treatment process, are challenging tasks. In this work, we prepared a photosensitizer (2TPAO) with aggregation-induced emission (AIE) characteristics, good water solubility, strong near-infrared fluorescence, and the capability for specific imaging of cell membranes. Moreover, 2TPAO could effectively produce ROS under visible light irradiation and achieve photodynamic ablation of tumor cells and tumors. Meanwhile, during PDT, the fluorescence changes of 2TPAO indicated the destruction of cell membranes, allowing intuitive determination of the phototherapy results. Therefore, 2TPAO is an effective cell membrane-targeted PS for cancer PDT.

A deterministic mechanism for efficient removal of arsenic and lead from wastewater using rapidly synthesized TiO2-(α-Fe2O3) nanoshells

Removal of heavy metals from wastewater using efficient techniques became demanding wherein various nanomaterials with tailored physicochemical traits can be useful. Thus, PLAL approach at an optimum laser energy was used to make TiO2-(α-Fe2O3) nanoshells (TFNSs) by mixing nanoparticles (NPs) suspension of TiO2NPs (TNPs) and α-Fe2O3NPs (FNPs) at 50 to 50 ratio. The produced nanocomposites were customized by targeting Ti that was submerged in deionized water as growth medium and then irradiate using the laser pulses with an optimum laser energy 10.6 J/cm2, spot focused size of 1.2 ± 0.2 mm, frequency of 6 Hz, and laser beam with a pulse duration of 8 ns for 15 minutes. In the course of the ablation process, the solution was agitated to achieve the formation of TNPs, FNPs, and TFNSs by preventing the formation of craters on the target surface. The obtained NSs were characterized to evaluate their structural, morphological, optical absorption and fluorescence characteristics. TEM micrographs of the liquid suspension confirmed the existence of spherical nanocrystallites of TiO2-(α-Fe2O3)NSs with mean diameter ≈12.4 ± 1.31 nm. XRD and FTIR results have been used to identify the samples crystalline nature and high purity. LSPR absorption bands of TFNSs were evidenced at 230 to 300 nm. These NSs showed prominent fluorescence peaks escorted with blue shift. Arsenic and lead removal efficiency of TFNSs from wastewater was better (over 99% at pH = 9) than TNPs and FNPs. The removal of arsenic and lead from wastewater by TNPs, FNPs and TFNSs were explained using a possible mechanism. The obtained results suggest that the proposed NSs can be potential for wastewater treatment, contributing towards sustainable growth.

ULPING-Based Titanium Oxide as a New Cathode Material for Zn-Ion Batteries

The need for alternative energy storage options beyond lithium-ion batteries is critical due to their high costs, resource scarcity, and environmental concerns. Zinc-ion batteries offer a promising solution, given zinc’s abundance, cost effectiveness, and safety, particularly its compatibility with non-flammable aqueous electrolytes. In this study, the potential of laser-ablation-based titanium oxide as a novel cathode material for zinc-ion batteries was investigated. The ultra-short laser pulses for in situ nanostructure generation (ULPING) technique was employed to generate nanostructured titanium oxide. This laser ablation process produced highly porous nanostructures, enhancing the electrochemical performance of the electrodes. Zinc and titanium oxide samples were evaluated using two-electrode and three-electrode setups, with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge (GCD) techniques. Optimal cathode materials were identified in the Ti-5W (laser ablated twice) and Ti-10W (laser ablated ten times) samples, which demonstrated excellent charge capacity and energy density. The Ti-10W sample exhibited superior long-term performance due to its highly porous nanostructures, improving ion diffusion and electron transport. The potential of laser-ablated titanium oxide as a high-performance cathode material for zinc-ion batteries was highlighted, emphasizing the importance of further research to optimize laser parameters and enhance the stability and scalability of these electrodes.

Improved oxidation and ablation resistance of SiCf/SiC-HfB2 composites: Role of oxygen-blocking scale and protection mechanism

To improve the oxidation and ablation resistance of SiCf/SiC composites, the as-synthesized ultrafine HfB2 powder was used as the modification phase to fabricate SiCf/SiC-HfB2 composites, and their oxidation and ablation behaviors were investigated. Compared with the unmodified SiCf/SiC composites, the oxidation resistance at 800–1500 °C and the ultra-high temperature ablation resistance of SiCf/SiC-HfB2 composites were significantly improved. After oxidation, a compact compound glass scale consisting of HfO2, HfSiO4 and Si-Hf-O glass was formed, providing the effective oxidation protection. A dual-phase oxide scale composed of HfO2 skeleton and Si-Hf-O glass was formed after ablation, exhibiting the high viscosity, the significant oxygen-blocking effect and resistance to gas flow scouring. The improved oxidation and ablation resistance of SiCf/SiC-HfB2 composites could be attributed to the effective protective role of oxygen-blocking scales formed during the oxidation and ablation processes.

