Nonlinear characteristics of super resolution chalcogenide thin film
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Nonlinear characteristics of super resolution chalcogenide thin film Se-Young Kim, Myung-jin Kang and Se-Young Choi Department of Ceramic Engineering, Yonsei University 134, Shinchon-Dong, Sudaemun-Ku, Seoul, 120-749, Korea ABSTRACT A third order nonlinear optical material, As2Se3 was proposed for super resolution near field structure disk. As2Se3 was deposited by thermal evaporation technique. Composition, phase, surface morphology, linear/non-linear optical properties were obtained from EPMA, XRD, AFM, UV-VIS-NIR spectrophotometer and VASE. As2Se3 thin film showed large non-linear optical characteristics (χR(3)=7.42×10-7m2/w, γ=1.268×10-5m2/w) and self-focusing phenomenon. Super resolution effects of the As2Se3 thin films were measured by using the laser beam profiler. As a result, recording density can be enhanced by 2.3 times, in case of 350nm As2Se3 thin film was deposited as super-RENS. INTRODUCTION A super-resolution near-field structure (super-RENS) is one of the candidates for increasing recording density by simply inserting a layer in the phase change disk without changing laser diodes and optical pick-up components. The super-RENS has the advantage of simpler recording head design, less mechanical damage, and higher recording speed than the conventional nearfield optical recording method [1]. 1st and 2nd generation super-RENS materials were Sb thin film and AgOx thin film layer [2,3]. Recently, PtOx thin film was reported as 3rd generation super-RENS which has huge carrier to noise ratio (CNR) [3-6]. In this work, As2Se3 was proposed as self-focusing type super-RENS materials that has superresolution effect with fast response time. Acioli et at. reported that the response time of nonresonant type third order non-linear optical materials is tens of pico second order [7]. On the other hand, Sb thin film takes about 20 ns to operate as super-RENS [8]. We measure the third nonlinear refractive index and non-linear absorption coefficient of the As2Se3 thin film. Selffocusing effect of As2Se3 thin film was observed by using laser beam profiler. EXPERIMENTAL PROCEDURE Chalcogenide glass was prepared with a 10g batch of arsenic (99.99%, Sterm chemicals, Japan) and selenium (99.99%, High purity chemicals, Japan). The batch was introduced into a quartz ampoule which were sealed under vacuum of 1×10-5torr. The sealed ampoule was melted at 800 for 24 hrs with using rocking furnace for homogenization of the melted liquid.
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Ampoule was quenched in air and chalcogenide glass was annealed at the temperature of Tg
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(176 ) that determined by using differential scanning calorimetry (STA-1500/DSC-SP, U.S.A.). As2Se3 thin films were deposited by thermal evaporation technique. The thermal evaporation process was carried out at a pressure of 5 × 10-6 torr with using tungsten boat. The deposition rate was about 5 /s. (100) Si wafer and slide glass were used as substrate. Phase and composition of target material and as deposited thin films were analyzed by X-ray diffraction (XRD, Rigaku, DMax, Japan) and
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