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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Optical Society of Korea
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Optical Society of Korea
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Volume & Issues
Volume 13, Issue 4 - Dec 2009
Volume 13, Issue 3 - Sep 2009
Volume 13, Issue 2 - Jun 2009
Volume 13, Issue 1 - Mar 2009
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International and Asian Networks on Intense Laser Science
Kato, Yoshiaki ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 2~7
DOI : 10.3807/JOSK.2009.13.1.002
This paper reviews evolution of the research networks on intense laser science under international and Asian frameworks during 2000 to 2008. The OECD Global Science Forum Steering Committee on Compact, High-Intensity Short-Pulse Lasers led to the establishment of the International Union of Pure and Applied Physics (IUPAP) Working Group: International Committee on Ultrahigh Intensity Lasers (ICUIL) and the Asian Intense Laser Network (AILN) in 2004. Through various activities under AILN such as the Asian Symposium on Intense Laser Science (ASILS), the Asian Summer School on Laser Plasma Acceleration and Radiation, and the High-Order Harmonics Workshops, closer relations are being formed among the scientists and also among the young generations working in intense laser science in the Asian regions.
Laser Acceleration of Electron Beams to the GeV-class Energies in Gas Jets
Hafz, Nasr A.M. ; Jeong, Tae-Moon ; Lee, Seong-Ku ; Choi, Il-Woo ; Pae, Ki-Hong ; Kulagin, Victor V. ; Sung, Jae-Hee ; Yu, Tae-Jun ; Cary, John R. ; Ko, Do-Kyeong ; Lee, Jong-Min ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 8~14
DOI : 10.3807/JOSK.2009.13.1.008
In a laser-plasma wakefield accelerator, the ponderomotive force of an ultrashort high intensity laser pulse excites a longitudinal wave or plasma bubble in a way similar to the excitation of a wake wave behind a boat as it propagates on the water surface. Electric fields inside the plasma bubble can be several orders of magnitude higher than those available in conventional RF-based particle accelerator facilities which are limited by material breakdown. Therefore, if an electron bunch is properly phase-locked with the bubble's acceleration field, it can gain relativistic energies within an extremely short distance. Here, in the bubble regime we show the generation of stable and reproducible sub GeV, and GeV-class electron beams. Supported by three-dimensional particle-in-cell simulations, our experimental results show the highest acceleration gradients produced so far. Simulations suggested that the plasma bubble elongation should be minimized in order to achieve higher electron beam energies.
High-harmonic Generation from Solid Surface Using an Oscillating Mirror Model and Plasma Mirror System for High Contrast Laser Pulse
Kim, I-Jong ; Choi, Il-Woo ; Janulewicz, Karol Adam ; Lee, Jong-Min ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 15~21
DOI : 10.3807/JOSK.2009.13.1.015
High-order harmonic generation from a solid surface affected by the contrast of a laser pulse was studied using an oscillating mirror model. High-order harmonics generated from solid surfaces have unusual properties such as spectral redshift, and an intensity difference between even- and odd-order harmonics which is not reported for high-order harmonics generated by a gas medium. We confirmed that high-order harmonics from solid surfaces have selectivity of polarization as well as cut-off extension and the enhancement of conversion efficiency proportional to laser intensity. And the principle of operation and the characteristics of a plasma mirror system developed for achieving high contrast laser pulses to pursue the experimental realization of high-harmonic generation from solid surfaces are reported. Energy fluence on the plasma mirrors is tunable between
and around 1000 shots are available before the plasma mirrors require replacement.
