• 한국광학회지
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• 제21권6호
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• pp.254-258
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• 2010

타원형 모양의 모드 형태를 갖는 펄스형 레이저 다이오드 (laser diode)의 펄스 형태를 유지하면서 단일 모드 및 Gaussian 형태로 광 모드 변환을 유도하고 광출력을 증폭할 수 있는 기술에 대해서 연구하였다. 실험에서 사용한 펼스형 레이저 다이오드의 구경이 가로는 $300{\mu}m$이며, 세로는 $2{\mu}m$이고 출력은 $1.1mW/cm^2$이다. 렌즈형 광섬유를 사용하여 광결합을 유도하여 단일 모드 및 Gaussian 형태의 출력으로 변환시켰다. 그러나, 다중모드의 펄스형 레이저 다이오드의 출력을 단일모드 렌즈형 광섬유에 결합시키면 출력이 급격하게 감소한다. 따라서 master oscillator power amplifier (MOPA) 기반의 광증폭 기술을 이용하여 레이저 다이오드의 광출력을 증폭시켰다. 증폭 후에도 펄스 성질은 그대로 유지되었고, MOPA구조를 지나 증폭된 광 출력은 $29mW/cm^2$로 측정되었다.

• 한국광학회지
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• 제32권2호
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• pp.62-67
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• 2021

본 연구에서는 모드 잠금된 ps-펄스 광섬유 레이저와 연속 발진하는 좁은 선폭의 반도체 레이저를 이용하여 주기적 분극반전된 LiNbO3(periodically poled lithium niobate; PPLN) 결정에서 합주파수 생성 연구를 수행하였다. 모드 잠금된 펄스 레이저는 중심 파장이 1560.7 nm이고 스펙트럼의 폭은 약 1.1 nm이며, 연속 발진 반도체 레이저는 중심 파장이 1551 nm이고 스펙트럼의 폭은 약 6 MHz로 동작한다. 합주파수 생성을 효과적으로 수행하기 위해서 하나의 단일 모드 광섬유를 이용하여 PPLN 결정 내부에서 두 펌프 광원을 공간적으로 완전히 중첩하였다. 모드 잠금된 펄스 레이저와 좁은 선폭의 연속발진 반도체 레이저에 의해서 모드 잠금된 펄스 형태의 778 nm인 합주파수 생성을 스펙트럼과 시간적인 변화로 확인하였다. 본 연구 결과는 주파수 제어가 가능한 광주파수 빗(optical frequency comb)을 이용한 광주파수 측정 및 고분해 레이저 분광 연구 등 다양하게 응용될 수 있을 것으로 기대된다.

• 한국레이저가공학회지
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• 제12권4호
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• pp.6-11
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• 2009

The LDS(Laser Direct Structuring) process uses thermoplastic polymers with a additive compound that serves as plating seed after the activation by laser. It can realize industry requirement such as miniaturization of electrical component, design flexibility and reduction of production steps. The purpose of this study is to introduce LDS, and to investigate the fundamental mechanism. Also the characteristics of conductive patterns were investigated with respect to laser fluence and intensity. We have used a pulsed fiber laser (wavelength : 1064nm) and copper electroless plating to fabricate conductive patterns. The result showed that laser induced metal-organic complex was caused metalization by electroless copper plating, the critical laser fluence was $1.41\;J/cm^2$ at a scan speed of 1 m/s.

• 대한후두음성언어의학회지
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• 제27권1호
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• pp.51-53
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• 2016

Surgical fires require an ignition source, oxidizer, and fuel. The pulsed dye laser (PDL) has been shown to be effective in the treatment of hypertrophic scars and keloids in dermatology. With the increasing number of applications of $CO_2$, laser as ignition source has been associated with operating room fires in the otorhinolaryngologic field. There have been many case reports on PDL-induced fires in dermatology, but until now, there were no reports in the larynx. We describe a 57-year-old patient diagnosed with laryngeal hyperkeratosis treated by PDL-assisted laryngomicrosurgery. In this case, we experienced incidental PDL tip flaring during pulsed dye laser vaporization.

• Journal of Oral Medicine and Pain
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• 제24권4호
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• pp.397-410
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• 1999

In order to obtain the basic data concerning the optimal parameters in using Nd:YAG laser as a therapeutic modality to dentinal hypersensitivity, the author prepared 3 sections of sound dentin and 10 sections of sclerotic dentin with thickness of $0.5mm{\pm}0.1mm$ from human extracted teeth of anteriors and premolars, and applied the laser energy from a fiberoptic delivered, free running, pulsed Nd:YAG laser (wavelength 1064nm, pulse duration $120{\mu}sec$, fiber diameter $320{\mu}m$) to surfaces of sound and sclerotic dentin sections for 1 second with contact/unidirectional moving mode of the fiber under speed of 3mm~4mm/sec and parameters of 0.5W/10Hz, 1.0W/10Hz, 1.5W/10Hz, 2.0W/10Hz: $62J/cm^2$, $124J/cm^2$, $187J/cm^2$, $249J/cm^2$. The author comparatively evaluated the characteristics of ultrastructural changes on surfaces of sound and sclerotic dentin sections irradiated by the pulsed Nd:YAG laser using the scanning electron microscopy. A fairly ill-defined bordered surface of partially closed and melted dentinal tubules can be seen on the scanning electron microscopic feature of the sound dentin surface irradiated by the pulsed Nd:YAG laser with energy density of $62J/cm^2$. The physical modification of sound dentin surface extensively occurred depended on the increase of energy density from $62J/cm^2$ to $124J/cm^2$, $187J/cm^2$, $249J/cm^2$. While, a fairly well-defined bordered surface of partially closed and melted dentinal tubules with thickened peritubular dentin can be seen on the scanning electron microscopic feature of the sclerotic dentin surface irradiated by the pulsed Nd:YAG laser with energy density of $62J/cm^2$. The physical modification of sclerotic dentin surface of a fairly rough, shallow depression with many cracks, thickened peritubular dentin and structureless dentinal tubules extensively occurred depended on the increase of energy density from $62J/cm^2$ to $124J/cm^2$, $187J/cm^2$, $249J/cm^2$ compared to those of sound dentin surface irradiated by the pulsed Nd:YAG laser under the same parameters. Therefore, it is recommended that the pulsed Nd:YAG laser as a therapeutic modality to dentinal hypersensitivity should be applied with the less energy density than $62J/cm^2$ on the sound dentin surface, and its energy density on the partially sclerotic dentin surface should be lower than that on the sound dentin surface to preserve tooth from unnecessary excessive structural destruction.

