• Advances in Computational Design
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• v.8 no.3
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• pp.219-236
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• 2023

In this paper, finite element modeling of the laser ultrasonics (LU) process in ablation regime is of interest. The momentum resulting from the removal of material from the specimen surface by the laser beam radiation in ablation regime is modeled as a pressure pulse. To model this pressure pulse, two equations are required: one for the spatial distribution and one for the temporal distribution of the pulse. Previous researchers have proposed various equations for the spatial and temporal distributions of the pressure pulse in different laser applications. All available equations are examined and the best combination of the temporal and spatial distributions of the pressure pulse that provides the most accurate results is identified. This combination of temporal and spatial distributions has never been used for modeling laser ultrasonics before. Then by using this new model, the effects of variations in pulse duration and laser spot radius on the shape, amplitude, and frequency spectrum of ultrasonic waves are studied. Furthermore, the LU in thermoelastic regime is simulated by this model and compared with LU in ablation regime. The interaction of ultrasonic waves with a defect is also investigated in the LU process in ablation regime. Good agreement of the results obtained from the new finite element model and available experimental data confirms the accuracy of the proposed model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.667-668
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• 2006

Usually nanosecond pulsing laser ablation of metal is under thermal effect. Many studies of the theoretical analysis and modeling to predict a result of laser ablation of metal are suggested on the basis of the photothermal mechanism. In this paper, we investigate the etching depth and laser fluence of laser ablation of copper films. We proposed the simplified SSB Model(Srinivasan-Smrtic-Babudp model) to study the photothermal effect of nanosecond pulsing laser ablation of copper thin metal. The experimental results were obtained by using the 355nm DPSS $Nd:YVO_4$ laser.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.2 s.191
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• pp.134-139
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• 2007

Usually nanosecond pulsed laser processing of metal is mainly affected by the thermal ablation. Many studies of the theoretical analysis and modeling to predict the laser ablation of metal are suggested on the basis of the photothermal mechanism at higher laser fluence. In this paper, we investigate the etching depth and laser fluence of laser ablation of copper foils and propose the simplified SSB Model(Srinivasan-Smrtic-Babu model) to study the photothermal effect of nanosecond pulsed laser ablation. The experimental results show that the photothermal ablation of the 355nm DPSS $NdYVO_{4}$ laser is useful to process the copper thin foils.

• Laser Solutions
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• v.11 no.4
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• pp.13-20
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• 2008

The damage threshold measurement of gold films is carried out with ultrashort-pulse laser. An enhanced two temperature model is developed to encounter the limitation of linear modeling during ultrashort pulse laser ablation. In which the electron heat capacity is calculated using a quantum mechanical approach based on a Fermi-Dirac distribution, temperature-dependent electron thermal conductivity valid beyond the Fermi temperature is adopted, and reflectivity and absorption coefficient are estimated by applying a temperature-dependent electron relaxation time. The predicted damage threshold using the proposed enhanced modelclosely agreed with experimental results, demonstrating the importance of considering transient thermal and optical properties in the modeling of ultrashort pulse laser ablation.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.138-143
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• 2017

A performance analysis for a pulsed plasma thruster(PPT) has been conducted to predict the thrust and current change. Two models were implemented - a one-dimensional lumped circuit analysis model and the Teflon ablation model provided by Michael Keidar. The circuit model incorporating resistance and inductance models was adapted to predict the magnitude of the discharge current. Numerical simulations like current discharge rates with different voltages were reasonably well compared with experimental data. The effects of Teflon ablation on thruster characteristics were investigated.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2163-2165
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• 2005

A pulsed laser ablation deposition (PLAD) technique has been used for producing fine particle as well as thin film at relatively low substrate temperatures. However, in order to manufacture and evaluate such materials in detail, motions of plume particles generated by laser ablation have to be understood and interactions between the particles by ablation and gas plasma have to be clarified. Therefore, this paper was focused on the understanding of plume motion in laser ablation assisted by Ar plasma at 50(mTorr). Two-dimensional hybrid model consisting of fluid and particle models was developed and three kinds of plume particles which are carbon atom (C), ion $(C^+)$ and electron were considered in the calculation of particle method It was obtained that ablated $C^+$ was electrically captured in Ar plasmas by strong electric field (E). The difference between motions of the ablated electrons and $C^+$ made E strong and the collisional processes active.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1408-1409
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• 2007

In this paper, we developed a hybrid simulation model of carbon laser ablation under the Ar plasmas consisted of fluid and particle methods. Three kinds of carbon particles, which are carbon atom, ion and electron emitted by laser ablation, are considered in the computation. In the present modeling, we adopt capacitively coupled plasma with ring electrode inserted in the space between the substrate and the target, graphite. This system may take an advantage of ${\mu}m$-sized droplets from the sheath electric field near the substrate. As a result, in Ar plasmas, carbon ion motions were suppressed by a strong electric field and were captured in Ar plasmas. Therefore, a low number density of carbon ions were deposited upon substrate. In addition, the plume motions in Ar gas atmosphere was also discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.349-352
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• 2007

In this paper, we describe the modeling of ablation based laser applications for innovative use in the military In the laser ignition system, a metal confinement is ablated with the high intensity pulsed energy, triggering a thermal ignition of the confined high explosives. The constitutive equations for the laser source, deformation of metals, and explosion of energetic materials are described.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.9
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• pp.642-648
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• 2019

In this study, Image-based computational analysis using the developed models was performed to predict the degradation of effective properties by ablation. The ablation tests of carbon/phenolic composites were performed using a 0.4 MW arc-heated wind tunnel. The carbon/phenolic composite samples were scanned using the micro-computed tomography (Micro-CT) to analyze the ablation characteristics according to a duration time of the ablation test. By calibrating the scanned images, computational models were developed that reflect the actual microstructure of the ablation composites. Also, nine computational models that reflect the actual pore shape were developed using the created cross-sectional images. Image-based computational analysis using the developed models was performed to predict the degradation of effective properties by ablation and the decrease of effective properties was confirmed with increase of porosity.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.60-68
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• 2005

To investigate the effects of beam focusing in the etching of polymers with short pulse Excimer lasers, a polymer etching model of SSB's is combined with a beam focusing model. Through the numerical simulation, it was found that in the high laser fluence region, SSB model considering both photochemical and thermal contribution is considered to be suitable to predict the etched hole shape than a simple photochemical etching model. The average temperature distribution into the substance obtained by assuming 1-D heat transfer is found to be fairly similar to the fluence distribution on the ablated surface. The experimental etching data fur polymers are used to give material properties for ablation model. The fitted etch depth curve gives a nice agreement with the experimental data.