Improvement of Proton Beam Quality from the High-intensity Short Pulse Laser Interaction with a Micro-structured Target
Seo, Ju-Tae ; Yoo, Seung-Hoon ; Pae, Ki-Hong ; Hahn, Sang-June ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 22~27
DOI : 10.3807/JOSK.2009.13.1.022
Target design study to improve the quality of an accelerated proton beam from the interaction of a high-intensity short pulse laser with an overdense plasma slab has been accomplished by using a two-dimensional, fully electromagnetic and relativistic particle-in-cell (PIC) simulation. The target consists of a thin core part and a thick peripheral part of equivalent plasma densities, while the ratio of the radius of the core part to the laser spot size, and the position of the peripheral part relative to the fixed core part were varied. The positive effects of this core-peripheral target structure could be expected from the knowledge of the typical target normal sheath acceleration (TNSA) mechanism in a laser-plasma interaction, and were apparently evidenced from the comparison with the case of a conventional simple planar target and the case of the transversal size reduction of the simple planar target. Improvements of the beam qualities including the collimation, the forward directionality, and the beam divergence were verified by detailed analysis of relativistic momentum, angular directionality, and the spatial density map of the accelerated protons.
Radiography with Low Energy Protons Generated from Ultraintense Laser-plasma Interactions
Choi, Chang-Il ; Lee, Dong-Hoon ; Kang, Byoung-Hwi ; Kim, Yong-Kyun ; Choi, Il-Woo ; Sung, Jae-Hee ; Kim, Chul-Min ; Kim, I-Jong ; Yu, Tae-Jun ; Lee, Seong-Ku ; Pae, Ki-Hong ; Hafz, Nasr ; Jeong, Tae-Moon ; Ko, Do-Kyeong ; Lee, Jong-Min ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 28~32
DOI : 10.3807/JOSK.2009.13.1.028
In order to obtain high quality images of thin objects, we performed an experiment of proton radiography by using low energy protons generated from the interaction of an ultrashort ultraintense laser with solid targets. The protons were produced from a thin polyimide target irradiated by the laser pulse, and their maximum energy was estimated at up to 1.8 MeV. A CR-39 nuclear track detector was used as a proton radiography screen. The proton images were obtained by using an optical microscope and the spatial resolution was evaluated by a Modulation Transfer Function (MTF). We have achieved about
spatial resolution of images. The obtained spatial resolution shows about
times better value than the conventional X-ray radiography for inspection or non-destructive test (NDT) purpose.
Microstructuring of Optical Fibers Using a Femtosecond Laser
Sohn, Ik-Bu ; Kim, Young-Seop ; Noh, Young-Chul ; Ryu, Jin-Chang ; Kim, Jin-Tae ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 33~36
DOI : 10.3807/JOSK.2009.13.1.033
Laser ablation with femtosecond lasers is highly promising for microfabrication of materials. Also, the high peak power of femtosecond lasers could induce a multiphoton absorption to ablate transparent materials. Similar results have also been were obtained in the case of optical fibers. In this paper, we present our experimental results of femtosecond laser microstructuring of optical fiber and its applications to microelectronic components and fiber optic devices. Finally, we directly produced micro holes with femtosecond laser pulses in a single step by moving an optical fiber in a preprogrammed structure. When water was introduced into a hole drilled from the bottom surface of the optical fiber, the effects of blocking and redeposition of ablated material were greatly reduced and the aspect ratio of the depth of the hole was increased. We have presented circular and rectangular-shaped holes in optical fiber.
Development of Laser-driven Proton Source Toward Its Applications
Sagisaka, Akito ; Daido, Hiroyuki ; Pirozhkov, Alexander S. ; Yogo, Akifumi ; Ogura, Koichi ; Orimo, Satoshi ; Ma, Jinglong ; Mori, Michiaki ; Nishiuchi, Mamiko ; Bulanov, Sergei V. ; Esirkepov, Timur Zh. ; Oishi, Yuji ; Nayuki, Takuya ; Fujii, Takashi ; Nemoto, Koshichi ; Nagatomo, Hideo ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 37~41
DOI : 10.3807/JOSK.2009.13.1.037
We observe the proton signals produced by laser interaction with thin-foil targets of polyimide and of copper. We change the thickness of the polyimide target to
. High-energy protons with the maximum energy of
thick polyimide are observed. This proton beam with the maximum energy of multi-MeV has various applications such as a proton shadowgraphy.
