• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.11
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• pp.28-34
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• 2015

By incorporating a 966nm near infrared laser, we demonstrated bidirectional current triggering of between 0 and 10mA in a two-terminal planar device based on a highly resistive vanadium dioxide ($VO_2$) thin film grown by a pulsed laser deposition method. A two-terminal planar device, which had an electrode separation of $100{\mu}m$ and a $50{\mu}m-wide$ $VO_2$ conducting layer, was fabricated through ion beam-assisted milling and photolithographic techniques. A bias voltage range for stable bidirectional current triggering was determined by investigating the current-voltage curves of the $VO_2-based$ device in a current-controlled mode. Bidirectional current triggering of up to 10mA was realized by directly illuminating the $VO_2$ film with a focused infrared laser beam, and the transient responses of triggered currents were analyzed when the laser was modulated at various pulse widths and repetition rates. A switching contrast between off- and on-state currents was evaluated as ~3571, and the rising and falling times were measured as ~40 and ~20ms, respectively.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.4
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• pp.11-17
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• 2015

While most switching devices are based on PN junctions, a single layer can realize a switching device in the case of vanadium dioxide($VO_2$) thin films. In this paper, bidirectional current triggering(switching) is demonstrated in a two-terminal planar device based on a $VO_2$ thin film by illuminating the film with an infrared laser at 1550nm. To begin with, a two-terminal planar device, which had a $30{\mu}m$-wide $VO_2$ conducting layer and an electrode separation of $10{\mu}m$, was fabricated. A specific bias voltage range for stable bidirectional laser triggering was experimentally obtained by measuring the current-voltage characteristics of the fabricated device in a current-controlled mode. Then, by constructing a test circuit composed of the device, a standard resistor, and a DC voltage source, connected in series, the transient response of laser-triggered current and its response time were investigated with a DC bias voltage, included in the above specific bias voltage range, applied to the device. In the test circuit with a DC voltage source of 3.35V and a $10{\Omega}$ resistor, bidirectional laser triggering could be realized with a maximum on-state current of 15mA and a switching contrast of ~78.95.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.349-352
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• 2007

In this paper, we describe the modeling of ablation based laser applications for innovative use in the military In the laser ignition system, a metal confinement is ablated with the high intensity pulsed energy, triggering a thermal ignition of the confined high explosives. The constitutive equations for the laser source, deformation of metals, and explosion of energetic materials are described.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.195-198
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• 2002

Demand for high precision measurement of large area is increasing in many industrial fields. White-light Scanning Interferometer(WSI) is a well-known method for 3D profile measurement. However WSI has some limitations in a measurement range because of the sensing mechanism. Therefore, in this paper we use a heterodyne laser interferometer to get over the limitations of a short measurement range in WSI, We suggest a new WSI system combined with heterodyne laser interferometer. This system is aimed at eliminating Abbe error with measuring the focus point directly. With the use of triggering functionality of WSI, we can use this system as a probe of a precision stage such as a probe of CMM. The suggested system gives a repeatability of 87 nm in the absolute distance measurement test under the laboratory environment.

• Journal of Applied Reliability
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• v.5 no.4
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• pp.439-450
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• 2005

Thermal deformation of Digital Television effect friction noise directly. However there was no methods to find and to solve the thermal friction noise which is huge problem in Digital Television In this study, to figure out occurrence cause of friction noise of the product, we measured thermal deformation of the product to organize a triggering device united with Laser Doppler Vibrometer(LDV) which turned occurrence moment of thermal friction noise into a possibility to measure. In conclusion, we could offer an effective information of design, and ensured ESPI(Electronic Speckle Pattern Interferometry) measure technique which is more detailed than the past way.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.60-67
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• 2006

We constructed a TEA $N_2$ laser which consists of spark gap, pulse type high voltage power supply, Blumlein transmission line circuit, laser tube with Ernst electrode. We observed the self-preionization with an optical fiber in the spark gap and laser tube. The higher voltage power supplied to the Blumlein transmission line circuit, the better preionization was. An U-type transformer yielded better stability and output power than an I-type transformer. The discharge time after triggering a spark gap for the U-type transformer was also short. We obtained the stability of $2.7\%$ and output power of $36{\mu}J$ when the optimum conditions of the laser operation were spark gap distance of 6.0 mm, electrode distance in laser tube of 5.0 mm, $N_2$ gas flow rate in spark gap of 1500 cc/min, $N_2$ gas flow rate in laser tube of 4 ${\iota}$/min, output window reflectivity of $40\%$ and repetition rate of 10 Hz.

