• Journal of Korean Dental Science
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• 제10권2호
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• pp.66-73
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• 2017

Purpose: To evaluate the effect of different-sized drill tips and laser irradiation times on the initial stability of orthodontic miniscrews placed in Er,Cr:YSGG-laser pre-drilled holes in an animal model. Materials and Methods: Laser pre-drilled holes were made in dog mandibular bone with an Er,Cr:YSGG laser using irradiation times of 5, 7, 9, 11, and 13 seconds, and tip diameters of 0.4 and 0.6 mm. The maximum diameter and depth of the pre-drilled holes was measured with micro computed tomography. The maximum insertion torque was measured during placement the miniscrew. Result: Laser pre-drilled holes were conical shaped. The maximum diameter of pre-drilled holes increased with longer laser irradiation times (P>0.05) and larger tip diameters (P<0.05). The depth of pre-drilled holes increased with longer laser irradiation times and larger tip diameters (P<0.05). When the 0.4 mm tip, but not the 0.6 mm tip, was used, the insertion torque decreased significantly with longer laser irradiation times (P<0.05). Conclusion: Tip diameter impacted insertion torque more than irradiation time. It takes at least 9 seconds using a 0.6 mm tip to create a 0.8 mm diameter and 1.0 mm depth hole in thick cortical bone.

• 한국정밀공학회지
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• 제30권10호
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• pp.1017-1022
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• 2013

Currently, various optical fiber tips are used to deliver laser beam for endoscopic surgery. In this paper, we demonstrated multidirectional (forward and side) firing optical fiber tip using a femtosecond micromachining and $CO_2$ laser polishing technology. We controlled the edge width of optical fiber tip, by modulating the condition of $CO_2$ laser, to regulate the amount of side and forward emission. The distal end of the optical fiber with core/clad diameter of $400/440{\mu}m$ was microstructured with cone shape by using a femtosecond laser. And then the microstructured optical fiber tip was polished by $CO_2$ laser beam result in smoothing and specular reflection at the surface of the cone structure. Finally, we operated the LightTools simulation and good agreement was generally found between the proposed model and experimental simulation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.154-154
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• 2000

FED(Field emission display)의 FEAs(Field emitter arrays)에 형성되어 있는 micro-tip 은 tip 표면의 오염이나 진공내부의 잔류가스에 대단히 민감하다. 특히, emitter 물질의 일함수 및 겉모양 같은 기하학적 요소에 민감한 전계방출 소자의 특성상 tip 선단이 oxidation 될 경우 일함수가 증가하여 전자방출에 필요한 구동전압이 증가하고 전자 방출의 불균일성이 커지는 문제점이 발생한다. 이에 고진공의 동작 환경 및 FEAs 제작과정이나 공기의 노출에 발생하는 tip 표면의 오염물질 제거가 요구된다. 따라서 본 연구에서는 40$\times$40mm2 FEAs에 laser power, scan speed을 달리하며 laser(cw Nd-YAG, 1064nm)을 조사하였다. laser cleaning 효과를 보기 위해 laser irradiation 전, 후에 진공도 5$\times$10-7torr irradiation 후에 emitter tip의 뚜렷한 기하학적 모양의 변화를 볼 수는 없었지만, I-V 특성이 향상 되는 것을 볼 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제40권4호
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• pp.237-245
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• 2023

Laser communication has been considered as a novel method for earth observation satellites with generation of high data volume. It offers faster data transmission speeds compared to conventional radio frequency (RF) communication due to the short wavelength and narrow beam divergence. However, laser beams are refracted due to atmospheric turbulence between the ground and the satellite. Refracted laser beams, upon reaching the receiver, result in angle-of-arrival (AoA) fluctuation, inducing image dancing and wavefront distortion. These phenomena hinder signal acquisition and lead to signal loss in the course of laser communication. So, precise alignment between the transmitter and receiver is essential to guarantee effective and reliable laser communication, which is achieved by pointing, acquisition, and tracking (PAT) system. In this study, we simulate the effectiveness of tip/tilt compensation for more efficient laser communication in the satellite-ground downlink. By compensating for low-order terms using tip/tilt mirror, we verify the alleviation of AoA fluctuations under both weak and strong atmospheric turbulence conditions. And the performance of tip/tilt correction is analyzed in terms of the AoA fluctuation and collected power on the detector.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.891-894
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• 2014

The ultrashort electron pulse, laser-emitted from the metal tip apex has been characterized and used as a probing source for a new electron microscope to visualize the morphology of the gold-mesh in the nanometric resolution. As the gap between the tungsten tip and Au-surface is approached within a few nm, the large electromagnetic field enhancement for the incident P-polarized laser pulse with respect to the tip-sample axis is strongly observed. Here, we demonstrate that the time-resolved tip-enhanced electron emission microscope (TEEM) can be implemented on the laboratory table top to give the two-dimensional image, opening lots of challenges and opportunities in the near future.

