Woohong Kim

High refractive index optical polymer material has attracted interests in the advanced photoelectronic applications, such as microlens array, optical encapsulates for OLEDs and directional light-scattering filter. One of the approaches to reinforce the refractive index of a polymer is adding nanoparticles with a high index. Effective media approximation (EMA) theories have widely

We report the latest progress on fabrication of rare earth doped single crystal yttrium aluminum garnet (YAG) core/undoped YAG cladded fibers. Rare-earth doped single crystal core fibers were grown with laser heated pedestal growth methods. In a second step, epitaxial methods were used to grow a single crystalline undoped YAG cladding onto the core fiber. Hydrothermal and liquid phase epitaxy methods utilize the core doped fiber as the seed. X-ray diffraction of cladding reveals an equilibrium (110) morphology. Energy-dispersive X-ray spectroscopy analysis shows there is minimal diffusion of rare-earth dopants into the cladding structure. The use of scandium doping is shown to substitute at the Al³⁺ site, thereby allowing an additional tunability of refractive index of core structure material besides conventional Y³⁺ site dopants. The use of these epitaxial growth methods enables material compatibility, tuning of refractive index, and conformal growth of cladding structures onto core fibers for optical devices.

This note amends the author list of a recent publication [Appl. Opt. 54, F210 (2015) [CrossRef] ].

High purity Yb3+ doped Lu2O3 powder has been synthesized by the co-precipitation method. The powders underwent a jet milling at various feed rate using a commercial jet mill machine. It is found that jet milling is very effective in breaking up of large agglomerates without cross-contamination. Median agglomerate size decreased from 8.74 μm to 1.06 μm when jet milled at a feed rate 0.75 lb/hr. There was no noticeable increase in impurities picked up during the jet milling process in the final powder obtained after a sacrificial run that was carried out for the purpose of conditioning the surface of the liner. Homogeneous, uniform, and highly transparent ceramic was obtained from the ceramic hot pressed with the final jet milled powder compared to the one made from as-produced powder where some defects and splotches are often observed. Transmission of the Yb3+:Lu2O3 ceramics obtained from the jet milled powder is very close to the theoretical limit, demonstrating the excellent quality of the transparent ceramic.

We present a method of Cu(In,Ga)S₂ (CIGS) thin film formation via conversion of layer-by-layer (LbL) assembled Cu-In-Ga oxide (CIGO) nanoparticles and polyelectrolytes. CIGO nanoparticles were created via a novel flame-spray pyrolysis method using metal nitrate precursors, subsequently coated with polyallylamine (PAH), and dispersed in aqueous solution. Multilayer films were assembled by alternately dipping quartz, Si, and/or Mo substrates into a solution of either polydopamine (PDA) or polystyrenesulfonate (PSS) and then in the CIGO-PAH dispersion to fabricate films as thick as 1–2 microns. PSS/CIGO-PAH films were found to be inadequate due to weak adhesion to the Si and Mo substrates, excessive particle diffusion during sulfurization, and mechanical softness ill-suited to further processing. PDA/CIGO-PAH films, in contrast, were more mechanically robust and more tolerant of high temperature processing. After LbL deposition, films were oxidized to remove polymer and sulfurized at high temperature under flowing hydrogen sulfide to convert CIGO to CIGS. Complete film conversion from the oxide to the sulfide is confirmed by X-ray diffraction characterization.

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Ceramic laser materials have come a long way since the first demonstration of lasing in 1964. Improvements in powder synthesis and ceramic sintering as well as novel ideas have led to notable achievements. These include the first Nd:yttrium aluminum garnet (YAG) ceramic laser in 1995, breaking the 1 KW mark in 2002 and then the remarkable demonstration of more than 100 KW output power from a YAG ceramic laser system in 2009. Additional developments have included highly doped microchip lasers, ultrashort pulse lasers, novel materials such as sesquioxides, fluoride ceramic lasers, selenide ceramic lasers in the 2 to 3 μm region, composite ceramic lasers for better thermal management, and single crystal lasers derived from polycrystalline ceramics. This paper highlights some of these notable achievements.

We have synthesized high‐purity Yb³⁺‐doped Lu₂O₃ powder by the coprecipitation method. We have demonstrated that the recrystallization of the metal nitrates greatly improve the chemical purity of the resulting oxides. From thermogravimetry and differential thermal analysis study, we have calculated the approximate formula of the oxinitrate precipitate precursor as Lu_1.8Yb_0.2(OH)_5.44(NO₃)_0.56·0.58H₂O. Fine and soft agglomerate powders were obtained after calcinations. We have shown that the powder is mainly in the form of polycrystalline soft agglomerates composed with 15–20 nm size crystals. The resulting ceramic showed higher transparency (close to theoretical limit) compared with the ones fabricated with commercial powders.