• Journal of Oral Medicine and Pain
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• 제22권2호
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• pp.309-325
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• 1997

In order to set the lasing variables and evaluate, clinically, the therapeutic effects of a pulsed Nd:YAG laser on oral lesion, the author applied the laser energy from a fiberoptic delivered, free running, pulsed Nd:YAG laser (wavelength 1064nm, Pulse duration 120$\mu$sec, fiber diameter 200$\mu$m/320$\mu$m) to 22 cases of oral soft tissue lesions and 6 cases of oral hard tissue lesions. The obtained results were as follows : 1. The effective excision with contact mode and the effective hemostasis of accompanied bleeding with noncontact mode were occurred by lasing on oral soft tissue lesions with fiber diameter of 320$\mu$m under the variables of 2.0~4.0W and 20~50Hz which were controlled into high power/low pulses for excision, low power/high pulses for hemostasis, low power in granulation tissue and high power in fibrous tissue according to therapeutic goals and tissue conditions. 2. About 50% of decreasing effect on hypersensitivity was occurred by lasing with non-contact and contact mode on cervical abrasion which caused dentinal hypersensitivity with fiber diameter of 320$\mu$m under the variables of 0.7 - 1.0W and 10Hz which were applied 2~3 times with 1 week interval. 3. The effective sterilization of infected root canal and lesion of periapical abscess was occurred by lasing with contact and spiral modes on wall of root canal and periapical abscess with fiber diameter of 200$\mu$m of which the tip was placed about 1mm shorter than root canal length under the variables of 1.OW and 10Hz.

• Rapid Communication in Photoscience
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• 제4권3호
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• pp.50-53
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• 2015

$SnO_2$ thin films were deposited on fused silica substrate by pulsed laser deposition under transverse magnetic field. We have explored the effects of magnetic field and ablation laser wavelength on the optical properties of laser-induced plasma plume and structural characteristics of the deposited $SnO_2$ films. Optical emission from the plume was monitored using an optical fiber to examine the influence of magnetic field on the population of the excited neutral and ionic species and their decay with times after laser ablation. Also, we employed photoluminescence, x-ray diffraction, and UV-Vis absorption to characterize $SnO_2$ films.

• 한국생산제조학회지
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• 제22권4호
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• pp.643-651
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• 2013

This study applied a laser cleaning method (dry cleaning) that is used for cleaning semiconductor elements to dental implant cleaning. The lasers used in this study were pulsed fiber lasers with wavelengths of 1,064 and 532 nm. The peak output, energy per pulse, energy density per pulse, time of pulse experiment, and number of pulse experiments served as process variables for this study, and the variables were changed for each experiment. As a result, a laser with a wavelength of 532 nm showed much higher cleaning efficiency than its 1,064 nm counterpart. As the wavelength range decreased, the quantized energy increased and the reflection rate of the titanium used for the implant decreased; consequently, the energy absorption rate increased. Therefore, it is proposed that the energy density by wavelength has a greater influence on cleaning than does the output size.

• Journal of the Optical Society of Korea
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• 제19권2호
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• pp.130-135
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• 2015

Based on the extended nonlinear Schr$\ddot{o}$dinger equation, the influences of the filter effect on pulse splitting in a passively mode-locked erbium-doped fiber laser with positive dispersion cavity are investigated theoretically. Numerical results show that, as the bandwidth of the spectral filter decreases, the nonlinear chirp appended to the pulse increases under the combined action of the filter effect of the super-Gaussian spectral filter and the self-phase modulation effect. On further decreasing the bandwidth, the wave breaking of the pulse takes place. In addition, by varying the pump power of the laser or the profile of the spectral filter, the influences of the filter effect on pulse splitting also change accordingly.

• Nuclear Engineering and Technology
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• 제33권2호
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• pp.175-183
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• 2001

Various welding processes are now available for end cap closure of nuclear fuel element such as TG(Tungsten Inert Gas) welding, magnetic resistance welding and laser welding. Even though the resistance and TIG welding processes are widely used for manufacturing commercial fuel elements, they can not be recommended for the remote seal welding of a fuel element at a hot cell facility due to the complexity of electrode alignment, difficulity in the replacement of parts in the remote manner and a large heat input for a thin sheath. Therefore, the Nd:YAG laser system using optical fiber transmission was selected for Zircaloy-4 end cap welding inside hot cell. The laser welding apparatus was developed using a pulsed Nd:YAG laser of 500 watt average power with optical fiber transmission. The weldability of laser welding was satisfactory with respect to the microstructures and mechanical properties comparing with TIG and resistance welding. The optimum operation processes of laser welding and the optical fiber transmission system for hot cell operation in a remote manner have been developed The effects of irradiation on the properties of the laser apparatus were also being studied.