Cha‐Hwan Oh

We successfully synthesized the addition-type polynorbonenes (PNB) exhibiting photochromic properties and excellent thermal stability. Three norbornene-based monomers with different azobenzene moiety (R=NO2, H, OCH3) were synthesized by transesterification method. The corresponding PNB copolymers were synthesized by transition metal-catalyzed addition polymerization method, and characterized by GPC, UV-Vis spectroscopy, NMR, and thermal analysis. For comparison of the photochromic properties dep

We studied the nonlinear optical properties of ZnO nanorods. ZnO nanorods were deposited by using the electro-deposition method, and these samples were annealed at a temperature of 400 ˚C for 5 hours. The nonlinear absorption properties of ZnO nanorods with two different rod diameters of 500 nm and 100 nm were measured by using the femtosecond nonlinear transmission method at an incident wavelength of 800 nm. The nonlinear absorption coefficients of ZnO nanorods were 5.9 × 10−7 cm/W and 2.3 × 10

The temperature dependence of electromagnetically induced transparency (EIT) in a Cs atomic vapor cell was investigated. A probe laser beam frequency was scanned around the resonance frequency of the transition line 6S$_{1/2}$, F = 3 $\rightarrow$ 6P$_{3/2}$, F$'$ = 4 while the coupling beam frequency was locked to the transition line 6S$_{1/2}$, F = 4 $\rightarrow$ 6P$_{3/2}$, F$'$ = 4. In order to analyze the temperature dependence of the EIT signal quantitatively, we calculated the dispersion

It was found that a surface relief grating-patterned glass (SRG-PG) could align the nematic liquid crystal (LC) along the groove direction. The LC alignment on the SRG-PG substrate was investigated by measuring the transmittance of a 90-twisted nematic liquid crystal (TNLC)-cell located between crossed polarizers. The SRG-PG was prepared by recording a holographic grating on the photoresist (PR)-coated glass and then etching the PR. The atomic-force-microscopy results show that the groove spacin

We observed theuorescence induced by the energy-pooling collision process in a heated Csatomic vapor cell. Theuorescence from the heated Cs atomic vapor cell showed about 30 spectralpeaks, and all the peaks could be assigned to the Cs atomic transition lines. The radiation trappingeffect and the optical thickness of the heated Cs atomic vapor were considered to correctly analyzethe energy-pooling collision process. The ratios of the atomic populations in each level involved inthe energy-pooling

Absorption of cw-CO₂ laser lines by CH₃I molecule is investigated. Relative absorption coefficients are obtained by measuring optoacostic signals fran the CH I cell of 6 torr filling pressure. Quantum number assignments to the absorption lines are carried out through the numerical calculations, and the rotational quantum numbers of the upper and the lower levels and the vibrational modes of 12 absorption lines are identified.

Because of an increase in applications for photonic crystals, many efforts have been made to fabricate large-area, uniform photonic crystal structures, but the fabrication of such photonic crystal structures is not easy because of some limitations in optimizing both the uniformity and the large area. In this paper, we examined the wedge-shaped cell method, which has advantage for forming uniform photonic crystal structure because it generates a meniscus in line. Optimum conditions for the fabric

The surface structuring of amorphous and crystalline silicon was performed by using femtosecondlaser-induced phase transformations: i) amorphous-to-crystalline and ii) crystalline-to-amorphous. The amorphous silicon (a-Si) films were prepared on glass substrates by using plasma-enhanced chemical-vapor deposition. Two kinds of micropatterns were produced in the a-Si films: i) a twodimensional (2D) pattern (a word ‘q-Psi’) was produced by using the inverse Fourier transform of a computer-generated h

A photonic crystal structure was fabricated by using a flow-controlled vertical deposition (FCVD) method. We simplified the fabrication setup by replacing the peristaltic pump with just an open hole at the bottom of beaker. The optimum surface drop velocity of the polystyrene suspension for a photonic crystal structure with uniform surface and thickness was experimentally determined to be 0.35 μm/s. The photonic band-gap behavior of the fabricated photonic crystal structure was analyzed by using

A surface relief grating (SRG) can be formed by illuminating an azo polymer film with two interfering beams. The SRG is applicable to diffractive optical elements, to anchoring of a liquid crystal, and recently to photonic crystal fabrication. In this research, we investigated the effect of gold nano particles on the formation of SRGs on two kinds of azo polymer films. The SRGs were formed by using the two-beam interference technique, and the shapes and the heights of the SRGs at various content

Boronization with carborane (C2B10H12) was archieved in a vacuum vessel coupled to a filamentdischarge system. Optical emission spectroscopy was employed to characterize the boronizationprocess. The Balmer lines of hydrogen and deuterium were measured, and the boronization processwas analyzed by using the intensity ratio of the H to the D line (IH/ID). The relation betweenthe pressure and the intensity ratio was investigated, and the thickness of the deposited boron filmwas predicted. Also, the

Photoinduced anisotropy and birefringence in an azobenzene polymer film were investigated by pumping beams with various wavelengths. Azobenzene-type polymer whose and n transition bands are far enough from each other to be distinguished was used in this experiment. The vertical and the parallel polarization components of the absorbance and also the birefringence on the polymer film were measured simultaneously during pumping with a linearly polarized beam at various wavelengths. We observed ab