• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1572-1577
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• 2003

High-power pulsed laser ablation under atmospheric pressure is studied utilizing numerical and experimental methods with emphasis on recondensation ratio, and the dynamics of the laser induced vapor flow. In the numerical calculation, the temperature pressure, density and vaporization flux on a solid substrate are first obtained by a heat-transfer computation code based on the enthalpy method, and then the plume dynamics is calculated by using a commercial CFD package. To confirm the computation results, the probe beam deflection technique was utilized for measuring the propagation of a laser induced shock wave. Discontinuities of properties and velocity over the Knudsen layer were investigated. Related with the analysis of the jump condition, the effect of the recondesation ratio on the plume dynamics was examined by comparing the pressure, density, and mass fraction of ablated aluminum vapor. To consider the effect of mass transfer between the ablation plume and air, unlike the most previous investigations, the equation of species conservation is simultaneously solved with the Euler equations. Therefore the numerical model computes not only the propagation of the shock front but also the distribution of the aluminum vapor. To our knowledge, this is the first work that employed a commercial CFD code in the calculation of pulsed ablation phenomena.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1483-1491
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• 2001

Enhancement of pulsed-laser ablation by an artificially deposited liquid film is presented. Measurements of ablation rate, ablation threshold, and surface topography arc performed. Correlation between material ablation and photoacoustic effect is examined by the optical beam deflection method. The dependence of ablation rate on liquid-film thickness and chemical composition is also examined. The results indicate that photomechanical effect in the phase explosion of liquid is responsible for the enhanced ablation. The low critical temperature of liquid induces explosive vaporization with localized photoacoustic excitation in the superheat limit and increases the ablation efficiency. Experiments were carried out utilizing a Q-swiched Nd:YAG laser at near-threshold laser fluences with negligible plasma effect (up to ∼100 MW/cm$^2$).

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.285-288
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• 2007

Numerical study of the influence of the boundary layer of micro-supersonic jet impinging on a flat plate with a hole was performed, to investigate the role of gas jet to eject melted materials from the cut zone in the laser machining. The detailed shock structures and the information of the mass flow rate through the hole were compared to the results of the previous study, in which the effects of boundary layer inside nozzle was not accounted. It was found that the boundary layer inside the micro- nozzle introduced stronger Mach disc over the machining zone, and thus that the mass flow rate through the hole decreased.

• Current Optics and Photonics
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• v.7 no.6
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• pp.714-720
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• 2023

Laser cleaning has the advantages of environmental protection, precision, and high efficiency, and has good prospects for application in removing oxide films on the surface of aluminum alloy. This paper discusses the cleaning threshold and cleaning mechanism of aluminum alloy surface oxide film. A nanosecond pulsed laser was used to remove a 5-㎛-thick oxide film from the surface of 7A04 aluminum alloy, and the target surface temperature and cleaning depth were simulated. The effects of different laser energy densities on the surface morphology of the aluminum alloy were analyzed, and the plasma motion process was recorded using a high-speed camera. The temperature measurement results of the experiment are close to the simulation results. The results show that the laser cleaning of aluminum alloy oxide film is mainly based on the vaporization mechanism and the shock wave generated by the explosion.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.381-384
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• 2011

Wave drag reduction due to the repetitive laser induced energy deposition over a flat-nosed cylinder is experimentally conducted in this study. Irradiated laser pulses are focused by a convex lens installed in side of the in-draft wind tunnel of Mach 1.94. The maximum frequency of the energy deposition is limited up to 80. Time-averaged drag force is measured using a low friction piston which was backed by a load cell in a cavity as a controlled pressure. Stagnation pressure history, which is measured at the nose of the model, is synchronized with corresponding sequential schlieren images. With cylinder model, amount of drag reduction is linearly increased with input laser power. The power gain only depends upon the pulse energy. A drag reduction about 21% which corresponds to power gain of energy deposition of approximately 10 was obtained.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.256-259
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• 2003

To develop cleaning process various particles should be deposited on wafer surfaces to measure particle removal efficiencies. The purpose of the article in to evaluate, removal efficient)r of silica and alumina particles from wafer surfaces when they are deposited by dry and wet method. Dry deposition in air and wet spray deposition using solutions are used. van der Waals are considered to calculate the adhesion force of particles on surfaces. Higher adhesion force is measured on alumina particles on silicon when particles are deposited in air.

• Proceedings of the Materials Research Society of Korea Conference
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• 2006.05a
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• pp.20.1-20.1
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• 2006

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.5
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• pp.547-550
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• 2011

We have developed a laser-based needle-free liquid drug-injection device. A laser beam is focused inside the liquid contained in the rubber chamber of a micro-scale. The focused laser beam causes explosive bubble growth, and the sudden volume increase in a sealed chamber drives a microjet of liquid drug through the micronozzle. The exit diameter of a nozzle is less than 100 ${\mu}m$, and we verify that the injected microjet is fast enough to penetrate soft human tissue. In the experiment, the microjet penetrated a 5% gelatin-water solution that replicates the human thrombus and pork-fat tissue.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.166-173
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• 2003

This paper presents micromachining results on planar-lightwave-circuit (PLC) chips with Si substrate and the quartz substrate by using Ti:Sapphire femtosecond-pulsed laser. The ablation process with femtosecond laser pulses generates nothing of contamination, molten zone, microcracks, shock wave, delamination and recast layer. We also showed that the micromachine for PLC using femtosecond pulsed lasers is superior to that using nanosecond pulsed lasers. The insertion loss and the optical return loss of the 1 ${\times}$ 8 optical power splitters packaged with micromachined input- and output-port U-grooves were less than 11.0 ㏈ and more than 55 ㏈, respectively. The wavelength dependent loss (WDL) was distributed within $\pm$0.6 ㏈ and the polarization dependent loss (PDL) was less than 0.2 ㏈.

• The Journal of the Acoustical Society of Korea
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• v.38 no.4
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• pp.459-466
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• 2019

When a laser pulse is irradiated on a CNT (Carbon Nanotube) and PDMS (Poly dimethylsiloxane) composite coated on a transparent PMMA (Poly methyl methacrylate) substrate, a strong ultrasonic wave is generated due to the thermoelastic effect. In this paper, the thermoacoustic theory related to the wave generation by the CNT/PDMS composite was established. The waveforms of ultrasonic waves when a laser pulse having a Gaussian waveform is irradiated on the composite with a thickness of $20{\mu}m$ were numerically simulated. From the results, it was confirmed that ultrasonic shock waves can be generated from the CNT/PDMS composite and the waveforms are changed little even if the physical properties of the composite are changed by ${\pm}20%$. It was found that the peak positive and negative pressures increase as the thermal expansion coefficient increases, or as density, heat capacity and sound speed decreased. However, those changes were not so sensitive with thermal conductivity. In addition, the physical properties of the CNT/PDMS composite fabricated in this study were estimated from the comparison of the measurement and simulation results.