• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.287-293
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• 2004

A numerical simulation is presented for investigating the effects of pressure ratio of $D_2$ injector to supersonic nozzle on the population inversion in the DF chemical laser cavity, while a lasing concurrently takes place. The laser beam is generated between the mirrors in the cavity and it is important to obtain stronger population inversion and more uniform distribution of the excited molecules in the laser cavity in order to produce high power laser beam with good quality. In this study, these phenomena are investigated by means of analyzing the distributions of the DF excited molecules and the F atom used as an oxidant, while simultaneously estimating the maximum small signal and saturated gains and power in the DF chemical laser cavity. For the numerical solution, an 11-species (including DF molecules in various excited states of energies), 32-step chemistry model is adopted for the chemical reaction of the DF chemical laser system. The results are discussed by comparison with two $D_2$injector pressure cases; 192 torr and 388.64 torr. Major results reveal that in the resonator, stronger population inversions occur in the all transitions except DF(1)-DF(0), when the $D_2$injection pressure is lower. But, the higher $D_2$injection pressure provides a favorable condition for DF(1)-DF(0) transition to generate the higher power laser beam. In other words, as the pressure of $D_2$injector increases, the maximum small signal gain in the $V_{1-0}$ transition, which is in charge of generating most of laser power, becomes higher. Therefore, the total laser beam power becomes higher.r.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2002.01a
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• pp.6-6
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• 2002

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.9
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• pp.789-795
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• 2016

Laser-induced combustions and explosions generated by high laser irradiances were explored by Laser-Induced Breakdown Spectroscopy (LIBS). The laser used for target ablation is a Q-switched Nd:YAG laser with 7 ns pulse duration at wavelength of 1064 nm laser energies from 40 mJ to 2500 mJ ($6.88{\times}10^{10}-6.53{\times}10^{11}W/cm^2$). The plasma light source from aluminum detected by the echelle grating spectrometer and coupled to the gated ICCD(a resolution (${\lambda}/{\Delta}{\lambda}$) of 5000). This spectroscopic study has been investigated for obtaining both the atomic/molecular signals of aluminum-oxygen and the calculated ambient condition such as plasma temperature and electron density. The essence of the paper is observing specific electron density ratio which can support the processes of chemical reaction and combustion between ablated aluminum plume and oxygen from air by inducing high laser energy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.430-433
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• 2005

Laser bonding between similar and dissimilar thermoplastics has been investigated by making use of laser transmission weld technique. Spot welding of two layers of plastic materials has been demonstrated by using of a high-quality diode-laser with 808nm wavelength. Weld areas increases according to power density, exposure time. The results of peel out test show that peel strengths increase with the area of molten plastics. Layers, which have the same chemical properties, have good bonding qualities. A bonding method which dye film is coated on the interface is used for laser bonding between plastics with high transmission for laser wavelength. Laser transmission bonding is worthy of attention because it is not in contact, requires a few tooling devices, allows a flexible energy delivery and produces nearly invisible welds

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.3
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• pp.217-221
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• 2004

[ $CO_2$ ]laser ablation rates for bulk 4H-SiC substrates and GaN/AIN/SiC templates in the range 229-870 ${\mu}m.min^{-1}$ were obtained for pulse energies of 7.5-30 mJ over diameters of 50·500 ${\mu}m$ with a Q-switched pulse width of ${\sim}30$ nsec and a pulse frequency of 8 Hz. The laser drilling produces much higher etch rates than conventional dry plasma etching (0.2 - 1.3 ${\mu}m/min$) making this an attractive maskless option for creating through-wafer via holes in SiC or GaN/AlN/SiC templates for power metal-semiconductor field effect transistor applications. The via entry can be tapered to facilitate subsequent metallization by control of the laser power and the total residual surface contamination can be minimized in a similar fashion and with a high gas throughput to avoid redeposition. The sidewall roughness is also comparable or better than conventional via holes created by plasma etching.