The Effect of Density Gradient on the Self-modulated Laser Wakefield Acceleration with Relativistic and Kinetic Effects
Yoo, Seung-Hoon ; Kim, Jae-Hoon ; Kim, Jong-Uk ; Seo, Ju-Tae ; Hahn, Sang-June ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 42~47
DOI : 10.3807/JOSK.2009.13.1.042
The propagation of an intense laser pulse through an upward density-gradient plasma in a self-modulated laser wakefield acceleration (SM-LWFA) is investigated by using particle-in-cell (PIC) simulations. In the fully relativistic and kinetic PIC simulations, the relativistic and kinetic effects including Landau damping enhance the electron dephasing. This electron dephasing is the most important factor for limiting the energy of accelerated electrons. However, the electron dephasing, which is enhanced by relativistic and kinetic effects in the homogeneous plasma, can be forestalled through the detuning process arising from the longitudinal density gradient. Simulation results show that the detuning process can effectively maintain the coherence of the laser wake wave in the spatiotemporal wakefield pattern, hence considerable energy enhancement is achievable. The spatiotemporal profiles are analyzed for the detailed study on the relativistic and kinetic effects. In this paper, the optimum slope of the density gradient for increasing electron energy is presented for various laser intensities.
Effects of the Micro-hole Target Structures on the Laser-driven Energetic Proton Generation
Pae, Ki-Hong ; Choi, Il-Woo ; Hahn, Sang-June ; Lee, Jong-Min ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 48~52
DOI : 10.3807/JOSK.2009.13.1.048
Micro-hole targets are studied to generate energetic protons from laser-thin foil targets by using 2-dimensional particle-in-cell simulations. By using a small hole, the maximum energy of the accelerated proton is increased to 4 times higher than that from a simple planar target. The main proton acceleration mechanism of the hole-targets is the electrostatic field created between the fast electrons accelerated by the laser pulse ponderomotive force combined with the vacuum heating and the target rear surface. But in this case, the proton angular distribution shows double-peak shape, which means poor collimation and low current density. By using a small cone-shaped hole, the maximum proton energy is increased 3 times higher than that from a simple planar target. Furthermore, the angular distribution of the accelerated protons shows good collimation.
Design of a Femtosecond Ti:sapphire Laser for Generation and Temporal Optimization of 0.5-PW Laser Pulses at a 0.1-Hz Repetition Rate
Sung, Jae-Hee ; Yu, Tae-Jun ; Lee, Seong-Ku ; Jeong, Tae-Moon ; Choi, Il-Woo ; Ko, Do-Kyeong ; Lee, Jong-Min ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 53~59
DOI : 10.3807/JOSK.2009.13.1.053
A chirped-pulse amplification Ti:sapphire laser system has been designed using a 10-Hz 100-TW Ti:sapphire laser to generate 0.1-Hz 0.5-PW laser pulses and optimize their temporal qualities such as temporal contrast and pulse duration. A high-energy booster amplifier to be added is expected to produce an energy above 30 J through the parasitic lasing suppression and the efficient amplification. To improve the temporal contrast of the laser pulses, a high-contrast 1-kHz amplifier system is used as a front-end. A grating stretcher which makes the laser pulse have 1-ns duration is used to prevent optical damages due to high pulse energy during amplification. A grating compressor has been designed with group delay analysis to obtain the recompressed pulse duration close to the transform-limited pulse duration. The final laser pulses are expected to have energy above 20 J and duration below 40 fs.
