Bonghoon Kang

Thermal Evaporation of Amorphous Chalcogenide on Single-mode Optical Fiber

We made a film of a few µm thickness by evaporating As₂S₃ piece to perpendicularly cut optical fiber by thermal evaporation process. Linear refractive index(n) and linear absorption coefficient(k) of amorphous As₂S₃ are 2.525 and 1.727×10⁻³, respectively. A surface roughness did not exceed 2 ㎚ and a transmission spectrum showed that the sample of thermal evaporation was homogeneous.

Property Change of LiNbO3 Fabricated by Vapor Transport Equilibration Process

Congruent LiNbO3 crystal wafers were fabricated to be Li-compensated LiNbO3 by vapor transport equilibration process. The wavelength of absorption edge for Li-compensated LiNbO3 crystals is shift to shorter wavelength as the processing time increases. Through the P–E hysteresis loop, the coercive field of Li-compensated LiNbO3 was around 6–8 kV/mm. In non-critical phase matched second-harmonic generation, the phase matching temperature change as well as the birefringence change for temperature was measured. The phase matching temperature of Li-compensated LiNbO3 was observed around 230°C and the birefringence change for temperature was smaller than that of congruent LiNbO3.

Optical and Dielectric Properties of Reduced SrTiO₃ Single Crystals

The optical band gap energy for SrTiO₃ by reduction at high temperature was 3.15 eV. The reflectivity of reduced SrTiO₃ single crystals showed little variation, however, the reflectivity by the reduction condition had no effect. For the phonon mode at about 790 ㎝?¹, a blue-shift took place upon N₂ reduction and the decreased. However, a red-shift took place upon a H₂-N₂ reduction and the increased at the same phonon mode. With decreasing temperature the dielectric constant decreased rapidly. The thermal activation energies were 0.92-1.02 eV.

Dielectric Properties of SrxBa1-xNb2O6 Ceramics and Single Crystals

SrxBa1-xNb2O6 (SBN) ceramics were synthesized from Sr0.45Ba0.55Nb2O6 (45SBN) to 75SBN according to x content, and the mineral phases of ceramics were identified by XRD. Some SBN single crystals were grown by Czochralski method. There was only one single phase in from 45SBN to 70SBN when synthesizing at 1350 °C, but 75SBN ceramics had SrNb2O6 as second phase. The single crystal growth of SBN was generally difficult because of including bubbles, being black or poly-crystalline. This is considered to be related the properties of SBN ceramics synthesis as well as SBN melt. 60SBN and 75SBN single crystals have been grown in 4 cm Pt crucible with Pt wires as seed. And the crystals have grown to c-axis direction, and had some facets, which were identified.

Optimization of the Input Fundamental Beam by Using a Spatial Filter Consisting of Two Apertures

Second harmonic generation (SHG) is widely used in nonlinear optical spectroscopy. The optimization of the power efficiency of SHG is of primary importance in a number of applications, especially when continuous wave (cw) beams with relatively low peak power are frequency doubled. If the input light field is a Gaussian beam, the dynamics of SHG is determined by the power of the input beam, the spatial shape of the input beam, its confocal parameter, the Poynting vector walk-off length, the phase matching condition, and so on [1,2]. The existence of an optimum for the beam waist is the result of the best compromise between the beam focalization, which tends to increase the efficiency, and the diffractive spread, which tends to reduce the efficiency. In some previous paper, a Bessel beam could generate the second harmonic more efficiently than Gaussian beams because they propagate without any modification of the transverse intensity profile and, in this respect, they are ‘non-diffracting’ [3–5] . Beam shaping is a process whereby the irradiance of the laser beam is changed along its cross section. In order for beam shaping to be effective, it is necessary to be able to measure the degree to which the irradiance pattern or beam profile has been modified by the shaping medium.

Growth and physical properties of Sr x Ba 1-x Nb 2 O 6 (x

(60SBN) and (75SBN) single crystals were grown by Czochralski method. Growing direction was , and as-grown crystals has well-developed (001) plane. Temperature- and frequency dependence of dielectric constant represent relaxor ferroelectrics. 60SBN has wider optical transmittance than 75SBN.

