Structural evolution and second harmonic properties of lithium niobate-tantalate nanocrystals embedded in a borate glass

Nano-crystals of LiNbxTa1 (-) O-x(3) were evolved by subjecting melt-quenched 1.5Li(2)O-2B(2)O(3)-xNb(2)O(5)-(1 - x)Ta2O5 glasses (where x = 0, 0.25, 0.5, 0.75 and 1.00) to a controlled 3-h isothermal heat treatment between 530 and 560 degrees C. Detailed X-ray diffraction and Raman spectral studies confirmed the formation of nano-crystalline LiNbxTa1 (-) O-x(3) along with a minor phase of ferroelectric and non-linear optic Li2B4O7. The sizes of the nanocrystals evolved in the glass were in the range of 19-37 nm for x = 0-0.75 and 23-45 nm for x = 1.00. Electron microscopic studies confirmed a transformation of the morphology of the nano-crystallites from dendritic star-shaped spherulites for x = 0 to rod-shaped structures for x = 1.00 brought about by a coalescence of crystallites. Broad Maker-fringe patterns (recorded at 532 nm) were obtained by subjecting the heat-treated glass plates to 1064 nm fundamental radiation. However, an effective second order non-linear optic coefficient, d(eff), of 0.45 pm/V, which is nearly 1.2 times the d(36) of KDP single crystal, was obtained for a 560 degrees C/3 h heat-treated glass of the representative composition x = 0.50 comprising 37 nm sized crystallites. (C) 2015 Elsevier B.V. All rights reserved.

Schottky barrier heights of tantalum oxide, barium strontium titanate, lead titanate, and strontium bismuth tantalate

The Schottky barrier heights of various metals on the high permitivity oxides tantalum pentoxide, barium strontium titanate, lead zirconate titanate, and strontium bismuth tantalate have been calculated as a function of the metal work function. It is found that these oxides have a dimensionless Schottky barrier pinning factor S of 0.28-0.4 and not close to 1 because S is controlled by Ti-O-type bonds not Sr-O-type bonds, as assumed in earlier work. The band offsets on silicon are asymmetric with a much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate are relatively poor barriers to electrons on Si. © 1999 American Institute of Physics.

Schottky barrier heights of tantalum oxide, barium strontium titanate, lead zirconate titanate and strontium bismuth tantalate

Schottky barrier heights of various metals on tantalum pentoxide, barium strontium titanate, lead zirconate-titanate and strontium bismuth tantalate have been calculated as a function of metal work function. These oxides have a dimensionless Schottky barrier pinning factor, S, of 0.28 - 0.4 and not close to 1, because S is controlled by the Ti-O type bonds not Sr-O type bonds, as assumed previously. Band offsets on silicon are asymmetric with much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate (BST) are relatively poor barriers to electrons on Si.

Bismuth-activated luminescent materials for broadband optical amplifier in WDM system

New broadband near infrared luminescence covering the whole work windows (1260-1625 nm) of the current wavelength division multiplexing (WDM) system was found from bismuth-activated M2O-Al2O3-SiO2 (M = Li, Na) and Li2O-Ta2O5-SiO2 glasses at room temperature in the case of 808 nm-laser excitation. But the near infrared luminescence mechanism of the bismuth-activated glasses is not well understood up to now. The figure-of-merits of bandwidth and gain of the glasses are better than those of Er3+-doped silicate glasses and Ti3+ doped sapphire, implying they are the promising gain-medium candidates for the broadband amplifiers and the widely tunable laser sources. (c) 2007 Elsevier B.V. All rights reserved.

