Power delivery of free electron laser light by hollow glass waveguides

Hollow glass waveguides are used to deliver free electron laser (FEL) energy for applications in medicine and laser surgery. The hollow guides, optimized for the delivery of 6.45-μm FEL radiation, exhibited losses for the 1000-μm bore as low as 0.39 dB/m when the guide was straight and 1.75 dB/m when bent to a radius of 25 cm. Hollow glass guides are flexible, and their broadband capability provides an ideal fiber optic for the tunable FEL.     

High-peak-power, pulsed CO(2) laser light delivery by hollow glass waveguides

Flexible hollow glass waveguides with internal metallic and dielectric coatings have been used to deliver high-peak-power transversely excited atmosphere CO(2) laser energy. The straight guide loss is as low as 0.17 dB/m for 1000-mum-bore guides and 0.46 dB/m for 530-mum-bore guides propagating the HE(11) mode. The loss increases to 0.93 and 1.36 dB/m, respectively, when guides are bent to a radius of 0.25 m. The hollow glass waveguides have been used to deliver pulsed CO(2) laser energy successfully with a peak power of 0.7 MW and an energy of 350 mJ per pulse with a gas purge through the hollow core. The delivered average power is as high as 27 W. It is concluded that these waveguides are promising candidates for pulsed CO(2) laser delivery in medical and surgical applications.     

Optical transmission of hollow glass photonic-crystal fibers

A photonic-crystal fiber (PCF) with a forbidden photon band (FPB) in the visible spectral range has been created for the first time. The PCF shell comprises concentric layers of hollow circular air-filled channels with variable diameters. The optical transmission of the proposed PCF and the influence of the geometric parameters on the FPB width and position in the visible spectral range have been studied. By varying the PCF structure and geometry, it is possible to change the FPB characteristics, which offers broad possibilities of output light control.     

Antireflection coating formed by plasma-enhanced chemical-vapor deposition for terahertz-frequency germanium optics

A method of manufacturing optical coatings for germanium optics used at terahertz frequencies has been developed. The various optical coatings used at terahertz frequencies are difficult to manufacture conventionally because these coatings must be as thick as several tens of micrometers, which is far thicker than those used in the optical region. One way to overcome this problem is to form a silicon oxide layer through plasma-enhanced chemical-vapor deposition, with silane (SiH4) as a source gas. Using this method, I formed 21-microm-thick silicon oxide films as antireflection (AR) layers for germanium optics and obtained low reflection at 1.7 THz (wavelength, lambda = 175 microm). This method is easily applied to large-aperture optics and micro-optics as well as to optics with a complex surface form. The AR coatings can also be formed for photoconductive detectors made from germanium doped with gallium at a low temperature (160 degrees C); this low temperature ensures that the doped impurities in the germanium do not diffuse. Fabrication of optical coatings upon substrates that have refractive indices of 3.84-11.7 may also be possible by control of the refractive indices of the deposited layers.     

CuZr-based bulk metallic glass and glass matrix composites fabricated by selective laser melting

Monolithic bulk metallic glass and glass matrix composites with a relative density above 98 ％ were produced by processing Cu46Zr46Al8 (at.％) via selective laser melting (SLM).Their microstructures and mechanical properties were systematically examined.B2 CuZr nanocrystals (30-100 nm in diameter) are uniformly dispersed in the glassy matrix when SLM is conducted at an intermediate energy input.These B2 CuZr nanocrystals nucleate the oxygen-stabilized big cube phase during a remelting step.The presence of these nanocrystals increases the structural heterogeneity as indirectly revealed by mircrohardness and nanoindentation measurements.The corresponding maps in combination with calorimetric data indicate that the glassy phase is altered by the processing conditions.Despite the formation of crystals and a high overall free volume content,all additively manufactured samples fail at lower stress than the as-cast glass and without any plastic strain.The inherent brittleness is attributed to the presence of relatively large pores and the increased oxygen content after selective laser melting.     

Characterization of borophosphosilicate glass soot fabricated by flame hydrolysis deposition for silica-on-silicon device applications

The use of flame hydrolysis deposition (FHD) to fabricate porous silica glass soot in the B₂O₃-P₂O₅-SiO₂ glass system (BPSG) is described for silica-on-silicon device applications. The deposition conditions with a Si substrate temperature (200 °C) and a flame temperature (1300–1500 °C) are appropriate to synthesize the SiO₂ and P₂O₅-SiO₂ non-crystalline glass soot. However, further investigations for the B₂O₃-P₂O₅-SiO₂ glass soot are needed to obtain complete amorphous phases. The densification process of porous silica glass soot in the three systems of SiO₂, P₂O₅-SiO₂ and B₂O₃-P₂O₅-SiO₂ is also described to estimate the onset of sintering temperature. The OH absorption measurements are performed to try to identify incorporation of hydroxyl contaminants in the systems of P₂O₅-SiO₂ and B₂O₃-P₂O₅-SiO₂.     

