Sung-Hyo Yun

Mechanisms of upconverted fluorescence in an Er3+ doped LiNbO3 single crystal

Two different upconversion mechanisms leading to green fluorescence in an Er3+ doped LiNbO3 crystal have been investigated with pulse laser excitations at the wavelengths of 1064 and 980 nm. In the case of the 1064 nm pump, the Er3+ ions become excited by the phase‐matched second harmonic wave generated in the LiNbO3 crystal, whereas sequential two‐photon absorption is mainly responsible for the excitation with the 980 nm pump. The second harmonic excitation is of an order of magnitude more efficient than the sequential two photon excitation in the upconversion of the near‐infrared pump photons to the green fluorescence.

Characteristics of critically phase-matched second-harmonic generation of a Li2B4O7 crystal grown by the Czochralski method

Abstract The characteristics of a lithium diborate (Li 2 B 4 O 7 ) crystal grown by the Czochralski method for critically phase-matched second-harmonic generation (SHG) at a fundamental wavelength of 1064 nm from a pulsed Nd: YAG laser are discussed. The phase matching angle, angular acceptance bandwidth, and the temperature bandwidth of type I SHG are reported.

Spectroscopic properties of Ce3+ ions in a barium-sodium borate glass

Abstract We studied the spectroscopic properties of Ce 3+ ions in a borate glass through optical absorption, excitation, time-resolved fluorescence, and excited state absorption (ESA) measurements. The Stark levels of the 5d-state, fluorescence properties of the 5d → 4f transition, and the nonradiative transition process from the lowest Stark level of the 5d-state are reported. The ESA from the lowest Stark level of the 5d-state to a higher energy state was also investigated.

Second harmonic generation in the Gd2(MoO4)3 crystal grown by the Czochralski method

Abstract The characteristics of the second harmonic generation (SHG) in the Gd 2 (MoO 4 ) 3 crystal grown by the Czochralski method were investigated at 1.064 μm light from an Nd: YAG laser. The phase matching angle, angular acceptance bandwidth and the temperature bandwidth were measured in type I phase matching. The nonlinear coefficient and SHG conversion efficiency were also obtained.

Volcanological Interpretation of Historical Eruptions of Mt. Baekdusan Volcano

This study is performed to find out the eruptive events of the historical period recorded in literature, which have been recognized and regarded as ones from Mt. Baekdusan, and to make volcanological interpretations of the eruptive events. Since the Millennium eruption, more than 31 eruptive events have been discovered, most of which are Plinian eruptions with volcanic ash that dispersed into the regions in the vicinity of the volcano. The 1903 record includes the event of the phreatomagmatic or vulcanian eruption that occurred within the Cheonji caldera lake. Based on the eruption records of the historical period and the 2002 precursor unrest to volcanic eruptions, Mt. Baekdusan has been evaluated and regarded as an active volcano that has the potential to erupt in the future.

Linear optical properties and characteristics of critically phase-matched second harmonic generation of a Li2B4O7 crystal grown by the Czochralski method

The refractive indices of a lithium diborate (Li2B4O7) crystal grown by the Czochralski method have been measured and the characteristics of this crystal for critically phase-matched second harmonic generation (SHG) at fundamental wavelengths of NIR region are discussed. The phase matching angles and angular acceptance bandwidths of type I SHG are reported.

Petrology of the Basalts in the Seongsan-Ilchulbong area, Jeju Island

This study reports petrography and geochemical characteristics of the basalt lava flows in Seongsan-Ilchulbong area, the easternpart of Jeju island, Korea, to understand the evolutionary processes of magma. Basalt lavas are classified into the Pyoseon-ri basalt and the Seongsan-ri basalt. The Pyoseon-ri basalt is dark-gray colored with many vescicles, and mainly consists of olivine, feldspar and rarely of clinopyroxene as phenocrysts. The Seongsan-ri basalt is largely aphanitic basalt and bright-gray colored, divided into two lava-flow units: lower lava flow (B1) and upper lava flow (B2) by the intercalated yellowish lapillistone and paleosol. The lavas plotted into sub-alkaline tholeiitic basalt and alkaline basalt series. The tholeiitic basalts have characteristically higher , and CaO contents, but lower and other incompatible elements compared to the alkali basalts. The tholeiitic basalts have higher to the same MgO contents than the alkalic basalts. The contents of Ni, Cr, and MgO show a strong positive correlation, which indicates that low-MgO phases like plagioclase and titanomagnetite were important during the differentiation of magma. The contents of incompatible elements against that of Th show a strong positive correlation. The chondrite-nomalized REE patterns of tholeiitic and alkalic basalts are subparallel each other. LREEs contents of the former are lower than, but HREEs contents are similar to the latter. They both are similar to their K/Ba ratios. The primitive-mantle normalized spider diagram demonstrates that the contents of Ba and Th of all basaltic magma are enriched, and yet Cr, Ni are depleted. The tholeiitic and alkalic basalts may be originated from a different degree of the partial melting of the same mantle material source, and one shows a higher degree of the partial melting than the other.