Iron nanoparticles supported on graphene nanosheets by pulsed laser ablation method in deionized water

In this study, pulsed laser ablation process (PLA) in deionized water solution was used to prepare graphene oxide (GO) nanosheets, wustite (FeO) nanoparticles and GO based FeO nanoparticles. The effect of composition ratio of materials on their optical properties was studied. The structural properties of the materials were characterized using transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques. According to the TEM results, FeO nanoparticles were well deposited on GO nanosheets. The XRD results demonstrated the formation of Fe and wustite (FeO) phase of iron oxide nanoparticles. In the XRD analysis of graphene sample, graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets were identified. The absorption measurement of the samples in colloidal state was performed using a UV–vis single beam spectrophotometer in the wavelength range of 250 to 800 nm. The higher and the lower absorbance belonged to 1.4 ml GO − 0.6 ml FeO composition and GO nanosheets, respectively. The linear optical properties of the samples, including the real and imaginary parts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were calculated using the spectroscopic ellipsometry (SE) method. Leng oscillator was used as the optical model in SE method. Also, the energy band gap of the samples was calculated using Tauc relation, in which the lower and the higher energy band gaps were obtained for GO nanosheets (3.40 eV) and FeO nanoparticles (4.65 eV), respectively. Furthermore, the nonlinear optical properties of GO based FeO nanoparticles were investigated by Z-scan measurement. The nonlinear refractive index and nonlinear absorption coefficient were obtained in the order of 10−8 cm2 W−1 and 10–4 cm W−1, respectively.

Investigations of the Laser Ablation Mechanism of PMMA Microchannels Using Single-Pass and Multi-Pass Laser Scans.

CO2 laser machining is a cost effective and time saving solution for fabricating microchannels on polymethylmethacrylate (PMMA). Due to the lack of research on the incubation effect and ablation behavior of PMMA under high-power laser irradiation, predictions of the microchannel profile are limited. In this study, the ablation process and mechanism of a continuous CO2 laser machining process on microchannel production in PMMA in single-pass and multi-pass laser scan modes are investigated. It is found that a higher laser energy density of a single pass causes a lower ablation threshold. The ablated surface can be divided into three regions: the ablation zone, the incubation zone, and the virgin zone. The PMMA ablation process is mainly attributed to the thermal decomposition reactions and the splashing of molten polymer. The depth, width, aspect ratio, volume ablation rate, and mass ablation rate of the channel increase as the laser scanning speed decreases and the number of laser scans increases. The differences in ablation results obtained under the same total laser energy density using different scan modes are attributed to the incubation effect, which is caused by the thermal deposition of laser energy in the polymer. Finally, an optimized simulation model that is used to solve the problem of a channel width greater than spot diameter is proposed. The error percentage between the experimental and simulation results varies from 0.44% to 5.9%.

Damage mechanism and bending properties degradation of aviation composite honeycomb sandwich structures under laser irradiation

Damage mechanism and bending properties degradation of aviation composite honeycomb sandwich structures are studied under different laser conditions in this paper. Firstly, the damage test of composite honeycomb sandwich structures is conducted. Temperature field and ablation process during laser irradiation are analyzed. Damage morphology and mechanism are verified. Secondly, the influence of laser damage on the bending properties of composite honeycomb panels is studied. Progressive damage process and failure mechanism of honeycomb structures during loading are explored by digital image correlation (DIC) and strain trend. The results show that the temperature at the center point of front surface reaches more than 2000 °C within 1 s under the laser irradiation, while the temperature of back surface exhibits hysteresis. The ablation hole is funnel-shaped and has severe delamination. In the heat affected zone (HAZ), resin matrix has been basically sublimated and oxidized, leaving only carbon fiber bundles and some residual carbon. The honeycomb core in this area has been completely carbonized and deformed. During bending process, the honeycomb core breaks firstly, and strain appears peak at both crack ends, leading the crack extend along both sides. The ultimate load of damaged specimen is 2.35kN, which has a 42.26 % drop compared to that of healthy specimen 4.07kN. Bending properties of specimen are significantly degraded by laser damage.

Analysis of the periodic variation of pellet ablation radiation intensity in ASDEX Upgrade

Abstract In a future fusion reactor, the main fuelling method will likely rely on the injection of solid hydrogen pellets. Current predictions assume that this goal can be achieved, since being based on a technology which is already largely developed. However, this belief is founded on modelling tools that are usually aligned to the observation made in existing devices and then extrapolated to reactor conditions. This approach needs a sound consideration of its intrinsic restrictions and any observed feature not reproduced by the utilised codes should be applied to check their validation and possibly contribute to their refinement. One specific feature still lacking an explanation of a reasonable and self-consistent mechanism in the current models is the appearance of a phenomenon called striations, which are high frequency variations in the radiation emitted during the pellet ablation process. In order to provide a sound and reliable database for further considerations, a dedicated analysis of this effect has been performed on the mid-size tokamak ASDEX Upgrade. Therefore, such cases have been selected with the relevant signal recorded with sufficient temporal resolution during experiments covering a wide variation of plasma and pellet parameters which are regarded to be potentially influential on the striation pattern. In addition, it was ensured that for any specific case the observed behaviour was reproducible for several individual ablation events under identical conditions. In all cases considered, the observed radiation-intensity variations appear with a typical pattern showing a broad peak of frequencies in the range 50 to 150 kHz. This characteristic unveils a notable resilience against any parameter variation. This new collection of data can now act as firm basis to corroborate future modelling code-validation efforts. In addition, the analysis method can provide a relatively simple way of reviewing future modelling predictions.

