• Proceedings of the Korean Society of Laser Processing Conference
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• 2003.05a
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• pp.103-106
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• 2003

• Journal of the Korean Society for Precision Engineering
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• v.26 no.5
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• pp.150-156
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• 2009

The removal of tiny particles adhered to surfaces is one of the crucial prerequisite for a further increase in IC fabrication, large area displays and for the process in nanotechnology. Various cleaning techniques (wet chemical cleaning, scrubbing, pressurized jets and ultrasonic processes) currently used to clean critical surfaces are limited to removal of micrometer-sized particles. Therefore the removal of sub-micron sized particles from silicon wafers is of great interest. For this purpose various cleaning methods are currently under investigation. In this paper, we report on experiments on the cleaning effect of 100nm sized fluorescence particles on silicon wafer using the plasma shockwave occurred by femtosecond laser. The plasma shockwave is main effect of femtosecond laser cleaning to remove particles. The removal efficiency was dependent on the gap distance between laser focus and surface but in some case surface was damaged by excessive laser intensity. These experiments demonstrate the feasibility of femtosecond laser cleaning using 100nm size fluorescence particles on wafer.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.3
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• pp.68-71
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• 2008

Transdermal and topical drug delivery with minimal tissue damage has been an area of vigorous research for a number of years. Our research team has initiated the development of an effective method for delivering drug particles across the skin (transdermal) for systemic circulation, and to localized (topical) areas. The device consists of a micro particle acceleration system based on laser ablation that can be integrated with endoscopic surgical techniques. A layer of micro particles is deposited on the surface of a thin metal foil. The rear side of the foil is irradiated with a laser beam, which generates a shockwave that travels through the foil. When the shockwave reaches the end of the foil, it is reflected as an expansion wave and causes instantaneous deformation of the foil in the opposite direction. Due to this sudden deformation, the microparticles are ejected from the foil at very high speeds, and therefore have sufficient momentum to penetrate soft body tissues. We have demonstrated this by successfully delivering cobalt particles $3\;{\mu}m$ in diameter into gelatin models that represent soft tissue with remarkable penetration depth.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.05a
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• pp.24.2-24.2
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• 2007

• Composites Research
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• v.37 no.1
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• pp.21-31
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• 2024

This review paper investigates the use of shockwave attenuating materials within composite structures to enhance personnel protection against blast-induced traumatic brain injury (bTBI). This paper also introduces experimental methodologies exploited in the generation and measurement of shockwaves to evaluate the performance of the shock dissipating composites. The generation of shockwaves is elucidated through diverse approaches such as high-energy explosives, shock tubes, lasers, and laser-flyer techniques. Evaluation of shockwave propagation and attenuation involves the utilization of cutting-edge techniques, including piezoelectric, interferometer, electromagnetic induction, and streak camera methods. This paper investigates phase-separated materials, including polyurea and ionic liquids, and provides insight into composite structures in the quest for shockwave pressure attenuation. By synthesizing and analyzing the findings from these experimental approaches, this review aims to contribute valuable insights to the advancement of protective measures against blast-induced traumatic brain injuries.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.365-368
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• 2009

A new concept of a small thruster for altitude control of a micro/nano class satellite is developed, which utilizes the pulsed laser energy. As the laser-based thruster does not require burning of any fuel, it gives promise of small satellite design criteria, namely light weight and cost effectiveness. In this paper, we develop gel-type material for generating strong plasma plume for enhancing thrust for propulsion. Moreover, we quantify the level of thrust via the momentum coupling coefficient measured by the pendulum system. We discover that the driving force is significantly improved via the gel-typed propellant for laser ablation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1041-1046
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• 2011

Micro shockwaves are induced in laser shock peening and their effect on metal samples is presented. Laser shock peening produces maximized internal compressive stress on metal surfaces. This research evaluated the effects of micro shockwaves from laser shock peening with a pulsed Nd:YAG laser on steel samples, through the analysis of the mechanical properties of the samples. In the experiments, a piezo material was applied to measure the micro shockwaves and the hardnesses and micro tensile strengths of the samples were evaluated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.67-71
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• 2010

Impingement of a high power laser pulse (above 1 GW/$cm^2$) on a metal foil causes its ablation, which is characterized by a rapid expulsion of matter and the initiation of a strong shock wave inside the solid metal. The shock propagates through the foil and reverberates on the rear side, causing its deformation and microparticle ejection, which were deposited on the foil prior to ablation. Based on this principle, we are developing a new drug delivery system - Biolistic gun. Current study is focused on the controllability, stability, efficiency of the system, and characterization of the penetration shapes in various conditions. We have tested the system by applying direct and confined ablation. Several different media combinations were used for confinement-BK7 glass, water, BK7 glass with water, and succulent jelly(ultrasono jelly, RHAPAPHRM). Biological tissue was replicated by a 3% gelatin solution. Present data shows that the confinement results in enhancement of penetration shape reached by 5 um cobalt microparticles. Based on the analysis of the experimental results we observe that the penetration shape of microparticles can be controlled by adjusting the thickness of confinement media.