A Study on the Change of Magma Activity from 2002 to 2009 at Mt. Baekdusan using Surface Displacement

There have been a number of observed precursors of volcanic activities- such as volcanic earthquake, surface inflation, specific volcanic gas emission, temperature of hot spring- at Mt. Baekdusan since 2002. We identified the increase of the volume of magma chamber beneath Mt. Baekdusan as we observed an inflation trend of vertical and horizontal surface displacement around Cheonji caldera lake by using precise leveling data from 2002 to 2009. The surface displacement trend changed to deflation in 2010, and the trend changed to inflation again after a while. Utilizing the data of inflated surface (46.33 mm) on the northern slope of Mt. Baekdusan from 2002 to 2003, we calculated the volume change of magma chamber beneath the Mt. Baekdusan. The volume change was about 0.008 () from 2002 to 2003. It indicated that a new magma (0.008 ) injected to the magma chamber 5 km below Mt. Baekdusan.

A Preliminary Study for Predicting a Damage Range of Pyroclastic Flows, Lahars, and Volcanic Flood caused by Mt. Baekdusan Eruption

Products of the eruption of Mt. Baekdusan are identified as volcanic materials at the estuaries of the Songhuagang river to north, the Dumangang river to east and the Amnokgang river to west. More speficially, pyroclastic flows, lahars and volcanic floods can affect an area of 400km in radius, centering around Lake Cheonji caldera. However, unlike the millenium eruption, the flow situation has been changed. Because multi-purpose dams and reserviors with a combined pondage of mora than 2 billion tons of water have been built in the rivers of which sources are originated from Lake Cheonji caldera. In addition, the flow of fluids expected to take place when the volcano has erupted is thought to be affected by artificial constructions in both direct and indirect ways. This study calculates the direction of fluids flow by using numerical analyses of pyroclastic flows, lahars and volcanic floods that can occur when the volcano of Mt. Baekdusan has erupted. We also estimate the scope of damages by pyroclastic flows, lahars, volcanic flooding caused by the pondage of the dams and water storages in and around Mt. Baekdusan. Pyroclastic flows transported over the steep slopes at the early times of eruptions move over the mountain slopes, affecting airplanes, and lahars due to leaks of Lake Cheonji could reach as far as major rivers and streams near Mt. Baekdusan. Unlike historical accounts, volcanic flood is expected to be limited in its scope of influence to reservoirs bigger than Lake Cheonji in pondage.

TITAN2D Simulations of Pyroclastic Flows from Small Scale Eruption at Mt. Baekdusan

Many eruptions of Mt. Baekdusan volcano have been recorded in the historical literatures, and there were unrest precursors in 2002. Based on the geological survey results, it has been recognized that Mt. Baekdusan’s Plinian eruptions had caused ashfall, followed by the occurrence of pyroclastic flows, which were caused by the collapse of eruption column. Therefore, we simulated the range of the impacts of pyroclastic flows, which were caused by small eruptions from a specific crater. Based on the simulation results, it can be interpreted that, when the pyroclastic flows are caused by the eruption column collapse from an eruption with less than VEI 3, the impacts will range from the outer rim of the caldera to the mountain slope 7 km at the maximum distance. Furthermore, it is interpreted that, when the eruption column occurs by the crater located inside the caldera, most will be deposited inside the caldera and what overflows will be deposited thickly mostly in the north valley, the upper stream region of Erdaobaihe.