• Current Optics and Photonics
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• v.8 no.2
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• pp.138-150
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• 2024

This study is essential for advancing our knowledge about the interaction between long-range high-power lasers and energetic materials, with a particular emphasis on understanding the response of a 155-mm shell under various surface irradiations, taking into account external factors such as atmospheric disturbances. The analysis addresses known limitations in understanding the use of non-realistic targets and the negligence of ambient conditions. The model employs the three-dimensional level-set method, computer-aided design (CAD)-based target design, and a message-passing interface (MPI) parallelization scheme that enables rapid calculations of the complex chemical reactions of the irradiated high explosives. Important outcomes from interaction modeling include the accurate prediction of the initiation time of ignition, transient pressure, and temperature responses with the location of the initial hot spot within the shell, and the relative magnitude of noise with and without the presence of physical ambient disturbances. The initiation time of combustion was increased by approximately a factor of two with atmospheric disturbance considered, while slower heating of the target resulted in an average temperature rise of approximately 650 K and average pressure increase of approximately 1 GPa compared to the no ambient disturbance condition. The results provide an understanding of the interaction between the high-power laser and energetic target at a long distance in an atmospheric condition.

• Bulletin of the Korean Chemical Society
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• v.10 no.1
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• pp.96-101
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• 1989

The infrared multiphoton decomposition of trichloroethylene-H(TCE-H) and trichloroehtylene-D(TCE-D) was studied by using the high power $CO_2$ laser. The pressure dependence of TCE-H decomposition showed that the HCl elimination channel to form ClC ≡ CCl was the major step at high pressures, while the HC ≡ CCl formation step became important at low pressures. $Cl_2C$ = CHCl ${\rightarrow}$ (high pressure) ClC ${\equiv}$ CCl + HCl ${\rightarrow}$ (low pressure) HC ${\equiv}$ CCl + 2Cl${\cdot}$($Cl_2$) The IRMPD of TCE-H and TCE-D mixtures with 10P(20) laser line showed that optimum conditions of large isotope selectivity were the low system pressures and high laser powers. The experimentally observed dependence of the branching ratios on the pressure and laser fluence, and the isotope selectivity coefficients were quantitatively explained by using the modified energy grained master equations (EGME) model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.197-204
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• 2012

We explore the evolution of metal plasma generated by high laser irradiances and its effect on the surrounding air by using shadowgraph images after laser pulse termination and X-ray diffraction (XRD) of aluminum plasma ablated by a high-power laser pulse (>1000 mJ/pulse) and oxygen from air. Hence, the formation of laser-supported detonation and combustion processes has been investigated. The essence of this paper is in observing the initiation of chemical reaction between the ablated aluminum plasma and oxygen from air by the high-power laser pulse (>1000 mJ/pulse) and in conducting a quantitative comparison of the chemically reactive laser-initiated waves with the classical detonation of an exploding aluminum (dust) cloud in air. The findings in this work may lead to a new method of initiating detonation from a metal sample in its bulk form without any need to mix nanoparticles with oxygen for initiation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.425-429
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• 2011

The development of metal plasma generated by high laser irradiance and its effect on the surrounding air using shadowgraph images after laser pulse termination are studied; hence the formation of laser supported detonation and combustion processes has been investigated. The core of the paper is in detecting chemical reaction using X-Ray Diffraction (XRD) between ablated aluminum plasma and oxygen from air by inducing high power laser pulse (>1000 mJ/pulse) and conduct a quantitative comparison of chemically reactive laser initiated waves with the classical detonation of exploding aluminum (dust) cloud in air. This study may suggest a new approach of initiating detonation from metal sample in its bulk form without the need of mixing nano-particles with oxygen for initiation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.4
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• pp.291-296
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• 2020

The high power of a shingled photovoltaic module can be attributed to its low cell-to-module loss. The production of high power modules in limited area requires high efficiency solar cells. Shingled photovoltaic modules can be made by divided solar cells, which can be produced by the laser scribing process. After dividing the 21% PERC cell using laser scribing, the efficiency decreased by approximately 0.35%. However, there was no change in the efficiency of the solar cell having relatively lower efficiency, because the laser scribing process induce higher heat damages in solar cells with high efficiency. To prove this phenomena, the J₀ (leakage current density) of each cell was analyzed. It was found that the J₀ of 21% PERC increased about 17 times between full and divided solar cell. However, the J₀ of 20.2% PERC increased only about 2.5 times between full and divided solar cell.