• Korean Journal of Optics and Photonics
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• v.35 no.4
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• pp.150-156
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• 2024

One of the key factors in research regarding long-distance laser beam propagation, as in free-space optical communication or laser power transmission, is the transmission efficiency of the laser beam. As a way to improve efficiency, we perform extensive numerical simulations of the effect of modifying the laser beam's profile, especially replacing the fundamental Gaussian beam with a super-Gaussian beam. Numerical simulations of the transmitted power in the ideal diffraction-limited beam diameter determined by the optical system of the transmitter, after about 1-km propagation, reveal that the second-order super-Gaussian beam can yield superior performance to that of the fundamental Gaussian beam, in both single-channel and coherently combined multi-channel laser transmitters. The improvement of the transmission efficiency for a 1-km propagation distance when using a second-order super-Gaussian beam, in comparison with a fundamental Gaussian beam, is estimated at over 1.2% in the singlechannel laser transmitter, and over 4.2% and over 4.6% in coherently combined 3- and 7-channel laser transmitters, respectively. For a range of the propagation distance varying from 750 to 1,250 m, the improvement in transmission efficiency by use of the second-order super-Gaussian beam is estimated at over 1.2% in the single-channel laser transmitter, and over 4.1% and over 4.0% in the coherently combined 3- and 7-channel laser transmitters, respectively. These simulation results will pave the way for future advances in the generation of higher-order super-Gaussian beams and the development of long-distance optical energy-transfer technology.

• Korean Journal of Optics and Photonics
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• v.35 no.2
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• pp.49-60
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• 2024

We analyze the number of phase screens required for the simulation of a high-energy laser beam's propagation over an atmospheric channel. For high-energy lasers exceeding tens of kilowatts (kW) in power, the laser beam is mainly affected by atmospheric turbulence and thermal blooming. When using the split-step method to implement losses due to atmospheric absorption and scattering and distortion of the beam due to turbulence and thermal blooming, the number of phase screens is a critical factor in determining the accuracy and time required for the simulation. By comparing simulation results obtained using a large number of phase screens (e.g., 150 screens) under a wide range of atmospheric turbulence conditions, we provide new guidelines for the number of phase screens required for simulating the beam propagation of a high-power laser below 2.5×10⁶ W/m² (e.g., a 500-kW laser beam having a 50-cm diameter).

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.66-67
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• 2003

고출력 반도체 레이저는 EDFA의 펌핑소스, frequency-doubling 또는 tripling을 통한 자외선 혹은 가시광선의 생성, 의료 등 많은 응용분야를 가지고 있다. 특히 테이퍼드형 반도체 레이저는 대면적 레이저 다이오드와는 달리 단일모드를 만들어내는 리지영역과 이 빔이 회절없이 전파하며 고출력을 만들어내는 이득영역으로 되어 있어 고출력의 빔을 얻을 수 있을 뿐 아니라 고출력 발진시에도 횡적 안정성을 가지는 빔을 얻을 수가 있다. (중략)

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.242-242
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• 1999

상대론적 전자빔 발생장치(300kV, 40kA, 60ns)를 통하여 발생하는 전자빔은 진공 중에서 공간전하한계전류값을 갖게 되어 진행이 어렵다. 이런 전자빔의 전파특성을 향상시키기 위하여 여러 가지 방법들이 실험되어졌다. 본 실험실에서 수행한 실험은 전자빔의 진행해나가는 도파관 속에 국부적인 plasma channel을 형성시키고 이에 따른 전자빔의 전파율의 향상을 유도하였다. 이때 형성되는 높은 에너지의 이온빔을 관찰하고 이온 전류밀도에 따른 전자빔의 수송효율사이의 관계를 관찰하였다. 전류밀도의 증가는 여러 가지로 응용 될 수 있다. 자유전자레이저(Free Electron Laser)는 microwave로부터 가시광선 영역을 포함해 X-ray 영역까지의 coherent radiation을 발생시킬 수 있는 개념의 장치이다. 이 장치에서 전자빔의 전류밀도는 출력되는 전자기파의 power와 직접적으로 관계하여 고출력 microwave 발생장치를 구성할 수 있다. 이번 실험에서는 일정한 국부적으로 형성된 plasma에 따른 강렬한 상대론적 전자빔의 전파효율의 향상을 관찰하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.1
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• pp.1-12
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• 1997