Bismuth activated alumosilicate optical fibers fabricated by surface-plasma chemical vapor deposition technology

Plasma chemical technology is experimentally applied to the fabrication of a Bi-activated alumosilicate-core pure-silica-cladding fiber preform. To the best of our knowledge, this is the first time this technology has been applied in this way. We measure gain efficiency at pumping by a 1058 nm wavelength Yb fiber laser in a piece of a newly obtained fiber 20 m in length within 100-1200 nm wavelengths band. The gain efficiency reaches as high as 0.2 dB/mW. Bi-activated alumosilicate-core pure-silica-cladding fiber that is not more than 12 m in length serves a basis for a 1 W output power fiber laser emitting at the wavelength of 1160 nm with 8% slope efficiency. We also measure the photoluminescence spectrum and kinetics of Bi centers responsible for laser emission under the excitation of 193 nm wavelength ArF laser pulses.     

Origin of microinhomogeneities in As-S-Se glass fibers fabricated by the double-crucible method

The optical losses in sulfoselenide glass fibers fabricated by the double-crucible method are shown to rise in going from the first-drawn portion to the back end of the fiber. Optical microscopy, IR and Raman spectroscopy, energy-dispersive x-ray microanalysis, and differential scanning calorimetry data indicate that fiber drawing is accompanied by the development of microinhomogeneities of the chemical and phase compositions of the melt, which are responsible for the increased scattering losses. The microinhomogeneities originate from phase segregation of the molten glass.     

Penetration of high-intensity Er:YAG laser light emitted by IR hollow optical fibers with sealing caps in water

The penetration depth in water was measured for Er:YAG laser light in a high density relevant to clinical applications. Various types of focusing elements were used to guide the light efficiently. We found that the transmission distance depended strongly on the beam shape in the water. When we used a plano-convex type of focusing cap, the penetration depth was larger than that when a dome- or ball-type cap were used.     

Microstructure and properties of tungsten heavy alloys fabricated by laser direct deposition

In this paper, tungsten heavy alloys (THAs) were fabricated by laser direct deposition technology. The phase composition, microstructure and the influences of Fe and Co content on the properties of THAs were investigated. The results showed that the laser deposition layers were composed by W, Ni₄W and Ni, fine and dense columnar crystals were distributed between non-melting W particles. The direction of crystals growth nearly paralleled the deposition direction at the bottom of deposition layers and nearly paralleled the scanning direction at the top. Both Fe and Co could increase the tensile strength of THAs and the elongation of W–Ni–Co alloys was higher than W–Ni–Fe alloys.     

PLD法制备ZnO/Si异质结的I-V特性研究

用脉冲激光沉积法分别在不同电阻率的p型和n型Si( 100)衬底上制备了不掺杂ZnO薄膜,相应制成n-ZnO/p-Si和n-ZnO/n-Si异质结器件.利用X射线衍射和原子力显微镜对ZnO薄膜进行的结构和形貌测试表明,薄膜结晶情况良好,具有高度的c轴择优取向,表面颗粒大小、分布均匀.对器件的I-V特性测试表明,在无光条件下,制备的n-ZnO/p-Si异质结漏电流很低,而n-ZnO/n-Si同型异质结漏电流要稍大一些;随衬底电阻率的增大,上述器件的阈值电压变小;器件在光照下的漏电流明显比无光条件下的要大.     

Ultrathin Al-doped transparent conducting zinc oxide films fabricated by pulsed laser deposition

Al-doped transparent conducting zinc oxide (AZO) films, approximately 20-110 nm-thick, were deposited on glass substrates at substrate temperatures between 200 and 300 °C by pulsed laser deposition (PLD) using an ArF excimer laser (λ = 193 nm). When fabricated at a substrate temperature of 260 °C, a 40-nm-thick AZO film showed a low resistivity of 2.61 × 10^− 4 Ω·cm, carrier concentration of 8.64 × 10²⁰ cm^− 3, and Hall mobility of 27.7 cm²/V·s. Furthermore, for an ultrathin 20-nm-thick film, a resistivity of 3.91 × 10^− 4 Ω·cm, carrier concentration of 7.14 × 10²⁰ cm^− 3, and Hall mobility of 22.4 cm²/V·s were obtained. X-ray diffraction (XRD) spectra, obtained by the θ-2θ method, of the AZO films grown at a substrate temperature of 260 °C showed that the diffraction peak of the ZnO (0002) plane increased as the film thickness increased from 20 to 110 nm. The full-width-at-half-maximum (FWHM) values were 0.5500°, 0.3845°, and 0.2979° for film thicknesses of 20, 40, and 110 nm, respectively. For these films, the values of the average transmittance in visible light wavelengths (400-700 nm) were 95.1%, 94.2%, and 96.6%, respectively. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) observations showed that even the 20-nm-thick films did not show island structures. In addition, exfoliated areas or vacant and void spaces were not observed for any of the films.     