• Clinical and Experimental Reproductive Medicine
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• v.32 no.4
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• pp.337-346
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• 2005

Objective: The oligosaccharide moieties of glycoproteins and proteoglycans have a vital function in blastocyst differentiation. Concanavalin (ConA), a lectin, is known to bind on the preimplantation embryos, especially on blastocyst. In this study, we investigated whether ConA can modulate the trophoblast development and about the regulating mediator. Also, we investigated whether expansion is enough for hatching procession of the mouse blastocyst. Method: Embryos were collected at 72 h post hCG injection and chemicals were treated after 24 h (96 hr post hCG injection). ConA or calcium ionophore A23187 were exposed to blastocyst and than analysis the developmental process for 48 hr. Intracellular free-$Ca^{2+}$ concentration in trophectoderm was measured with confocal laser microscope after exposing to ConA or calcium ionophore A23187. ConA-pretreated blastocyst exposed to the calcium ionophore A23187 and then analyzed the developmental process. Otherwise ouabain was treated to the blastocyst to block the $Na^+/K^+$-ATPase activity. Results: In contrast to the control blastocyst, the ConA-exposed blastocysts developed beyond the expansion stage with significantly high rate (90.4%) at 12 h post administration. ConA induced an increase the intracellular $Ca^{2+}$ concentration in trophectoderm. Calcium ionophore A23187 also stimulated expansion of blastocyst. Most of the control blastocysts developed to the hatching stage at 144 h post hCG injection. However, strongly 65% of the ConA-exposed embryos were arrested at expanded stage at same time point. The developmental progression rates to hatching stage of both ConA- and calcium ionophore A23187-expose blastocysts were significantly lower than that of the control. However ConA-pretreated embryos developed to the hatching stage like control embryos. Ouabain showed a tendency to delayed the progress to expansion stage but did not inhibit the development to the hatching stage. Conclusion: ConA-mediated expansion is the result of the increase of intracellular free-calcium in blastocyst stage embryo. It is suspected that expansion of the blasocyst is a essential indirect factor in hatching and the calcium may triggering the cellular mechanisms for the both expansion and hatching progression.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.396-399
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• 2002

Intense quasi-monochromatic x-ray irradiation from the linear plasma target is described. The plasma x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 55 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to the molybdenum target by the electric field in the tube, the weakly ionized plasma, which consists of metal ions and electrons, forms by the target evaporating. In the present work, the peak tube voltage was almost equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 55 kV. When the charging voltage was increased, the linear plasma x-ray source grew, and the characteristic x-ray intensities of K-series lines increased. The quite sharp lines such as hard x-ray lasers were clearly observed. The quasi-monochromatic radiography was performed by a new film-less computed radiography system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.289-290
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• 2006

In general, atomic force microscope (AFM) used for metrological purpose has measuring range less than a few hundred micrometers. We design and fabricate an AFM with long measuring range of $200mm{\times}200mm$ in X and Y axes. The whole stage system is composed of surface plate, global stage, microstage. By combining global stage and microstage, the fine and long movement can be provided. We measure the position of the stage and angular motions of the stage by laser interferometer. A piezoresistive type cantilever is used for compact and long term stability and a flexure structure with PZT and capacitive sensor is used for Z axis feedback control. Since the system is composed of various actuators and sensors, a real time control program is required for the implementation of AFM. Therefore, in this work, we designed a multi-axis control program using a FPGA module, which has various functions such as interferometer signal converting, PID control and data acquisition with triggering. The control program achieves a loop rate more than 500 kHz and will be applied for the measurement of grating pitch and step height.

• Biomaterials Research
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• v.22 no.4
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• pp.303-310
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• 2018

Background: Photodynamic therapy (PDT) is photo-treatment of malignant or benign diseases using photosensitizing agents, light, and oxygen which generates cytotoxic reactive oxygens and induces tumour regressions. Several photodynamic treatments have been extensively studied and the photosensitizers (PS) are key to their biological efficacy, while laser and oxygen allow to appropriate and flexible delivery for treatment of diseases. Introduction: In presence of oxygen and the specific light triggering, PS is activated from its ground state into an excited singlet state, generates reactive oxygen species (ROS) and induces apoptosis of cancer tissues. Those PS can be divided by its specific efficiency of ROS generation, absorption wavelength and chemical structure. Main body: Up to dates, several PS were approved for clinical applications or under clinical trials. $Photofrin^{(R)}$ is the first clinically approved photosensitizer for the treatment of cancer. The second generation of PS, Porfimer sodium ($Photofrin^{(R)}$), Temoporfin ($Foscan^{(R)}$), Motexafin lutetium, Palladium bacteriopheophorbide, $Purlytin^{(R)}$, Verteporfin ($Visudyne{(R)}$), Talaporfin ($Laserphyrin^{(R)}$) are clinically approved or under-clinical trials. Now, third generation of PS, which can dramatically improve cancer-targeting efficiency by chemical modification, nano-delivery system or antibody conjugation, are extensively studied for clinical development. Conclusion: Here, we discuss up-to-date information on FDA-approved photodynamic agents, the clinical benefits of these agents. However, PDT is still dearth for the treatment of diseases in specifically deep tissue cancer. Next generation PS will be addressed in the future for PDT. We also provide clinical unmet need for the design of new photosensitizers.