High-resolution Spectroscopy of the Nickel-like Molybdenum X-ray Laser Toward the Generation of Circularly Polarized X-ray Laser
Hasegawa, Noboru ; Sasaki, Akira ; Yamatani, Hiroshi ; Kishimoto, Maki ; Tanaka, Momoko ; Ochi, Yoshihiro ; Nishikino, Masaharu ; Kunieda, Yuichi ; Kawachi, Tetsuya ; Yoneda, Hitoki ; Iwamae, Atsushi ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 60~64
DOI : 10.3807/JOSK.2009.13.1.060
We attempted the first measurement of the spectral width of the nickel-like molybdenum x-ray laser (
) by use of a high-resolution spectrometer in order to determine the strength of the magnetic field required for the generation of a circularly polarized x-ray laser. The spectral width was measured to be
under the substantial lasing condition. The magnetic field required for the generation of a circularly polarized x-ray laser was 40 T. The splitting of the x-ray laser line was clearly obtained under 15 T external magnetic field. The strength of the magnetic field estimated from the splitting of the x-ray laser line was large compared with the external magnetic field. It implies that there might be an alternative mechanism for enhancement of the magnetic field in the gain medium plasma.
Parametric Studies of Pulsed Laser Deposition of Indium Tin Oxide and Ultra-thin Diamond-like Carbon for Organic Light-emitting Devices
Tou, Teck-Yong ; Yong, Thian-Khok ; Yap, Seong-Shan ; Yang, Ren-Bin ; Siew, Wee-Ong ; Yow, Ho-Kwang ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 65~74
DOI : 10.3807/JOSK.2009.13.1.065
Device quality indium tin oxide (ITO) films are deposited on glass substrates and ultra-thin diamond-like carbon films are deposited as a buffer layer on ITO by a pulsed Nd:YAG laser at 355 nm and 532 nm wavelength. ITO films deposited at room temperature are largely amorphous although their optical transmittances in the visible range are > 90%. The resistivity of their amorphous ITO films is too high to enable an efficient organic light-emitting device (OLED), in contrast to that deposited by a KrF laser. Substrate heating at
with laser wavelength of 355 nm, the ITO film resistivity decreases by almost an order of magnitude to
while its optical transmittance is maintained at > 90%. The thermally induced crystallization of ITO has a preferred <111> directional orientation texture which largely accounts for the lowering of film resistivity. The background gas and deposition distance, that between the ITO target and the glass substrate, influence the thin-film microstructures. The optical and electrical properties are compared to published results using other nanosecond lasers and other fluence, as well as the use of ultra fast lasers. Molecularly doped, single-layer OLEDs of ITO/(PVK+TPD+
)/Al which are fabricated using pulsed-laser deposited ITO samples are compared to those fabricated using the commercial ITO. Effects such as surface texture and roughness of ITO and the insertion of DLC as a buffer layer into ITO/DLC/(PVK+TPD+
)/Al devices are investigated. The effects of DLC-on-ITO on OLED improvement such as better turn-on voltage and brightness are explained by a possible reduction of energy barrier to the hole injection from ITO into the light-emitting layer.
Four-beam Interference Optical System for Laser Micro- structuring Using Picosecond Laser
Noh, Ji-Whan ; Lee, Jae-Hoon ; Shin, Dong-Sig ; Sohn, Hyon-Kee ; Suh, Jeong ; Oh, Jeong-Seok ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 75~79
DOI : 10.3807/JOSK.2009.13.1.075
A four beam interference optical system for laser micro structuring using a pulse laser was demonstrated. The four beam interference optical system using a pulse laser(picosecond laser) can fabricate micro structure on mold material(NAK80) directly. Micro structure on the polymer can be reproduced economically by injection molding of the micro structure on the mold material. The four beam interference optical system was composed by the DOE(Diffractive Optical Element) and two lenses. The laser intensity distribution of four beam interference was explained by an interference optics point of view and by the image optics point of view. We revealed that both views showed the same result. The laser power distribution of a
peak pattern was made by the four beam interference optical system and measured by the objective lens and CCD. A
pitch dot pattern on the mold material was fabricated and measured by SEM(Scanning Electron Microscopy).
