• 열처리공학회지
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• 제13권5호
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• pp.318-323
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• 2000

The planarization of rough polycrystalline diamond films synthesized by DC arc discharge plasma jet CVD (chemical vapor deposition) was attempted using KrF excimer laser pulses. The effects of laser incidence angle and reaction gases (ozone and oxygen) on etching rate of diamond were studied. The temperature change of diamond and graphite with different laser fluences was calculated by computer simulation to explain the etching behavior of diamond films. The threshold energy density from the experiment for etching of pure crystalline diamond was about $1.7J/cm^2$ and fairly matched the simulation value. Preferential etching of a particular crystallographic plane was observed through scanning electron microscopy. The etching rate of diamond with ozone was lower than that with oxygen. When the angle of incidence was $80^{\circ}$ to the diamond surface normal, the peak-to-valley surface roughness was Significantly reduced from $20{\mu}m$ to $0.5{\mu}m$.

• Journal of Photoscience
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• 제6권3호
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• pp.103-108
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• 1999

We present recent results on ablation mechanism, single-pulse laser micropatterning , pulsed-laser deposition(PLD) and particulates formation accompanying laser ablation, with special emplasis on polymers, in particular polymide, (PI), and polytetrafluoroethylene, (PTFE). Ablation of polymers is described on the basis of photothermal bond breaking within the bulk material. Here, we assume a first order chemical reaction, which can be described by an Arrhenius law. Ablation starts when the density of broken bonds at the surface reaches a certain critical value. Single-pulse laser ablation of polyimide shows a clear-length dependence of the threshold fluence. This experimental result strongly supports a thermal ablation model. We discuss the various possibilities and drawbacks of PLD and describe the morphology, physical properties and applications of PTFE films.

• Current Optics and Photonics
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• 제6권4호
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• pp.381-391
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• 2022

Two-photon-polymerization additive-manufacturing systems feature high resolution and precision. However, there are few reports on specific methods and possible problems concerning the use of small lasers to independently build such platforms. In this paper, a femtosecond-laser two-photon-polymerization additive-manufacturing system containing an optical unit, control unit, monitoring unit, and testing unit is built using a miniature femtosecond laser, with a detailed building process and corresponding control software that is developed independently. This system has integrated functions of light-spot detection, interface searching, micro-/nanomanufacturing, and performance testing. In addition, possible problems in the processes of platform establishment, resin preparation, and actual polymerization for two-photon-polymerization additive manufacturing are explained specifically, and the causes of these problems analyzed. Moreover, the impacts of different power levels and scanning speeds on the degree of polymerization are compared, and the influence of the magnification of the object lens on the linewidth is analyzed in detail. A qualitative analysis model is established, and the concepts of the threshold broadening and focus narrowing effects are proposed, with their influences and cooperative relation discussed. Besides, a linear structure with micrometer accuracy is manufactured at the millimeter scale.

• 한국광학회지
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• 제15권2호
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• pp.171-176
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• 2004

광 편향기가 집적된 레이저 다이오드를 제작하고 편향기 주입전류에 따른 레이저 다이오드의 특성 변화 및 출력광의 편향을 조사하였다. 레이저 다이오드와 집적된 수동 도파로의 상부 클래드 층의 일부분에 광 편향기를 집적하고, 편향기의 전류 주입에 따른 굴절률 변화를 유도하여 출력광의 편향이 발생하도록 하였다. 편향기의 전류 주입에 따른 출력광의 특성변화를 조사하기 위하여 편향기 주입 전류에 따른 레이저 다이오드의 문턱 전류(threshold current), 발진 효율(slope efficiency) 및 출력광 스펙트럼을 측정하였다. 측정 결과, 편향기 전류의 증가에 따라 출력광의 문턱 전류는 증가하고, 발진 효율은 감소하는 경향을 나타내었으나 출력광의 스펙트럼에는 영향을 주지 않는 특성을 나타내었다. 또한, 이론적 계산을 통해 광 편향기를 지나는 광이 편향됨을 확인하고, 편향기 집적 레이저 다이오드에서 출력되는 광의 far-field pattern을 측정하여 편향기 주입 전류에 따른 출력광의 편향을 실험적으로 확인하였다. 제작된 광 편향기 집적 레이저 다이오드에서 15 ㎃의 광 편향기 주입 전류 변화에 대해서 1.9$^{\circ}$의 편향각 변화를 측정 할 수 있었다.

• 문화기술의 융합
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• 제6권4호
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• pp.727-732
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• 2020

본 연구에서는 1.55um의 파장을 갖는 DFB 레이저에서 굴절률 격자와 이득 격자가 동시에 존재할 때, 오른쪽 거울 면에 반사가 일어나지 않도록 유전막 코팅을 하여 𝜌_r=0 이 되도록 하였다. δL > 0인 경우일 때, 문턱에서 발진 모드에 대하여, 발진 이득과 종 방향으로의 발진 모드의 빔 분포와 방사전력비 P_l/P_r를 𝜌_l의 위상=π인 경우와 𝜌_l의 위상=π/2인 경우에 대하여 비교했다. 𝜌_l의 위상=π인 경우, 낮은 문턱 전류와 높은 주파수 안정성을 얻기 위해서는, κL이 8보다 커야 한다. 𝜌_l의 위상=π/2인 경우, κL = 4보다 커지면서 𝜌_l의 위상=π인 경우보다 발진 이득이 낮아지기 시작함을 볼 수 있고, 발진 모드의 문턱 전류를 낮추고 주파수 안정성을 높이기 위해서는, κL이 8보다 커야한다.