Growth Properties of Tungsten-Bronze Sr 1-x Ba x Nb 2 O 6 Single Crystals

Abstract Tungsten bronze structure Sr 1-x Ba x Nb 2 O 6 (SBN) single crystals were grown primarily using the Czochralski method,in which several difficulties were encountered: striation formation and diameter control. Striation formation occurred mainlybecause of crystal rotation in an asymmetric thermal field and unsteady melt convection driven by thermal buoyancy forces.To optimize the growth conditions, bulk SBN crystals were grown in a furnace with resistance heating elements. The zone ofO 2 atmosphere for crystal growth is 9.0 cm and the difference of temperature between the melt and the top is 70 o C. Accordingto the growth conditions of the rotation rate, grown SBN became either polycrystalline or composed of single crystals. In thecase of as-grown Sr 1-X Ba X Nb 2 O 6 (x = 0.4; 60SBN) single crystals, the color of the crystals was transparent yellowish and thegrowth axis was the c-axis. The facets of the crystals were of various shapes. The length and diameter of the single crystalswas 50~70 mm and 5~10 mm, respectively. Tungsten bronze SBN growth is affected by the temperature profile and theatmosphere of the growing zone. The thermal expansion coefficients on heating and on cooling of the grown SBN singlecrystals were not matched. These coefficients were thought to influence the phase transition phenomena of SBN.Key wordstungsten bronze structure, Sr

Barium Nitrate Single Crystals Growth by Aqueous Solution Method

(Received November 22, 2012 : Received in revised form December 2, 2012 : Accepted December 3, 2012) Abstract The growing conditions of barium nitrate Ba(NO3)2 single crystals using the aqueous solution method have been studied. Supersaturation can be calculated by measuring the temperature of the solution and its equilibrium temperature. Supersaturation of Ba(NO3)2 was 0.7% at 32.0 o C and about 3% at 34.0 o C. The obtained single crystals have three kind of morphology: tetrahedral, cubic, and, rarely, dodecahedral. The normal growth rate is proportional to the supersaturation; it is necessary to make the solution below 5% supersaturation in order to obtain transparent Ba(NO3)2 single crystals. The normal growth rate for { } faces was 2.51 × 10 �6 mm/s for the 0.7% supersaturation condition (32.0 o C), 6.43 × 10 �6 mm/s for the the condition of 3.0% supersaturation, and 7.01 × 10 �6 mm/s for the condition of 5.0% supersaturation. The quality of the grown crystals depends on the nature of the seed, the cooling rate employed, and the agitation of the solution. The faces of the obtained crystals have been identified uising an X-ray diffractometer. The surface diffusion is responsible for the low growth rates of the { } faces.

Power Characteristics of cw Second-harmonic Generation in Periodically Poled LiNbO₃

We verified through a noncritical phase-matched second-harmonic generation experiment that the periodically-poled LiNbO₃ (PPLN) had a large effective nonlinear optical coefficient, demonstrating that the QPM grating was uniform throughout the entire length of PPLN. The quasi-phase matching temperature was 193.4℃. The maximum SHG output power at the fundamental power of 2.0 W was found to be 18.0 mW; generated second-harmonic beam was found to have no photorefractive effect.

Study on Poling of LiNbO 3 Fiber Single Crystals

Congruent or stoichiometric LiNbO₃ fiber single crystals were grown by the μ-PD method, and the grown fiber crystals have the several (2 or 3) ridges with a diameter of 1.35~1.5 ㎜ and a length of 40~100 ㎜. In this μ-PD process, different growth rates (10~60 ㎜/h) were applied. Pt wire or LiNbO₃ crystal was used as a seed. The properties of grown LiNbO₃ fiber single crystals having a-axis or c-axis according to seeds were effected by the grown conditions(Pt tube diameter, pulling speed, after heater etc.). Disk-type LiNbO₃ samples were poled in condition of DC 5 V/㎝ at 1050, 1075 or 1100℃. XRD, SEM, conoscope image through the polarized microscope, TC measuring apparatus, optical transmittance measuring instrument are used to identify the properties of LiNbO₃.