Bum Ku Rhee
Sogang University
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Publication
Featured researches published by Bum Ku Rhee.
Applied Physics Letters | 2001
Yunjin Choi; June-H. Park; Myong R. Kim; Wonho Jhe; Bum Ku Rhee
We present direct observation of self-focusing near the diffraction limit by measuring the beam-spot size with a scanning fiber probe tip. We have used the polycrystalline silicon film, which exhibits a reverse-saturation (Im χ(3)≈8×10−3 esu) and self-focusing (Re χ(3)≈2×10−2 esu), as measured by the conventional z-scan method with He–Ne laser. It is observed that the beam radius of about its wavelength becomes smaller as the input laser intensity is increased, which indicates that the self-focusing effect dominates over the reverse saturation in the 300-nm-thick sample.
Applied Physics Letters | 1998
Sang-Hoon Yim; Dong-Ryeol Lee; Bum Ku Rhee; Doseok Kim
A saturable absorber Cr4+:YAG, used for a passive Q switching of Nd:YAG laser was studied in order to understand the physical mechanism of nonlinear absorption (photobleaching). An optical bleaching experiment was carried out using the two pulsed lasers with duration of pico- and nanoseconds at 1.064 μm wavelength. Experimental results were compared with numerical analysis of theoretical rate equations with all relevant energy levels. The inclusion of intersystem crossing between singlet- and triplet-excited states with reasonable rate of transition kisc was necessary to explain the difference in the saturation behaviors for nanosecond and picosecond laser pulses.
Applied Optics | 2002
Changsoo Jung; Bum Ku Rhee
We present a novel method for determining both the thickness and the optical constants of a weakly absorbing thin film upon a nearly transparent substrate through analysis of transmittance measured at various incident angles with coherent light. We demonstrate this method for a polymer thin film. The refractive indices and extinction coefficients of poly(DRI-anthranilic acid) at wavelengths of 1,064, 632.8, and 532 nm were determined for the first time to our knowledge. We also confirmed the validity of our method with a polystyrene thin film whose optical constant was known. It was found that a thickness of a few hundred nanometers can easily be measured and that this method offers simplicity as well as the capability of in situ measurement.
Rapid Communications in Mass Spectrometry | 2009
Soo-Jin Park; Wha-Keun Ahn; Sunyoung Lee; Sang Yun Han; Bum Ku Rhee; Han Bin Oh
Ultraviolet (UV) photodissociation (PD) experiments using 266 nm light were performed for a series of phosphopeptide cations in a Fourier transform mass spectrometer. The objective of the experiments was to determine whether 266 nm UV irradiation on the phosphopeptide cations would induce unique peptide backbone dissociation. In addition, the general behavior of the phosphate loss (-80 or -98 Da) was monitored, particularly for those phosphopeptides with a phosphotyrosine residue that itself is a UV chromophore. For phosphopeptides with a UV chromophore, their photodissociation behavior was very similar to that of low-energy sustained off-resonance irradiation collisionally activated dissociation (SORI-CAD), with a few exceptions. For example, b- and y-type peptide backbone fragments were prevalent, and their dephosphorylation behavior was consistent with that of the SORI-CAD results. For phosphoserine peptides, the loss of a phosphate group was always observed. On the other hand, for phosphotyrosine peptides, the phosphate loss was found to be dependent on the presence of a basic amino group in the sequence and the charge state of the precursor ions, in agreement with the CAD results in the literature. However, hydrogen atom loss or aromatic side chain loss, which is known to be the excited state specific fragmentation pathway, was rarely observed in our 266 nm UV PD experiments, in contrast to the previous UV PD literature (particularly at 220 nm). The mechanism for these observations is described in terms of dominant internal conversion followed by intramolecular vibrational energy redistribution (IVR).
Macromolecular Research | 2007
Ju Yeon Lee; Jin Hyang Kim; Bum Ku Rhee
Abstract3,4-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-4′-nitrostilbene dianhydride was prepared and reacted with 4,4′-(hexafluoroisopropylidene)dianiline to yield a novel Y-type polyimide containing the 3,4-dioxynitrostilbenyl group as an NLO-chromophore, which constituted part of the polymer backbone. The resulting polyimide was soluble in polar solvents such as acetone andN,N-dimethylformamide. The polymer exhibited good thermal stability up to 370 °C in the thermogravimetric analysis. The glass-transition temperature (Tg) obtained from the differential scanning calorimetry thermogram was near to 153 °C. The second harmonic generation (SHG) coefficient (d33) of the poled polymer film at the fundamental wavelength of 1064 cm−1 was around 2.15 × 10−8 esu (9.01 pm/V). The dipole alignment exhibited exceptionally high thermal stability even at a temperature 30 °C above theTg, and there was no SHG decay below 180 °C because of the partial main chain character of the polymer structure.
Journal of The Optical Society of Korea | 1997
Chang-Wook Han; Doo Jin Cho; Bum Ku Rhee
Rigorous coupled-wave analysis (RCWA) with a simplified eigenvalue problem is used to investigate the an-tireflective property of one-dimensional surface-relief gratings such as binary gratings, triangular gratings and gratings with triangle-like surface profiles. The convergence of RCWA is investigated by varying the number of layers and the number of space-harmonics used in the computation. For unpolarized light normally incident on a medium of refractive index 1.64 from vaccum, a triangle-like grating shows the reflectivity of
Optics Communications | 2001
Bong Gi Kim; Bum Ku Rhee
1.6 {\times} 10^{-4}
Optics Express | 2007
Hwan-Hong Lim; Om Prakash; Byeong-Joo Kim; Krishnamoorthy Pandiyan; Myoungsik Cha; Bum Ku Rhee
in contrast to a minimum reflectivity of
Macromolecular Research | 2004
Kuk Ro Yoon; Hoosung Lee; Bum Ku Rhee; Chang Soo Jung
3.8 {\times} 10^{-3}
Optics Letters | 2006
Jisoo Hwang; Min Jung Kim; J. W. Wu; Seung Mook Lee; Bum Ku Rhee
for a binary grating. We also study the dependence of reflectivity on the wavelength, and on the angle of incidence for a groove shape and depth which result in minimum reflectivity.