• Current Optics and Photonics
• /
• 제5권4호
• /
• pp.351-361
• /
• 2021

Speckle imaging is capable of dynamic data acquisition at high spatiotemporal resolution, and has played a vital role in the functional study of biological specimens. The presence of various optical scatterers within the tissue causes alteration of speckle contrast. Thus structures like blood vessels can be delineated and quantified. Although laser speckle imaging is frequently used, an optimization process to ensure the maximum speckle contrast has not been available. In this respect, we here report an experimental procedure to optimize speckle contrast via applying different combinations of varying polarization of the illuminating laser light and multiple analyzer angles. Specifically, samples were illuminated by the p-polarization, 45°-polarization, and s-polarization of the incident laser, and speckle images were recorded without and with the analyzer rotated from 0° to 180° (Δ = 30°). Following the baseline imaging of a solid diffuser and a fixed brain sample, laser speckle contrast imaging (LSCI) was successfully performed to visualize in vivo mouse-brain blood flow. For oblique laser illumination, the maximum contrast achieved with p-polarized and s-polarized light was perpendicular to the analyzer's axis. This study demonstrates the optimization process for maximizing the speckle contrast, which can improve blood-flow estimation in vivo.

• 한국기계가공학회지
• /
• 제20권6호
• /
• pp.59-69
• /
• 2021

Directed energy deposition (DED) is an additive manufacturing technology involving a focused high-power laser or electron beam propagating over the substrate, resulting in melt pool formation while simultaneously supplying metal powder to the melt pool area to deposit the material. DED is performed to repair and strengthen parts in various applications, as it can be easily integrate local area cladding and cross-material deposition. In this study, we characterize stainless steel 316 L parts fabricated via DED based on various deposition conditions and geometries to widen the application of DED. The deposition characteristics are investigated by varying the laser power and powder feed rate. Multilayer deposition with a laser power of 362 W and a powder feed rate of 6.61 g/min indicate a height closest to the design value while affording high surface quality. The microhardness of the specimen increases from the top to the bottom of the deposited area. Tensile tests of specimens with two different deposition directions indicate that horizontally long specimens with respect to a substrate demonstrate a higher ultimate tensile strength and yield strength than vertically long specimens with lower elongation.

• Journal of Electrical Engineering and Technology
• /
• 제11권2호
• /
• pp.508-518
• /
• 2016

In this paper, we propose a method combining an accelerometer with a cross structured light system to estimate the golf green slope. The cross-line laser provides two laser planes whose functions are computed with respect to the camera coordinate frame using a least square optimization. By capturing the projections of the cross-line laser on the golf slope in a static pose using a camera, two 3D curves’ functions are approximated as high order polynomials corresponding to the camera coordinate frame. Curves’ functions are then expressed in the world coordinate frame utilizing a rotation matrix that is estimated based on the accelerometer’s output. The curves provide some important information of the green such as the height and the slope’s angle. The curves estimation accuracy is verified via some experiments which use OptiTrack camera system as a ground-truth reference.

• KIEE International Transactions on Electrophysics and Applications
• /
• 제3C권2호
• /
• pp.43-47
• /
• 2003

Lead zirconate titanate (PZT) thin films were fabricated by the pulsed laser ablation deposition (PLAD) method onto Pt/Ti/SiO$_2$/Si substrates. Crystalline phases as well as preferred orientations in PZT films were investigated by X-ray diffraction analysis (XRD). The well-crystallized perovskite phase and the (101) preferred orientation were obtained by two-step annealing at the conditions of $650^{\circ}C$, 1 hour. It was found that the temperature for the pulsed laser ablated PZT films annealed via a two-step annealing process can be reduced 20$0^{\circ}C$ compared to that of the conventional three-step annealing temperature profile for enhancing the transformation of the perovskite phase. The remanent polarization and the coercive field of this film were about 20 $\mu$C/$\textrm{cm}^2$ and 46 kV/cm, while the dielectric constant and loss values measured at 1 KHz were approximately 860 and 0.04, respectively. The interesting phenomena of this film, such as vertical shift in hysteresis curve, are also discussed.