• 한국레이저가공학회지
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• 제18권1호
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• pp.18-22
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• 2015

In this paper, controlling shape of optical fiber tip for endoscope was investigated for eliminating blind spot. The blind spot of endoscope is generated by divergence angle of optical fiber, so it is easy to generate blind spot when tightly focusing. In order to eliminate this region, fiber tip is necessary to be controlled as convex or concave. Illumination simulation of convex and concave type of fiber tip in the endoscope was in progress, so the distance of non- blind region was investigated in each case. As well as the simulation, the tip was fabricated as concave shape by UV laser machining. Then the beam radiation was measured to observe the blind region. The result showed that controlling the fiber tip as convex or concave shape makes the narrow blind region of illumination in endoscope.

• 대한치과보철학회지
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• 제46권3호
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• pp.255-260
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• 2008

STATEMENT OF PROBLEM: Preparation of implant beds with lasers is considered a safe and reliable method, but the accuracy of this technique has not been examined. PURPOSE: The purpose of this study was to evaluate the accuracy and effectiveness of implant bed preparation using an Er,Cr:YSGG laser. MATERIAL AND METHODS: An Er,Cr:YSGG laser was applied to pig rib bone. The laser was employed at a 5.75 W power setting, 30 Hz/sec pulse repetition, and 70 ${\mu}s$ pulse duration with 50 % water and 60% air spray. According to laser tips the groups were divided as follows; Group 1: paralleled - shaped sapphire tip (0.6 mm${\Phi}$), Group 2: paralleled - shaped zirconia tip (0.6 mm${\Phi}$), Group 3: tapered sapphire tip (0.4 mm${\Phi}$). The Er,Cr:YSGG laser tip was separated by 1 mm from the bone and applied for 15 seconds in a non-contact mode. After the application, the bone was sectioned for specimens. Histologic measurements were determined by computerized morphometry. The length of the prepared bone surface was measured and the width of the entrance was measured. The results were analyzed with one-way ANOVA (P<0.05). RESULTS: The prepared length of group 3 was longer than that of group 2. The prepared bone width was larger than the width of the laser tip in every group. Additional bone removal was observed adjacent to the prepared area and displayed an irregular surface. CONCLUSION & DISCUSSION: Different cutting effects were observed according to the laser tip, emphasizing the importance of proper tip selection in the clinical setting. This preliminary study supported the existence of hydrokinetic effects.

• Journal of Welding and Joining
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• 제21권3호
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• pp.58-67
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• 2003

In this study, the formation mechanism of discontinuities in the laser fusion zone of diamond saw blade was investigated. $CO_2$ laser weldings were conducted along the butt between Fe base sintered tip and carbon steel shank with sets of variable welding parameters. The effect of heat input on irregular humps, outer cavity, inner cavity and bond strengh was evaluated. The optimum heat input to have a proper humps was in the range of 10.4~$17.6kJm_{-1}$. With increasing heat input, both outer and inner cavities were reduced. The outer cavity was caused by insufficient refill of keyhole, while inner cavity was caused by trapping of bubble in molten metal. The bubble came from sintered tip and intensive vaporization at bottom tip of the keyhole. A gas formation and low melting point element vaporization were not occurred during welding. We could not find any relationship between bond strength and amount of discontinuities. Because the fracture were occurred in not only sintered tip but also carbon steel shank due to hardness distributions.

• 한국레이저가공학회지
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• 제7권3호
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• pp.25-36
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• 2004

This study was performed to clarification of the formation of weld discontinuities in the dissimilar laser fusion zone. Welding parameters were beam power of 1300, 1430, 1560, and 1700 W and travel speed of 1, 1.3, and 1.7 m/min. Most cavities in the fusion zone were observed near the tip. Cavities in the fusion zone observed to be formed and grown from pores in the tip. More cavities were formed as the beam position moves to the tip side. Small cavities were decreased but large cavities were increased when the energy input increased. W content in the fusion zone was increased with heat input and as the beam position close to the tip. In the fusion zone, W content in the dendrite boundary was increased with heat input. Considering the propagation path and fracture morphology, cracks were solidification cracking, and were initiated and propagated along the dendrite boundaries. The formation of cracks might be related with the W rich ${\mu}$ phase which was formed in the grain boundaries and dendrite boundaries.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.149-150
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• 2006

We describe a novel method of scanning probe nanofabrication using a AFM(atomic force microscopy) tip with assistance of Femtosecond laser pulses to enhance fabrication capability. Illumination of the AFM tip with ultra-short light pulses induces a strong electric field between the tip and the metal surface, which allows removing metal atoms from the surface by means of field evaporation. Quantum simulation reveals that the field evaporation is triggered even en air when the induced electric field reaches the level of a few volts per angstrom, which is low enough to avoid unwanted thermal damages on most metal surfaces. For experimental validation, a Ti: sapphire Femtosecond pulse laser with 10 fs pulse duration at 800 nm center wavelength was used with a tip coated with gold to fabricate nanostructures on a thin film gold surface. Experimental results demonstrate that fine structures with critical dimensions less than ${\sim}10nm$ can be successfully made with precise control of the repetition rate of Femtosecond laser pulses.