Intraoperative Ablation Control Based on Real-Time Necrosis Monitoring Feedback: Numerical Evaluation.

Ablation therapy is a type of minimally invasive treatment, utilized for various organs including the brain, heart, and kidneys. The accuracy of the ablation process is critically important to avoid both insufficient and excessive ablation, which may result in compromised efficacy or complications. The thermal ablation is formulated by two theoretical models: the heat transfer (HT) and necrosis formation (NF) models. In modern medical practices, feed-forward (FF) and temperature feedback (TFB) controls are primarily used as ablation control methodologies. FF involves pre-therapy procedure planning based on previous experiences and theoretical knowledge without monitoring the intraoperative tissue response, hence, it can't compensate for discrepancies in the assumed HT or NF models. These discrepancies can arise due to individual patient's tissue characteristic differences and specific environmental conditions. Conversely, TFB control is based on the intraoperative temperature profile. It estimates the resulting heat damage based on the monitored temperature distribution and assumed NF model. Therefore, TFB can make necessary adjustments even if there is an error in the assumed HT model. TFB is thus seen as a more robust control method against modeling errors in the HT model. Still, TFB is limited as it assumes a fixed NF model, irrespective of the patient or the ablation technique used. An ideal solution to these limitations would be to actively monitor heat damage to the tissue during the operation and utilize this data to control ablation. This strategy is defined as necrosis feedback (NFB) in this study. Such real-time necrosis monitoring modalities making NFB possible are emerging, however, there is an absence of a generalized study that discusses the integration and quantifies the significance of the real-time necrosis monitor techniques for ablation therapy. Such an investigation is expected to clarify the universal principles of how these techniques would improve ablation therapy. In this study, we examine the potential of NFB in suppressing errors associated with the NF model as NFB is theoretically capable of monitoring and suppressing the errors associated with the NF models in its closed control loop. We simulate and compare the performances of TFB and NFB with artificially generated modeling errors using the finite element method (FEM). The results show that NFB provides more accurate ablation control than TFB when NF-oriented errors are applied, indicating NFB's potential to improve the ablation control accuracy and highlighting the value of the ongoing research to make real-time necrosis monitoring a clinically viable option.

Effects of laser ablation of olivine on chamber optical window transmission loss and its recovery

Optical windows play a crucial role in laser ablation systems by protecting delicate components inside the chamber while allowing the transmission of laser energy. However, material buildup during the laser ablation process can lead to a significant loss of optical transmission over time. In this work, material deposition on the optical window by laser ablation of olivine using two laser systems operating at 30 kHz, 1 mJ pulse energy, and 20 Hz, 9.6 mJ pulse energy was performed and its impact on the window’s transmission properties, laser-induced breakdown spectroscopy (LIBS) signal, and window recovery is presented. Ablation at 30 kHz with 1 mJ pulses for 10 min resulted in substantial particle deposition on the window, causing a significant drop in transmission. Transmission of clean window dropped abruptly from 90% to nearly 0% (in the UV region from 200 to 300 nm) and 35% (at 600 nm) affecting the LIBS signal. In contrast, ablation at 20 Hz with 9.6 mJ pulses for 5 min showed no material deposition or transmission loss. Additionally, the study demonstrated that the same laser system used for ablation could be employed to remove the deposited material from the window, facilitating its recovery. Laser cleaning of the window at 30 kHz and 12 W average power restored the transmission values from 39% to 62% at 400 nm in the UV region, with potential for further improvement through parameter optimization. In addition, the identification of the hydroxyl group in olivine, which is relevant to NASA’s terahertz heterodyne spectrometer for in situ resource utilization project for the validation of water molecules is presented.

A finite volume formulation for one-dimensional Stefan problems

This paper presents a numerical formulation that combines the finite-volume method with a time-dependent boundary-fitted coordinate system to tackle the moving boundary problems for the one-dimensional (1-D) heat equation. Following the formulation process, an algorithm was created with the help of the linear algebra package Eigen to generate the data for the numerical solution. Four benchmark cases of heat conduction were investigated by this approach and compared to the analytical solution: a fixed boundary case, the liquid phase of a melting process, the solid phase of a melting process, and an ablating process. The results demonstrate the capability of the presented numerical formulation in efficiently solving the general 1-D heat problems, especially the one-phase Stefan problems, as well as the consistency of the numerical and analytical solutions. Future works can strive to extend the formulations to Stefan problems of two phases or higher dimensions. The work can then be extended to real-life applications, such as the spacecraft re-entry ablation process, and the process of iceberg melting, demonstrating its critical value in solving practical problems.