飞秒脉冲激光器中色散补偿膜的设计

阐述了用光学薄膜进行色散补偿的基本原理，介绍了设计的基本过程．根据Ti：Sapphire飞秒激光器中腔内色散补偿的要求，设定了色散补偿目标，通过计算机优化，得到了一种40层的Ta2O5／SiO2介质膜系．该膜系能在720～870am范围获得大于99．5％的反射率，在510～550nm获得大于90％的透射率，在740～850nm提供较平滑的-40fs^2的群延迟色散．这样的结果经过7次反射后，可以补偿5-mm Ti：sapphire晶体产生的绝大部分群延迟色散。

重复率激光作用下光学薄膜损伤的累积效应

使用脉宽12ns，频率10Hz的1064nm调Q Nd：YAG激光器，研究了高反射膜在重复率激光作用下的损伤的累积效应。实验发现，高反射膜的损伤阈值随辐照脉冲数增加而降低，表现出明显的累积效应。通过对损伤阈值和损伤概率以及辐照次数的统计性研究．并结合单脉冲辐照的结果，说明了存在于薄膜中微小的缺陷参与了多脉冲激光对薄膜的损伤过程。可用预损伤机制解释实验结果。得到了关于IBS制备的高反射膜的损伤阈值和照射次数的关系式，并用实验结果进行验证．发现具有很好的一致性。实验过程中样品的损伤形貌通过Nomarski偏光

多脉冲激光作用下光学薄膜损伤的累积效应

研究了高反射膜在多脉冲激光作用下损伤的累积效应．实验中使用1064nm调Q的Nd：YAG激光器，脉宽是12ns，频率为10Hz．实验发现：高反射膜的损伤阈值随辐照脉冲数增加而降低，表现出明显的累积效应．通过对损伤阈值和损伤概率以及辐照次数的统计性研究，并结合单脉冲辐照的结果，说明了存在于薄膜中微小的缺陷参与了多脉冲激光对薄膜的损伤过程，得到了制备IBS高反射膜的损伤闽值和照射次数的关系式，用Nomarski偏光显微镜观察了实验过程中样品的损伤形貌，发现是典型的缺陷损伤．

窄带干涉滤光片抗击不同输出方式激光的损伤特性研究

利用Nd：YAG调Q单脉冲激光和自由脉冲激光对硬膜窄带干涉滤光片进行激光损伤阈值的测试，并且采用表面热透镜技术测量了滤光片的吸收率。实验发现：窄带干涉滤光片的吸收率和激光损伤阈值强烈依赖于辐照激光波长与窄带干涉滤光片通带的相对位置；在调Q单脉冲激光作用下，不同中心波长的滤光片损伤形貌存在明显的差别，而在自由脉冲激光作用下，各滤光片的损伤形貌则趋于相同．均表现为典型的热熔烧蚀破坏。根据实验结果，结合损伤形貌，通过驻波场理论对激光作用下滤光片内电场分布的分析与模拟．探讨了两种激光模式作用下滤光片的损伤特征和损

Influence of vacuum organic contaminations on laser-induced damage of 1064 nm anti-reflective coatings

We investigate the influence of vacuum organic contaminations on laser-induced damage threshold (LIDT) of optical coatings. Anti-reflective (AR) coatings at 1064 nm made by Ta2O5/SiO2 are deposited by the ion beam sputtering method. The LIDTs of AR coatings are measured in vacuum and in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5 J/cm(2) in air to 15.7 J/cm(2) in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.

High temperature annealing effect on structure, optical property and laser-induced damage threshold of Ta2O5 films

Ta2O5 films were deposited by conventional electron beam evaporation method and then annealed in air at different temperature from 873 to 1273 K. It was found that the film structure changed from amorphous phase to hexagonal phase when annealed at 1073 K, then transformed to orthorhombic phase after annealed at 1273 K. The transmittance was improved after annealed at 873 K, and it decreased as the annealing temperature increased further. The total integrated scattering (TIS) tests and AFM results showed that both scattering and root mean square (RMS) roughness of films increased with the annealing temperature increasing. X-ray photoelectron spectroscopy (XPS) analysis showed that the film obtained better stoichiometry and the O/Ta ratio increased to 2.50 after annealing. It was found that the laser-induced damage threshold (LIDT) increased to the maximum when annealed at 873 K, while it decreased when the annealing temperature increased further. Detailed damaged models dominated by different parameters during annealing were discussed. (C) 2008 Elsevier B. V. All rights reserved.