Efficient keV X-ray Generation from Irradiation of in-situ Produced Silver Clusters by Ti:sapphire Laser Pulses
Chakravarty, U. ; Naik, P.A. ; Kumbhare, S.R. ; Gupta, P.D. ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 80~85
DOI : 10.3807/JOSK.2009.13.1.080
An experimental study of energy absorption and x-ray emission from ultrashort laser pulse irradiation of in-situ produced solid clusters has been performed. Silver clusters produced by a 30 mJ, 300 ps laser pulse were irradiated up to an intensity of
by a 70 mJ, 45 fs compressed laser pulse from the same Ti:sapphire laser. Absorption of the laser light exceeding 70% was observed, resulting in an x-ray yield (>1 keV) of
pulse. This may constitute a much simpler means of intense x-ray generation using ultrashort laser pulses as compared to the irradiation of structured / pre-deposited cluster targets, and it offers higher x-ray conversion efficiency than that from gas clusters and planar solid targets.
Betatron Radiation of an Off-axis Injected Electron in a Laser Wakefield Accelerator
Hwang, Seok-Won ; Lee, Hae-June ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 86~91
DOI : 10.3807/JOSK.2009.13.1.086
The electrons injected into a laser wakefield undergo betatron oscillation and give rise to the emission of intense X-ray radiation. To investigate the generation conditions of the X-rays, the relativistic motion of an electron injected in an off-axis position has been simulated with wakefield profiles which are pre-calculated with a two-dimensional particle-in-cell code. The wakefield with a plasma density of
is generated by the laser with an intensity of
and a pulse width of 30 fs. From the calculation of the single particle motion, the characteristics of the betatron radiation are investigated in the time domain. As the transverse injection position increases, the power and the duration time of the radiation increase, but the width of each pulse decreases.
Reduction of Reconstruction Errors in Kinoform CGHs by Modified Simulated Annealing Algorithm
Yang, Han-Jin ; Cho, Jeong-Sik ; Won, Yong-Hyub ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 92~97
DOI : 10.3807/JOSK.2009.13.1.092
In this paper, a conventional simulated annealing (SA) method for optimization of a kinoform computer generated hologram (CGH) is analyzed and the SA method is modified to reduce a reconstruction error rate (ER) of the CGH. The dependences of the quantization level of the hologram pattern and the size of the data on the ER are analyzed. To overcome saturation of the ER, the conventional SA method is modified as it magnifies a Fourier-transformed pattern in the intermediate step. The proposed method can achieve a small ER less than 1%, which is impossible in the conventional SA method.
Optical Wireless Access Point Agent Networks
Lee, Tae-Gyu ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 98~106
DOI : 10.3807/JOSK.2009.13.1.098
This paper proposes an optical wireless transfer agent method which realizes the continuous and swift data transfer of optical wireless terminals in optical wireless networks. The unguided wireless channel generally shows frequent link disconnections and propagation delays due to weak wireless links. Specially speaking, optical wireless channels have more vulnerable links and roaming propagation delays relative to the weakness of the previous RF channels due to their low signal connectivity and small geographic coverage. Conventional optical wireless network protocols did not consider any fault models about physical link faults. Consequently, they have shown data transfer inefficiency for both data link control and physical wireless link control. To overcome these optical wireless environmental problems, this paper suggests a new wireless access point (or base station) agent system, which provides wireless or mobile clients with previous link layer protocols compensated.
Performance Analysis of Chromatic Dispersion Compensation of a Chirped Fiber Grating on a Differential Phase-shift-keyed Transmission
Kim, Sung-Chul ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 107~111
DOI : 10.3807/JOSK.2009.13.1.107
The properties of the chirped fiber Bragg grating (CFBG) as a chromatic dispersion compensator in differential phase-shift-keyed (DPSK) transmission are analyzed. Comparisons of a performance of a CFBG in between DPSK and On-Off Key (OOK) are shown by simulations using the commercial numerical modeling software,
. In the simulation, we compared the performance of the CFBG when they were used in the RZ-OOK 40 Gbps and the RZ-DPSK 40 Gbps transmission. The simulation results show the performance of an overall transmission with a CFBG in DPSK is inferior to the case of OOK, although DPSK generally has a 3 dB higher SNR (signal-to-noise ratio) than OOK.