The acousto-optical spectrometer as a new type backend of the receiver system for radio astronomical observations is manufactured for radio signal analysis. We studied on the effect of Acousto-Optic and Acousto-Optic devices and designed the optics system. We manufactured the optical mount and the CCD detector for deflected beam and interface card. This acousto-optical spectrometer consisted of a laser, optics, acousto-optic deflector, CCD detector and Interface card. This system use He-Ne laser as a light source and use optics to get parallel beam and to focus the deflected beam. Acousto-optic deflector converts IF signal to ultrasonic wave and deflect the laser beam according to the Bragg deflection. The ultra wide band acousto-optic deflector has 1 GHz bandwidth and a total of 2,048 channel Charge Coupled Device for signal detection. In this study, we discuss the theoretical description on the effect of Acousto-optics, the design of the optics, manufacture of optical mount, CCD detector, interface card and we presented the results of experiment. As a result of measurement, we have 1,000 channels bandwidth from CCD channels.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.310-311
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• 2000

Jo Bessel 빔은 무회절 빔으로서 빔이 전파해 가면서 강도 분포의 변화가 없는 빔이다.$^{[1]}$ 이 베셀빔을 구현하기 위해서는 무한대의 크기를 갖는 수렴렌즈를 사용하여야 하기 때문에 완벽한 베셀빔을 구현할 수는 없다. 그러나 원고리형 슬릿$^{[3]}$ , Axicon 및 Computer -Generated Hologram(CGH)을 사용하여 근사적인 Bessel 빔을 만들 수 있다. 본 실험에서는 Negative Branch Unstable Resonator(NBUR) 고리형 Nd:YAG 공진기와 scraper 출력경을 사용하여 원고리형 출력광을 얻으며, 이에 의한 Bessel 빔을 구현 하기 위한 이론적인 배경과 이의 전산시늉을 시도하고, 실험결과와의 비교, 분석하였다. (중략)

• Korean Journal of Optics and Photonics
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• v.35 no.4
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• pp.143-149
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• 2024

We analyze the effect of atmospheric fluctuation on laser beam propagation, using a single-phase screen model and a multi-phase screen model. When a laser beam (wavelength 1064 nm, radius 10 mm, collimated by 25.4 mm optics) propagates 3 km, atmospheric fluctuation with structure constant C_n² in the range of 10^-17 to 10^-14 is generated by the single- and multi-phase screen models. The results of short-term and long-term exposures are analyzed in terms of the beam profile, power in the bucket, and beam radius at the receiver plane. The power in the bucket and beam radius increase as the structure constant increases. When the structure constant is less than 2×10^-15, the results of the single- and multi-phase screen models are similar, within a difference of 1.5 %. However, when the structure constant is greater than 2×10^-15, the difference between the two models increases, and the multi-phase screen model is appropriate under this condition.

• Composites Research
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• v.29 no.5
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• pp.288-292
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• 2016

In this paper, a novel ultrasonic propagation imaging system, called a full-field pulse-echo ultrasonic propagation imaging (FF PE UPI) system is introduced. The system nondestructively inspected targets with two-axis translation stage. The coincident laser beams for ultrasonic sensing and generation are scanned and pulse-echo mode laser ultrasounds are captured. This procedure makes it possible to generate full-field ultrasound in through-the-thickness direction as large as the scan area. Structural inspection results in the form of full-field ultrasonic wave propagation videos are introduced, which are painted sandwich control surfaces. In addition, the inspection results of FF PE UPI system are compared with conventional ultrasonic testing methods such as waterjet and portable C-scan.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.74-85
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• 2024

As the limitations of conventional radio communications between satellites and the ground become apparent, various experiments are being conducted around the world to overcome them with space laser communication. In this study, we address the development of our own optical communications terminal (OCT) and optical ground station (OGS) and the experiments of free-space optical communication (FSOC) using them. Using a 30 mm-diameter OCT and a 250 mm-diameter portable OGS telescope, as well as commercial 10 Gbps SFP+ modules and media converters, we successfully transmitted and received 4K high-definition multimedia interface (HDMI) signals through 1,550 nm optical laser beam. The transmission and reception distances of the experiment were 3, 9, and 20 km, respectively, and the received signal strength at each distance was +6.1, -2.8, and -10.9 dBm, respectively. It was demonstrated that the 4K HDMI video lasted for over 10 minutes.

• Electronics and Telecommunications Trends
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• v.21 no.4 s.100
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• pp.118-128
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• 2006

테라헤르츠 대역(100GHz-10THz)은 광파와 전파의 경계 영역에 존재하며 기술적으로 뒤늦게 개발된 주파수 대역으로 테라헤르츠 대역을 개척하기 위해 최신의 레이저기술, 반도체 기술 및 고온초전도 기술을 사용하는 새로운 전자기파 기술로 발전하였다. 테라헤르츠 전자파 펄스는 펨토초 광펄스에 의한 초고속 광스위치(광전도 안테나),반도체 표면, 양자우물 구조 등의 여기(excitation)에 의해 발생하고, 두 가지 연속파(CW) 레이저 빔을 혼합하면 주파수 가변의 테라헤르츠 전자파가 발생한다. 본 논문에서는 이와 같은 THz 전자파 펄스의 발생 및 검출과 THz 응용분야에 대해 기술하고자한다.