Influence of SiO2 additional layers on the laser induced damage threshold of Ta2O5 films

A series or Ta2O5 films with different SiO2 additional layers including overcoat, undercoat and interlayer was prepared by electron beam evaporation under the same deposition process. Absorption of samples was measured using the surface thermal lensing (STL) technique. The electric field distributions of the samples were theoretical predicted using thin film design software (TFCalc). The laser induced damage threshold (LIDT) was assessed using an Nd:YAG laser operating at 1064 nm with a pulse length of 12 ns. It was found that SiO2 additional layers resulted in a slight increase of the absorption, whereas they exerted little influence on the microdefects. The electric field distribution among the samples was unchanged by adding an SiO2 overcoat and undercoat, yet was changed by adding an interlayer. SiO2 undercoat. The interlayer improved the LIDT greatly, whereas the SiO2 overcoat had little effect on the LIDT. (C) 2007 Elsevier Ltd. All rights reserved.

Blue-green optically pumped GaN-based vertical cavity surface emitting laser

Blue-green GaN-based vertical cavity surface emitting lasers (VCSELs) were fabricated with two dielectric Ta2O5/SiO2 distributed Bragg reflectors. Lasing action was observed at a wavelength of 498.8 nm at room temperature under optical pumping. Threshold energy density and emission linewidth were 189 mJ/cm(2) and 0.15 nm, respectively. The result demonstrates that blue-green VCSELs can be realised using III-nitride semiconductors.

Blue-violet Lasing of Optically Pumped GaN-Based Vertical Cavity Surface-Emitting Laser With Dielectric Distributed Bragg Reflectors

Optically pumped GaN-based vertical cavity surface-emitting laser (VCSEL) with two Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs) was fabricated via a simplifled procedure direct deposition of the top DBR onto the GaN surface exposed after substrate removal and no use of etching and polishing processes. Blue-violet lasing action was observed at a wavelength of 397.3 ran under optical pumping at room temperature with a threshold pumping energy density of about 71.5 mJ/cm(2). The laser action was further confirmed by a narrow emission linewidth of 0.13 nm and a degree of polarization of about 65%. The result suggests that practical blue-violet GaN-bsaed VCSEL can be realized by optimizing the laser lift-off technique for substrate removal.

SiO2/Ta interface reaction in magnetic multilayers and its influence on Ta buffer layers

Ta is often used as a buffer layer in magnetic multilayers. In this study, Ta/Ni81Fe19/Ta multilayers were deposited by magnetron sputtering on sing-crystal Si with a 300-nm-thick SiO2 film. The composition and chemical states at the interface region of SiO2/Ta were studied using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is an 'inter-mixing layer" at the SiO2/Ta interface due to a thermodynamically favorable reaction: 15 SiO2 + 37 Ta = 6 Ta2O5 + 5 Ta5Si3. Therefore, the Ta buffer layer thickness used to induce NiFe (111) texture increases.

Magnetic property and interface structure of Ta/NiO/NiFe/Ta

Ta/NiO/NiFe/Ta multilayers, utilizing Ta as buffer layer, were prepared by rf reactive and de magnetron sputtering. The exchange coupling field between NiO and NiFe reached a maximum value of 9.6x10(3) A/m at a NiO film thickness of 50 nm. The composition and chemical states at interface region of Ta/NiO/Ta were studied by using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is an "intermixing layer" at the Ta/NiO land NiO/Ta) interface due to a thermodynamically favorable reaction 2Ta + 5NiO = 5Ni + Ta2O5. This interface reaction has a great effect on exchange coupling. The thickness of Ni+NiO estimated by XPS depth. profiles is about 8-10 nm.