PMD Effect on the Clock-based Optimum Dispersion Compensation Monitoring Technique
Kim, Sung-Man ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 112~115
DOI : 10.3807/JOSK.2009.13.1.112
We investigate the effect of polarization-mode dispersion (PMD) on the optimum dispersion compensation (ODC) monitoring and nonlinear penalty in optical transmission systems. We report that PMD may reduce the fiber nonlinearity. We also report that the monitoring error of the clock-based ODC monitoring technique decreases after the first-order PMD compensation. A simple explanation of this phenomenon is shown.
A Robust Approach to Automatic Iris Localization
Xu, Chengzhe ; Ali, Tauseef ; Kim, In-Taek ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 116~122
DOI : 10.3807/JOSK.2009.13.1.116
In this paper, a robust method is developed to locate the irises of both eyes. The method doesn't put any restrictions on the background. The method is based on the AdaBoost algorithm for face and eye candidate points detection. Candidate points are tuned such that two candidate points are exactly in the centers of the irises. Mean crossing function and convolution template are proposed to filter out candidate points and select the iris pair. The advantage of using this kind of hybrid method is that AdaBoost is robust to different illumination conditions and backgrounds. The tuning step improves the precision of iris localization while the convolution filter and mean crossing function reliably filter out candidate points and select the iris pair. The proposed structure is evaluated on three public databases, Bern, Yale and BioID. Extensive experimental results verified the robustness and accuracy of the proposed method. Using the Bern database, the performance of the proposed algorithm is also compared with some of the existing methods.
Input-output Coupler System with 45-degree Slant Angle Based on Bragg Hologram
Phan, Anh-Hoang ; Kim, Nam ; Park, Jae-Hyeung ; Lee, Kwon-Yeon ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 123~130
DOI : 10.3807/JOSK.2009.13.1.123
In this paper, we designed and fabricated an input-output coupler system using two or three volume gratings at 632.8nm wavelength. The additional third grating is added at the output coupler to enhance the overall efficiency. The experimental results show that the total system throughput reaches 63% with two-grating and 75% with three-grating input-output coupler. We also present a design method to obtain the desired output power ratio between the gratings.
Layouts and Cells in Integral Photography and Point Light Source Model
Saveljev, Vladimir V. ; Shin, Seung-Jung ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 131~138
DOI : 10.3807/JOSK.2009.13.1.131
The similarity between two groups of displaying methods is demonstrated in two ways, analytically and experimentally. A variety of layouts of the integral photography and display devices based on the point light source model is classified and analyzed in terms of projections and common/separate image planes. In particularly, the transformation matrix is found. Simulation experiments based on the image processing were performed. The layouts, analytical formulas, and experimental results show the similarity of both groups for several layouts.
Resolution-enhanced Reconstruction of 3D Object Using Depth-reversed Elemental Images for Partially Occluded Object Recognitionz
Wei, Tan-Chun ; Shin, Dong-Hak ; Lee, Byung-Gook ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 139~145
DOI : 10.3807/JOSK.2009.13.1.139
Computational integral imaging (CII) is a new method for 3D imaging and visualization. However, it suffers from seriously poor image quality of the reconstructed image as the reconstructed image plane increases. In this paper, to overcome this problem, we propose a CII method based on a smart pixel mapping (SPM) technique for partially occluded 3D object recognition, in which the object to be recognized is located at far distance from the lenslet array. In the SPM-based CII, the use of SPM moves a far 3D object toward the near lenslet array and then improves the image quality of the reconstructed image. To show the usefulness of the proposed method, we carry out some experiments for occluded objects and present the experimental results.
