• Korean Journal of Optics and Photonics
• /
• v.20 no.1
• /
• pp.34-40
• /
• 2009

In-situ pulse laser (Nd-YAG, 2nd harmonics 532 nm) annealing used in physical vapor deposition of $MgF_2$, $SiO_2$ and ZnS thin films was shown to be effective in improving their surface roughness properties. Total integrated scattering (TIS) measurements of $MgF_2$ and $SiO_2$ samples deposited on glass substrates revealed that the laser irradiation of films at an energy of approximately $140\;mJ/cm^2$ at 532 nm with a repetition frequency of 10 Hz and pulse duration of 5 ns during the deposition resulted in total scatterings that were minimum. But in case of the ZnS samples, measurements revealed minimum total scattering at a laser energy of approximately $62\;mJ/cm^2$. Atomic Force Microscopy (AFM) has been used to evaluate the effect of pulse laser annealing on the surface roughness for thin film samples. The results were similar to the TIS measurements, indicating that surface roughness was decreased when the irradiated annealing pulse laser energy increased. But it also increased when the irradiated annealing pulse laser energy was over some limit that depended on the materials.

• Korean Journal of Optics and Photonics
• /
• v.10 no.5
• /
• pp.357-363
• /
• 1999

A frequency domain spectroscopic system was constructed to investigate the optical properties of multiple scattering media. The alternating current (AC) and phase lag components of backscattered light were measured by using the heterodyne detection method. Absorption and transport scattering coefficients were computed from the values based on diffusion theory. Predictions showed excellent matches in comparison with actual values of absorption and scattering. Predictable ranges of the optical coefficients were analyzed in terms of the distance between light source and detector, and modulation frequencies. A proposed compact experimental set-up using laser diodes can be utilized to estimate non-invasively the optical properties of multiple scattering media such as biological tissues.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.13 no.4
• /
• pp.36-44
• /
• 2009

Spray cross-section was measured by the Optical Line Patternator (OLP) and Optical Tomography at high ambient pressure. The laser line beam passed through the spray region, then Mie scattered signal and transmitted light were captured. The measured signal was processed to obtain a distribution of attenuation coefficient in spray cross-section. Beer-Lambert's law and mathematical reconstruction methods were used to reconstruct the distribution of attenuation coefficient. Spray became dense at high pressure and attenuation of scattered signal occurred seriously. OLP method, which uses Mie scattered signal, showed limit in compensating attenuation problem in dense spray region. Optical tomography reconstructed spray cross-section well, from transmission rate of light penetrating spray region.

• Korean Journal of Optics and Photonics
• /
• v.32 no.3
• /
• pp.120-125
• /
• 2021

We have developed a linearly polarized high-power Yb-doped fiber laser in the master oscillator power amplifier (MOPA) scheme for efficient spectral beam combining. We modulated the phase of the seed laser by pseudo-random binary sequence (PRBS), with the bit length optimized to suppress stimulated Brillouin scattering (SBS), and subsequently amplified seed power in a 3-stage amplifier system. We have constructed by coiling the polarization-maintaining (PM) Yb-doped fiber, with core and cladding diameters of 20 ㎛ and 400 ㎛ respectively, to a diameter of 9-12 cm for suppression of the mode instability (MI). Finally, we obtained an output power of 1.004 kW with a slope efficiency of 83.7% in the main amplification stage. The beam quality factor M² and the polarization extinction ratio (PER) were measured to be 1.12 and 21.5 dB respectively. Furthermore, the peak-intensity difference between the Rayleigh signal and SBS signal was observed to be 2.36 dB in the backward spectra, indicating that SBS is successfully suppressed. In addition, it can be expected that the MI does not occur because not only there is no decrease in slope efficiency, but also the beam quality for each amplified output is maintained.

