• Bulletin of the Korean Chemical Society
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• v.19 no.11
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• pp.1172-1174
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• 1998

Spatial(radial and height) distributions of excited argon species are measured for an inductively coupled plasma under five operating conditions: 1) no carrier gas, 2) carrier gas without aerosol, 3) carrier gas with desolvated aerosol, 4) carrier gas with aerosol, 5) carrier gas with aerosol and excess lithium. A complete RF power mapping of argon excited states is obtained. The excited states of argon for a typical analytical torch rapidly diffuse towards the center in the higher region of the plasma. The presence of excess lithium makes no significant change in the excited states of argon. The increase in the RF power increases the intensity of argon excited states uniformly across the radial coordinate.

• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.267-274
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• 2001

Removal of Cr, Ni and Cu impurities on Si surfaces using remote plasma-excited hydrogen was investigated. Si surfaces were contaminated intentionally by acetone with low purity. To determine the optimum process condition, remote plasma-excited hydrogen cleaning was conducted for various rf-powers and plasma exposure times. After remote plasma-excited hydrogen cleaning, Si surfaces were analyzed by Total X-ray Reflection Fluorescence(TXRF), Surface Photovoltage(SPV) and Atomic Forece Microscope(AFM). The concentrations of Cr, Ni and Cu impurities were reduced and the minority carrier lifetime increased after remote plasma-excited hydrogen. Also RMS roughness decreased by more than 30% after remote plasma-excited hydrogen cleaning. AFM analysis results also show that remote plasma-excited hydrogen cleaning causes no damage to the Si surface. TXRF analysis results show that remote plasma-excited hydrogen cleaning is effective in eliminating metallic impurities from Si surface only if it is performed under an optimum process conditions. The removal mechanism of the Cr, Ni and Cu impurities using remote plasma-excited hydrogen treatments is proposed to be the lift-off during removal of underlying chemical oxides.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.424-428
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• 2003

We have developed the RF discharge Excited slab Waveguide $CO_2$ laser and measured the output power. We make used of concave and concave mirror, concave and convex mirror that negative branch and positive branch unstable resonator, respectively. The resonator active dimension is 2$\times$40$\times$400 mm and ratio frequency is 123 MHz. The gas mixing ratio is $CO_2$: $N_2$ : He=1 : 1 : 3. The pressure in resonator is from 10 to 60 torr and RF input power increased from 100 to 900 W. so that We obtained laser maximum output power of negative branch and positive branch resonator 50.9 W and 70.8 W and efficiency is 6.5 % and 9.2 %, respectively.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.406-412
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• 2003

We have developed a radio frequency excited slab waveguide $CO_2$ laser. The dimension of active volume is 2${\times}$40${\times}$400 mm. One concave and one convex mirror are used to make the unstable resonator of the positive branch. The radio frequency is 123 MHz and RF input power is varied from 100 to 900 W. The laser gas is set to a pressure of 10∼60 torr and the mixing ratio is $CO_2$:$N_2$:He=1:1:3. The laser output power of 70.7 W was obtained which corresponds to laser power to RF power conversion efficiency of 9.2%.

• Proceedings of the Korean Vacuum Society Conference
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• 1994.02a
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• pp.80-81
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• 1994

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.337-342
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• 2004

Laser optical power stabilization of a radio frequency excited $CO_2$ slab laser using the opto-Hertzian effect generated from the laser itself is achieved on the peak of the Doppler broadened gain curve. The opto-Hertzian signal was generated by a modulation of the optical flux circulating inside the laser cavity from a variation in the cavity length caused by the vibrations of the PZT. The opto-Hertzian signal is directly coupled from a RE discharge chamber via a loop antenna into a detector and applied to a lock-in stabilizer as an reference signal. The power stability of an RF excited slab laser is estimated to be better then 0.2%.

• Investigative Magnetic Resonance Imaging
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• v.3 no.1
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• pp.13-19
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• 1999

MRI imaging provides many benefits such as noninvasive, 3-dimensional imaging capabilities. But it has relatively serious drawback that is the long data collection time, compared with other imaging modality. Many studies have been performed for fast MR imaging. But EPI and SEPI (4-6) are required to expensive hardware. In this paper, we introduce to Burst imaging technique. It can reduce imaging time by use of a mulitple RF excitation technique. Further it is easily implemented to the normal MRI system. But a pixel profile in the conventional burst sequence is so poor that excited area by burst sequence is a small portion of a pixel. This causes poor signal to noise ratio in burst image. therefore frequency sweeping of RF pulse for burst imaging sequence is proposed to improve pixel profile. A burst pulse train is shaped by liner or nonlinear frequency sweeping function so that all the spins within a pixel are excited, thereby improving the signal to noise ratio. It also shows that the pixel profiles are dependent on how frequency sweep is made. Computer simulations with Bloch equation and experimental results obtained using a 1.0 T NMR imaging system are presented.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.513-514
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• 2005

In plasma processing reactors, it is common practice to control plasma density and ion bombardment energy by manipulating excitation voltage and frequency. In this paper, a dually excited capacitively coupled rf plasma reactor is self-consistently simulated with a three moment model. Effects of phase differences between primary and secondary voltage waves, simultaneously modulated at various combination of commensurate frequencies, on plasma properties are investigated. The simulation results show that plasma potential and density as well as primary self-dc bias are nearly unaffected by the phase lag between the primary and the secondary voltage waves. The results also show that, with the secondary frequency substantially lower than the primary frequency, secondary self-dc bias remains constant regardless of the phase lag. As the secondary frequency approaches to the primary frequency, however, the secondary self-dc bias becomes greatly altered by the phase lag, and so does the ion bombardment energy at the secondary electrode. These results demonstrate that ion bombardment energy can be more carefully controlled through plasma simulation.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.234-238
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• 1992

A sealed-off waveguide $CO_2$ laser with a length of 50 cm and a cross-sectional area of $6\times 6\ttextrm{mm}^{2}$ has been designed and constructed. The laser is transversely excited by RF (13.56 MHz) discharge. Output characteristics of the laser has been investigated performing variations of total gas pressure, input rf power, and mixing ratios of gases. The maximum output power of 9.5 W was obtained under the condition of total gas pressure of 50 Torr, input rf power of 180 W, and gas mixture of 6 : 1 : 2 : 1 of $He:CO_{2}:N_{2}:Xe$.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.270-271
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• 2003

링 레이저 자이로스코프는 회전각을 검출하는 센서로서 광학식이 가지는 정밀함과 견고성으로 관성항법을 비롯한 운동 제어를 필요로 하는 여러 분야에서 기존의 기계식 자이로스코프를 대체해 오고 있다. 링 레이저 자이로는 세 개 또는 네 개의 반사경으로 밀폐된 고리형 공진기를 구성하고 He-Ne 기체를 봉입하여 방전시킴으로써 서로 반대 방향으로 진행하는 레이저를 동시에 발진시키면 Sagnac 효과에 의해 공진기의 회전각에 비례하여 두 레이저의 주파수 차이가 발생하는 원리를 이용한다. (중략)