• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4063-4068
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• 2012

Oxide substrates in semiconductor-sensitized solar cells (SSSCs) have a great impact on their performance. $TiO_2$ has long been utilized as an oxide substrate, and other alternatives such as ZnO and $SnO_2$ have also been explored due to their superior physical properties over $TiO_2$. In the development of high-performance SSSCs, it is of significant importance to understand the effect of oxides on the electron injection and charge recombination as these two are major factors in dictating solar cell performance. In addition, elucidating the relationship between these two critical processes and solar cell performance in each oxide is critical in building up the basic foundation of SSSCs. In this study, ultrafast pump-probe laser spectroscopy and open-circuit decay analysis were conducted to examine the characteristics of three representative oxides ($TiO_2$, ZnO, and $SnO_2$) in terms of electron injection kinetics and charge recombination, and the implication of results is discussed.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.535-541
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• 2005

We report on the development of a passively mode-locked near-infrared femtosecond laser with Cr:YAG crystal that operates near room temperature. The laser wavelength could easily be tuned by using only the internal prism pair over 110 nm from 1400 nm to 1510 nm in cw and over about 30 nm in mode-locked operation, respectively Maximum cw output powers of 810 mW were obtained with $1.5 \%$ output coupler for absorbed pump powers of 7.6 W. For compensation of the internal group velocity dispersion, an IR graded prism pair was used. The Cr:YAG laser delivered nearly Fourier-transform limited pulses with a pulse duration as short as 64 fs at 100 MHz repetition rate. In the mode-locked regime, the laser was operating at 1510 nm with a spectral bandwidth of 44 nm. In order to avoid unstable mode-locking and power instabilities, self-built tubes were inserted into the beam path in the resonator and purged with N2 gas. Finally, output powers of the Cr:YAG laser were optimized to 250 mW fer long time stable mode-locked operation.

• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.18-24
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• 2010

A Ka-band microstrip array antenna for wide-range detection of moving targets is analyzed through a photonicassisted reactive-near-field characterization technique. The antenna array employs a 3-dB-tapered feed network to suppress the sidelobe level while retaining a wide azimuth beamwidth for a wide detection range. The relative nearelectric field patterns of the array and its 3-dB-tapered feed lines have been measured using an electro-optic fieldmapping technique for minimally invasive millimeter-wave sensing. A number of typical limitations on the technique, involving bandwidth, low signal-modulation depth, and high laser-induced noise in high-frequency applications, have been overcome by suppressing the carrier portion of the optical interrogation beam.

• Korean Journal of Optics and Photonics
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• v.12 no.6
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• pp.503-506
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• 2001

When DC voltages from 5 V up to 90 V are applied to a transmitter chip excited by an ultrafast lacer beam, the terahertz electromagnetic pulses and their spectra are changed. The spectrum shifts to the high frequency range when the high DC voltage is applied to the chip. At that time, the signal-to-noise ratio is increased from 250: 1 to 10,000: 1. The spectrum can expand up to 4 THz by optimal realignment of the THz system. Also, two terahertz electromagnetic pulses are generated from a receiver chip when the laser detection beam is reflected to the back side of the chip.

• Proceedings of the Korean Magnestics Society Conference
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• 2010.06a
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• pp.94-94
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• 2010

Co/Pd multilayer systems have been investigated with much attention for a long time due to the high and easily controllable perpendicular magnetic anisotropy. Two [Pd(1)/Co(0.4 nm)]5 multilayer systems - one is as-deposit, and the other is annealed at $350^{\circ}C$ - are studied with an all-optical approach. A two-color optical pump probe setup using 30 fs laser pulse at 82 MHz repetition rate is used to measure the time-resolved magneto-optical Kerr signal. It turns out the heat treatment enhances the perpendicular magnetic anisotropy, and leads to faster magnetization precession. The frequency reaches 30 GHz in the annealed sample, which is a factor of 2 larger compared to the as-deposit film.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.54-59
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• 2008

We report on the measurements of absorption spectra from acetylene ($^{12}C_2H_2$) and hydrogen cyanide ($H^{13}C^{14}N$) for wavelength reference in the C-band (conventional band) region using a supercontinuum optical source generated from a mode-locked $Cr^{4+}$:YAG laser. The center wavelength of the mode-locked $Cr^{4+}$:YAG laser was 1510 nm and the pulse duration was 75 fs at 100 MHz repetition rate. The supercontinuum source achieved a flatness of ${\pm}5dB$ over a wavelength range of more than 400 nm, using a 20 m long photonic crystal fiber. The measured absorption spectra from acetylene ($^{12}C_2H_2$) and hydrogen cyanide ($H^{13}C^{14}N$) had more than 50 lines and were analyzed for wavelength standardization.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.927-933
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• 2011

This paper presents an optical sampling technique which can be used to overcome the limited bandwidth of a commercial electronic sampling oscilloscope for pulsed signal measurement. Employing an ultrafast laser with 0.1 ps pulse duration, 20 GHz electromagnetic pulses were generated through a fast photodiode. These pulses were transmitted through a microstrip line and sampled with an optically triggered electro-optic system. Two sampled 20 GHz pulses - measured independently over the transmission line with a non-contacting electro-optic method and conventional electronic one through a coaxial cable - were compared.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.300-307
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• 2022

Time-resolved serial femtosecond crystallography (TR-SFX) is a powerful technique for determining temporal variations in the structural properties of biomacromolecules on ultra-short time scales without causing structure damage by employing femtosecond X-ray laser pulses generated by an X-ray free electron laser (XFEL). The mixing rate of reactants and biomolecule samples, as well as the hit rate between crystal samples and x-ray pulses, are critical factors determining TR-SFX performance, such as accurate image acquisition and efficient sample consumption. We here develop two distinct sample delivery systems that enable ultra-fast mixing and on-demand droplet injecting via pneumatic application with a square pulse signal. The first strategy relies on inertial mixing, which is caused by the high-speed collision and subsequent coalescence of droplets ejected through a double nozzle, while the second relies on on-demand pneumatic jetting embedded with a 3D-printed micromixer. First, the colliding behaviors of the droplets ejected through the double nozzle, as well as the inertial mixing within the coalesced droplets, are investigated experimentally and numerically. The mixing performance of the pneumatic jetting system with an integrated micromixer is then evaluated by using similar approaches. The sample delivery system devised in this work is very valuable for three-dimensional biomolecular structure analysis, which is critical for elucidating the mechanisms by which certain proteins cause disease, as well as searching for antibody drugs and new drug candidates.