• Current Optics and Photonics
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• 제2권3호
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• pp.250-260
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• 2018

A pressure wave created by the photoacoustic effect is affected by the medium and by laser parameters. The effect of these parameters on the generated pressure wave can be seen by solving the photoacoustic wave equation. These solutions which are examined in the time domain and the frequency domain should be considered by researchers in acoustic sensor design. In particular, frequency domain analysis contains significant information for designing the sensor. The most important part of this information is the determination of the operating frequency of the sensor. In this work, the laser parameters to excite the medium, and the acoustic signal parameters created by the medium are analyzed. For the first time, we have obtained solutions for situations which have no frequency domain solutions in the literature. The main focal point in this work is that the frequency domain solutions of the acoustic wave equation are performed and the effects of the frequency analysis of the related parameters are shown comparatively from the viewpoint of using them in acoustic sensor designs.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.790-793
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• 2000

We have fabricated good quality superconducting YBa$_2$Cu$_3$$O_{7-x}$(YBCO) thin films on Hastelloy(Ni-Cr-Mo alloys) metallic substrates with CeO$_2$and BaTiO$_3$buffer layers in-situ by pulsed laser deposition in a multi-target processing chamber. YBCO film with CeO$_2$ single buffer layer shows T$_{c}$ of 71.64 K and the grain size less than 0.1 ${\mu}{\textrm}{m}$. When BaTiO$_3$is used as a single buffer layer, the grain size of YBCO is observed to be larger than that of YBCO/CeO$_2$by 200 times and the transition temperature of the film is enhanced to be about 84 K. CeO$_2$/BaTiO$_3$double buffer layer has been adopted to enhance the superconducting properties, which results in the enhancement of the critical temperature and the critical current density to be about 85 K and 8.4 $\times$ 10$^4$ A/cm$^2$ at 77 K, respectively mainly due to the enlargement of the grain size of YBCO film.ilm.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.138-139
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• 2017

This paper describes the design and implementation of a trigger circuit which can be series connected with main pulse circuit for a xenon flash lamp driver. For generating high voltage, the trigger circuit is designed as an inductive energy storage pulsed power modulator with 2 state step-up circuit consisting of a boost converter and a flyback circuit. In order to guarantee pulse width, a resonant capacitor on the output side of the flyback circuit is designed. This capacitor limits the output voltage to protect the flyback switch. In addition, to protect another power supply of xenon flash lamp driver from trigger pulse, the high voltage transformer which can carry the full current of main pulse is designed. To verify the proposed design, the trigger circuit is developed with the specification of maximum 23 kV, 0.6 J/pulse output and tested with a xenon flash lamp driver consisting of a main pulse circuit and a simmer circuit.

• 한국전기전자재료학회논문지
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• 제13권11호
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• pp.959-962
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• 2000

We have fabricated good quality superconducting YBa$_2$Cu$_3$$O_{7-x}$(YBCO) thin films on Hastelloy(Ni-Cr-Mo alloys) metallic substrates with CeO$_2$and BaTiO$_3$buffer layers in-situ by pulsed laser deposition in a multi-target processing chamber. YBCO film with CeO$_2$single buffer layer shows T$_{c}$ of 71.64 K and the grain size less than 0.1${\mu}{\textrm}{m}$. When BaTiO$_3$ is used as a single buffer layer, the grain size of YBCO is observed to be larger than that of YBCO/CeO$_2$by 200 times and the transition temperature of the film is enhanced to be about 84 K. CeO$_2$/BaTiO$_3$double buffer layer has been adopted to enhance the superconducting properties, which results in the enhancement of the critical temperature and the critical current density to be about 85 K and 8.4$\times$10$^4$ A/$\textrm{cm}^2$ at 77 K, respectively mainly due to the enlargement of the grain size of YBCO film.ilm.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2005년도 Proceedings of The 6th korea-china joint workshop on nuclear waste management
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• pp.76-85
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• 2005

The conceptual study of Accelerator Driven System (ADS) had lasted for about five years and ended in 1999 in China. As one project of 'the major state basic research program (973)' in energy domain, which is sponsored by the China Ministry of Science and Technology (MOST), a five years program of basic research for ADS physics and related technology has been launched since 2000 and passed national review last month. CIAE (China Institute of Atomic Energy), IHEP (Institute of High Energy Physics), PKU-IHIP (Institute of Heavy Ion Physics in Peking University) and other institutions are jointly carrying on the research. The research activities are focused on HPPA physics and technology, reactor physics of external source driven sub-critical assembly, nuclear data base and material study. For HPPA, a high current injector consisting of an ECR ion source, LEBT and a RFQ accelerating structure of 3.5MeV has been built. In reactor physics study, a series of neutron multiplication experimental study has been carried out and is being carrying on. The VENUS facility has been constructed as the basic experimental platform for the neutronics study in ADS blanket. It's a zero power sub-critical neutron multiplying assembly driven by external neutron produced by a pulsed neutron generator. The theoretical, experimental and simulation study on nuclear data, material properties and nuclear fuel circulation related to ADS is carrying on to provide the database for ADS system analysis. The main results on ADS related researches will be reported.