• Journal of the korean Society of Automotive Engineers
• /
• v.7 no.1
• /
• pp.12-17
• /
• 1985

주위기체와 다른 기체를 간헐적으로 또는 단발로 분사한 경우, 분류내의 분사체의 농도는 시간에 따라 급격히 변화한다. 수ms인 전자식기체 채취밸브를 이용해서 기체를 채취하고, 가스마토그 라프 등에 의해 가스분석을 행하는 방법이 있고 주로 피스톤식 내연기관의 연소실내 농도의 측 정에 이용되고 있다. 이 방법은 밸브 열립시간을 단축시켜도 약 1ms가 한도이고 시간분해능력도 1ms정도가 최단시간이다. 또 동일한 장소에서 농도의 시간경과를 얻는 데에는 각각의 시간에 대해서 기체의 채취와 분석을 행하지 않으면 안되어 실제시간의 농도측정이 불가능하다는 결점이 있다. 최근 레이저 응용기술의 진보에 의해 라만산란, 레리산란, CARS법 등의 농도순간측정이 가능해지고 있고, 점차 현실화되어가고 있다. 이들의 방법은 국소의 순간농도뿐만 아니라 온도의 동시측정도 가능하게 하는 특징을 갖고있다. 그러나 레이저에 의한 측정장치는 현시정에서는 아직 가격이 고가이고 광학계의 설치 등, 실험상의 조작이 복잡한 것 등의 결점을 갖고 있다. 본 고에서는 최근 진전이 현저하고 실용화에 대한 확신을 갖고 있는 열선농도Probe에 의한 순간농 도의 측정방법을 소개하고자 한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2012.05a
• /
• pp.568-570
• /
• 2012

The algorithm to distinguish cloud from aerosols in the measurements of Laser Radar is developed. This method use the difference of slope between return signals of cloud and aerosols. The parameters achieved from the algorithm are altitude of cloud top, cloud base, and boundary layer.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.7
• /
• pp.58-64
• /
• 2009

In this paper, an inspection mechanism based on laser scattering has been developed for the surface evaluation of infrared cut-off filters, and optimum conditions of laser scattering are determined using the design of experiment. First of all, attributes and influence factors of laser scattering are investigated and then a laser scattering inspection mechanism is newly designed based on analyses of laser scattering parameters. Also, Taguchi method, one of experimental designs, is used for the optimum condition selection of laser scattering parameters and the optimum condition is determined in order to maximize the detection capability of surface defects. Experiments show that the proposed method is useful in a consistent and effective defect detection and can be applied to surface evaluation processes in manufacturing.

• Journal of the Korean Society for Precision Engineering
• /
• v.24 no.11
• /
• pp.76-83
• /
• 2007

The dark-field laser scattering system has been developed to inspect surface defects in infrared cut-off filters and then laser scattering characteristics against the defects are investigated. The qualitative analysis for the reliable and accurate detection performance is described through the correlation between incident angles of a laser and viewing ones of a camera. In this paper, reliable and important information with laser scattering is given for the surface defect inspection of IR filters. Its performance has been verified through various experiments.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.7 no.3
• /
• pp.579-583
• /
• 2012

We have designed the small particle detection system. The scatteing effect of light was used to detect small particle. The fabricated system consisted of laser diode, lens, pin hole, and photo detector. The aperture, lens, and photo detector were optimized to improve the performance of detection system. The fabricated detection system detected the scattered light by small particle entering into detection system and its response time was fast.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.5
• /
• pp.606-613
• /
• 2011

In this paper, patterns of laser scattering and detection of micro defects have been investigated based on Rayleigh criterion for silicon wafer in solar cell. Also, a new laser scattering mechanism is designed using characteristics of light scattering against silicon wafer surfaces. Its parameters are to be optimally selected to obtain effective and featured patterns of laser scattering. The optimal parametric ranges of laser scattering are determined using the mean intensity of laser scattering. Scattering patterns of micro defects are investigated at the extracted parameter region. Among a lot of pattern features, both maximum connected area and number of connected component in patterns of laser scattering are regarded as the important information for detecting micro defects. Their usefulness is verified in the experiment.