• 한국멀티미디어학회논문지
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• 제21권2호
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• pp.181-187
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• 2018

Line-laser beams are used for depth measurement of welding beads along the circumference of a pipe. For this, first we project a line-laser beam on an rotating pipe and take a sequence of images of the beam projected on the pipe using a CCD camera. Second, the projected line laser beam in each image is detected, converted into a thin curve. Finally measure the distance between the thinned curve and an imaginary line. When a line-laser beam is projected to a rough metal surface such as arc welding beads, the beam is severely scattered. This severe scattering makes the thinned curve perturbed. In this paper, we propose a thinning method robust against scattering of line lasers. First, we extract a projected line laser beam region using an adaptive threshold. Second, we model a thinned curve with a spline curve with control points. Next, we adjust the control points to fit the curve to the projected line-laser beam. Finally, we take a weighted mean of thin curves on a sequence of image frames. Experiments shows that the proposed thinning method results in a thinning curve, which is smooth and fit to the projected line-laser beam with small error.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 디스플레이 광소자 분야
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• pp.129-132
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• 2000

The PDP(Plasma Display Panel) barrier rib material on the glass substrate was patterned for fabrication of the PDP cell using Nd:YAG laser(1064 nm) which can generate the second(532 nm) and forth(266 nm) harmonic wave by HGM(harmonic generation modules). At a scan speed of 20 ${\mu}m/s$ with the second harmonic wave(532 nm) of Nd:YAG laser, the etching threshold laser fluence of the PDP material was 6.5 $mJ/cm^2$ and a sample(thickness = 180 ${\mu}m$) on the glass substrate was removed clearly at a laser fluence of 19.5 $mJ/cm^2$. In order to increase the throughput of the fabrication we divided a single-beam into multi-beams by using a metal mask between the sample and the focusing lens. As a result, 10 lines of PDP cell were formed by one laser beam scanning at a scan speed of 200 ${\mu}m/s$ and a laser fluence of 2.86 $J/cm^2$.

• ETRI Journal
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• 제32권2호
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• pp.339-341
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• 2010

The fundamental transverse mode lasing of a hybrid laser diode is a prerequisite for efficient coupling to a single-mode silicon waveguide, which is necessary for a wavelength-division multiplexing silicon interconnection. We investigate the lasing mode profile for a hybrid laser diode consisting of silicon slab and InP/InGaAsP deep ridge waveguides. When the thickness of the top silicon is 220 nm, the fundamental transverse mode is lasing in spite of the wide waveguide width of $3.7{\mu}m$. The threshold current is 40 mA, and the maximum output power is 5 mW under CW current operation. In the case of a thick top silicon layer (1 ${\mu}m$), the higher modes are lasing. There is no significant difference in the thermal resistance of the two devices.

• 한국광학회:학술대회논문집
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• 한국광학회 1990년도 제5회 파동 및 레이저 학술발표회 5th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.59-63
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• 1990

Two-stage TEA(transversely excited atmospheric pressure) CO2 laser amplifier system, Amp I and Amp II are consturcted and their amplification characteristics are investigated theoretically and experimentally. Multiple-wire corona preionization method is used for uniform discharge in laser oscillator and amplifiers. At optimumm gas ratio, CO2 : N2 : He = 1 : 1 : 3, output pulse energy of the oscillator is 0.4J and finally two-stage amplification gives 1.5J output energy which is larger than pumping threshold of para-H2 Raman laser. The rate equations of the amplifiers are solved numerically, and the results are compared with the experimental results. In conclusion, the small signal gain cocfficient of AMP I is 0.025/cm and that of AMP II is 0.02/cm.

• Journal of Oral Medicine and Pain
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• 제21권1호
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• pp.25-36
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• 1996

To investigate the effect of low level laser therapy, the author selected 37 dental students with tender points in both masseters and trapeziuses, also measured maximum comportable opening(MCO), Numerical analog scale(NAS) and pressure pain threshold (PPT). 20 subjects were assigned randomly and were treated with GaAlAs diode laser after ultrasound. The other 17 subjects were treated with ultrasound and laser without irradiation. All the subjects were treated after 2 and 4 day respectively and were examined again after 6 days. And the obtained results were as follows : 1. The MCO of irradiated group increased more significantly after treatment than non-irradiated group. 2. The NAS of irradiated group decreased more significantly after treatment than non-irradiated group. 3. The PPT or irradiated group increased more significantly after treatment than non-irradiated group.