• 한국표면공학회지
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• 제45권2호
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• pp.53-60
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• 2012

Modulated Pulse Power (MPP) magnetron sputtering is a new high-power pulsed magnetron sputtering (HPPMS) technology which overcomes the low deposition rate problem by modulating the pulse voltage shape, amplitude, and the duration. Highly ionized magnetron sputtering can be performed without arcing because it can be controlled as multiple steps of micro pulses within one overall pulse period in the range of 500-3,000 ${\mu}s$. In this study, the various waveforms of discharge voltage and current for micro pulse sets of MPP were investigated to find the possibility of controlling the strongly ionized plasma mode. Enhanced ionization of the sputtered metal atoms was obtained by OES. Large grained columnar structure can be grown by the strongly ionized plasma mode in the AZO deposition using MPP. In the most highly ionized deposition condition, the preferred orientation of (002) plane decreased, and the resistivity, therefore, increased by the plasma damage.

• Current Optics and Photonics
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• 제3권5호
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• pp.466-472
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• 2019

A system for continuous-wave coherent Doppler lidar (CW lidar), made up of all-fiber structures and a coaxial transmission telescope, was set up for wind measurement in Hefei (31.84 N, 117.27 E), Anhui province of China. The lidar uses a fiber laser as a light source at a wavelength of $1.55{\mu}m$, and focuses the laser beam on a location 80 m away from the telescope. Using the CW lidar, radial wind measurement was carried out. Subsequently, the spectra of the atmospheric backscattered signal were analyzed. We tested the noise and obtained the lower limit of wind velocity as 0.721 m/s, through the Rayleigh criterion. According to the number of Doppler peaks in the radial wind spectrum, a classification retrieval algorithm (CRA) combining a Gaussian fitting algorithm and a spectral centroid algorithm is designed to estimate wind velocity. Compared to calibrated pulsed coherent wind lidar, the correlation coefficient for the wind velocity is 0.979, with a standard deviation of 0.103 m/s. The results show that CW lidar offers satisfactory performance and the potential for application in wind measurement.

• 대한금속재료학회지
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• 제56권12호
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• pp.854-860
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• 2018

In spite of the many attractive properties of (W,Ti)C, its low fracture toughness limits its wide application. To improve the fracture toughness generally a second phase is added to fabricate a nanostructured composite. In this regard, graphene was considered as the reinforcing agent of (W,Ti)C. (W,Ti)C-graphene composites that were sintered within 2 min using pulsed current activated heating under a pressure of 80 MPa. The rapid consolidation method allowed retention of the nano-scale microstructure by blocking the grain growth. The effect of graphene on the hardness and microstructure of the (W,Ti)C-graphene composite was studied using a Vickers hardness tester and FE-SEM. The grain size of (W,Ti)C was reduced remarkably by the addition of graphene. Furthermore, the hardness decreased and the fracture toughness improved with the addition of graphene.

• Current Optics and Photonics
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• 제6권4호
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• pp.407-412
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• 2022

We report on a diode-laser-pumped mode-locked Yb:KGW laser system, which delivers ultrashort pulses down to 89 fs at a repetition rate of 63 MHz, with an average power of up to 5.6 W. A fiber-coupled diode laser at 981 nm, operated with a compact driver, is used to optically pump the gain crystal via an off-axis parabolic mirror. A semiconductor saturable-absorber mirror is used to initiate the pulsed operation. Laser characteristics such as the pulse duration, spectrum bandwidth, and output power are investigated by varying the intracavity dispersions via changing the number of bounces between negative-dispersive mirrors within the cavity. Short pulses with a duration of 89 fs, a center wavelength of 1,027 nm, and 3.6 W of output power are produced at a group-velocity dispersion (GVD) of -3,300 fs². As the negative GVD increases, the pulse duration lengthens but the output power at the single-pulse condition can be enhanced, reaching 5.6 W at a GVD of -6,600 fs². Because of pulse broadening at high negative GVDs, the highest peak intensity is achievable at a moderate GVD with our system.

• E2M - 전기 전자와 첨단 소재
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• 제16권9호
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• pp.63.2-64
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• 2003

Epitaxial yttrium-stabilized HfO$_2$ thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si.(100)HfO$_2$ and [001]Si/[001]HfO$_2$. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion, X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf-Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO$_2$ thin film on bare Si is via a direct growth mechanism without involoving the reaction between Hf atoms and SiO$_2$ layer. High-frequency capacitance-voltage measurement on an as-grown 40-A yttrium-stabilized HfO$_2$ epitaxial film yielded an dielectric constant of about 14 and equivalent oxide thickness to SiO$_2$ of 12 A. The leakage current density is 7.0${\times}$ 10e-2 A/$\textrm{cm}^2$ at 1V gate bias voltage.