Laser Beam Shaping Using Hollow Optical Fiber and Its Application in Laser Induced Thermal Printing
Yi, Jong-Hoon ; Lee, Kang-In ; Park, Ill-Hyun ; Kwon, Jin-Hyuk ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 146~151
DOI : 10.3807/JOSK.2009.13.1.146
A Gaussian beam of single mode fiber laser was changed into a ring-shaped pattern after it was transmitted through the hollow optical fiber. The ring-shaped beam was focused on a plane by an f-. lens and it was scanned by a Galvano-mirror. The spatial profile of laser energy incident on a plane had two peaks at both sides of the scanned linear track. The profile was compared with the result obtained when the Gaussian beam was dithered transversely by an acousto-optic modulator. It is found that hollow optical fiber beam shaper can replace acousto-optic beam dithering device which is employed in a laser induced thermal printing system.
Enhancement of the Optical Performance by Optimization of Optical Sheets in Direct-illumination LCD Backlight
Park, Gyeung-Ju ; Kim, Young-Gyu ; Yi, Jong-Hoon ; Kwon, Jin-Hyuk ; Park, Jae-Hyun ; Kim, Sung-Hoon ; Kim, Byoung-Ku ; Shin, Jong-Keun ; Soh, Hoi-Sup ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 152~157
DOI : 10.3807/JOSK.2009.13.1.152
The structure of the prism sheet and the reflective polarizer sheet in the direct - illumination liquid crystal display (LCD) backlight is optimized and fabricated. The apex angle of the prism sheet was changed from 90 degree to 96.5 and 101.5 degree and the angular spread of the diffuser films attached on the reflective polarizer sheet was changed from 7 to 1.5 degrees. The measured view angle, the normal luminance, and the contrast ratio from the optimized backlight unit showed improved optical performances.
Characterization of Supercontinuum and Ultraviolet Pulses by Using XFROG
Tsermaa, Baatarchuluun ; Yang, Byung-Kwan ; Kim, Myung-Whun ; Kim, Jin-Seung ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 158~165
DOI : 10.3807/JOSK.2009.13.1.158
We present cross-correlation frequency-resolved optical gating (XFROG) measurements of supercontinuum pulses generated by using a photonic crystal fiber (PCF), and ultraviolet (UV) pulses generated by frequency doubling of infrared ultra-short pulses. Since supercontinuum pulses have broad spectra, XFROG measurement typically requires using an extremely thin nonlinear crystal which has a thickness of sub-ten microns. Instead of using such a thin crystal, we employed a relatively thick crystal which was mounted on a galvanometer in order to achieve a phase-matching over the whole spectral bandwidth of the supercontinuum pulses by a crystal-dithering technique. Experimental results of the retrieved phase and intensity were in fair agreement with the independently measured data.
Hemodynamic Responses of Rat Brain Measured by Near-infrared Spectroscopy During Various Whisker Stimulations
Lee, Seung-Duk ; Koh, Dalk-Won ; Kwon, Ki-Woon ; Lee, Hyun-Joo ; Lang, Yiran ; Shin, Hyung-Cheul ; Kim, Beop-Min ;
Journal of the Optical Society of Korea, volume 13, issue 1, 2009, Pages 166~170
DOI : 10.3807/JOSK.2009.13.1.166
NIRS (Near-infrared spectroscopy) is a relatively, new, non-invasive, and non-ionizing method of measuring hemodynamic responses in thick biological tissues such as the cerebral cortex. In this study, we measured the hemodynamic responses of the rat barrel cortex to whisker stimulation by using a frequency-domain NIRS system. We designed multiple optical probes comprising multi-mode optical fibers and manipulating arms, both of which can be easily applied to small animals. Various electrical stimulations were applied to rat whiskers at different voltage levels and stimulation frequencies. Our results show that the hemodynamic responses are highly dependent on the stimulation voltage level, and not so much on stimulation frequency. This paper suggests that NIRS technology is highly suitable for the study of small animal brains.