• 한국기계가공학회지
• /
• 제14권5호
• /
• pp.8-14
• /
• 2015

Heat treatment for car body molds is mainly a manual process performed by a worker. The performance of this process is affected by workers' skill level, and has limitation in maintaining uniform product quality. In this study, we developed a diode laser heat treatment robot system that implements an OLP type simulator to overcome the limitation of manual process, and to improve and stabilize the quality level. In addition, we verified the efficiency of the robot system and mechanism stability from the early stage through design verification and simulated analysis in the development stage. In addition, we carried out a field test to study the way to establish optimized D/B for diode laser heat treatment criteria for car body molds, such as heat treatment speed, interval, etc. via site experiment.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1778-1783
• /
• 2008

A compact and two-dimensional atomic force microscope (AFM) using an orthogonal sample scanner, a calibrated homodyne laser interferometer and a commercial AFM head was developed for use in the nanometrology field. The x and y position of the sample with respect to the tip are acquired by using the laser interferometer in the open-loop state, when each z data point of the AFM head is taken. The sample scanner which has a motion amplifying mechanism was designed to move a sample up to $100{\times}100{\mu}m^2$ in orthogonal way, which means less crosstalk between axes. Moreover, the rotational errors between axes are measured to ensure the accuracy of the calibrated AFM within the full scanning range. The conventional homodyne laser interferometer was used to measure the x and y displacements of the sample and compensated via an X-ray interferometer to reduce the nonlinearity of the optical interferometer. The repeatability of the calibrated AFM was measured to sub-nm within a few hundred nm scanning range.

• 한국광학회지
• /
• 제11권2호
• /
• pp.91-96
• /
• 2000

콜레스테릭 액정 플리머 박막을 이용한 새로운 개념의 광섬유 원편광 거울을 제작하고 그 특성을 분석하였다. 콜레스테릭 액정 거울의 광학적 특성을 보여주는 Jones Matrix를 유도하고 실험을 통하여 검증하였다. 제작된 광섬유 원편광 거울은 선형 광섬유 레이저 공진기에서 공간적 홀버닝을 제거하는데 사용 될 수 있으며, 광섬유 내에서의 비선형 편광 변화 효과를 이용한 모드록킹 동작을 얻을 수 있다. 실험을 통해 얻은 모드 록킹 된 레이저의 펄스 폭은 630fs로 측정 되었다.

• 한국자동차공학회논문집
• /
• 제5권6호
• /
• pp.167-174
• /
• 1997

The penetration depth and the size distribution of the droplets of fuel sprays are important in the operation of spark-ignition MPI engines. A fluorescence/scattering image technique for droplet sizing was applied to measure th edroplet size distribution in non-evaporating gasoline sprays. The fluorescence and scattering lights were imaged simultaneously by the two-dimensional visualization system composed of a laser sheet, a doubling prism, optical filters, and a CCD camera. Quantitative droplet size distributions were extracted from evaluating the ratio of the two light densities. The mean droplet size measured by the fluorescence/scattering technique was compared with the result obtained by the enlarged photographs of droplets. The fluorescence/scattering image technique also gives the useful information of the characteristics of droplet impingement in a inclined wall.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제53권11호
• /
• pp.583-588
• /
• 2004

We stabilized the frequency and power of a high voltage excited CW CO2 laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself. The photoacoustic signal is directly coupled from an radio frequency discharge chamber via a capacitor microphone into a detector and a lock-in stabilizer. The frequency stability is estimated to be better then 1.2×10/sup -7/ at the transition P(20) line. The stabilized output power variation was reduced to from 77 % to 3.3 %.

• Bulletin of the Korean Chemical Society
• /
• 제28권5호
• /
• pp.767-771
• /
• 2007

By adopting a time-resolved optical emission spectrometry, we have investigated the effects of transverse magnetic field on C2 and CN molecules produced by laser ablation of a graphite target in nitrogen atmosphere. We found that the spectroscopic temperatures of both species, obtained via simulation of the optical emission spectra, as well as their emission intensities from the electronically excited states increased significantly in the presence of a magnetic field. The cyclotron radii and frequencies for electrons and ions were estimated to explain the increase in the number of collisions in the laser-produced carbon plasma plume under a magnetic field.