静态化学气相沉积法制备SiC纤维的拉伸强度分布研究

以沥青基炭单丝为基体,一甲基三氯硅烷为前驱体,使用静态化学气相沉积工艺,在1473K,常压环境下制备了SiC纤维.使用电子万能试验机测试了同一批次纤维的拉伸强度,结果表明其为双峰直方图分布.使用光学显微镜和扫描电子显微镜对纤维的形貌结构进行了表征.沿着反应器方向,不同区域的纤维依次表现为颗粒状、球状、平滑和倒圆锥结构.这些结构的差别导致了纤维力学强度的双峰分布.对沉积机制的分析表明,物料损耗效应和反应器两端的流场稳定性是影响纤维结构的主要因素.     

沉积位置对脉冲激光沉积纳米Si晶薄膜微观结构的影响

在4.0×10-4Pa的真空条件下,采用脉冲激光烧蚀技术在单晶Si衬底和石英衬底上制备了非晶纳米Si薄膜.在N2气氛下,经过900℃热退火得到纳米Si晶薄膜.采用表面台阶测试仪、扫描电子显微镜、拉曼光谱仪等检测手段对样品不同位置的微观结构进行了表征.测量结果表明制备的纳米Si晶薄膜厚度及其晶粒尺寸分布不均匀,随着测量点与样品沉积中心距离的增加,薄膜的厚度逐渐减小,纳米Si晶粒的尺寸逐渐增大.从脉冲激光烧蚀动力学的角度对实验结果进行了定性的分析.     

Silver-doped germanium sulphide glass channel waveguides fabricated by chemical vapour deposition and photo-dissolution process

Germanium sulphide glass thin films have been fabricated by chemical vapour deposition directly on commercial glass substrates. Silver (Ag)-doped channel waveguide structures were then prepared in a three step process, first channels were patterned in photo-resist, next a Ag thin film was deposited on the patterned waveguide by thermal evaporation, and finally the silver ions were doped into germanium sulphide glass by a photo-dissolution process. The refractive index of germanium sulphide increased by about 0.02 through the photo-dissolution process. The loss of the channel waveguides measured at 632.8 nm was 0.63 ± 0.05 dB/cm.     

Plastic deformation of a Zr-based bulk metallic glass fabricated by selective laser melting

Fully amorphous Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa and a reproducible plastic strain of about 0.5% were obtained for cylindrical SLM samples.The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass.This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation.Despite these heterogeneities,the shear bands are straight and form in the plane of maximum shear stress.Additive manufacturing,hence,might not only allow for producing large BMG samples with complex geometries but also for manipulating their deformation behaviour through tailoring porosity and structural heterogeneity.     

基于SVR的脉冲激光沉积TiN/AlN多层薄膜的工艺优化

根据脉冲激光沉积(PLD)法在单晶Si试样表面沉积制备多层TiN/AlN硬质膜实验数据,应用基于粒子群算法(PSO)寻优的支持向量回归(SVR)方法,建立不同工艺参数下沉积的TiN/AlN多层膜的AlN膜厚及TiN薄膜硬度的SVR预测模型。在相同的训练与测试样本集下,将SVR所得的AlN膜厚预测值与免疫径向基函数(IRBF)神经网络的计算结果进行比较。结果表明,SVR模型训练和预测结果的平均绝对百分误差要比IRBFNN模型的小,其预测精度更高,预测效果更好。应用SVR的TiN薄膜硬度模型对PLD法沉积TiN薄膜的工艺参数进行了优化,分析了多因素对PLD法沉积TiN薄膜硬度的交互作用和影响。该方法可为人们利用PLD法沉积TiN/AlN多层功能薄膜提供科学的理论指导,具有重要的理论意义和实用价值。     

Factors influencing the deposition of hydroxyapatite coating onto hollow glass microspheres

Hydroxyapatite (HA) and HA coated microcarriers for cell culture and delivery have attracted more attention recently, owing to the rapid progress in the field of tissue engineering. In this research, a dense and uniform HA coating with the thickness of about 2 μm was successfully deposited on hollow glass microspheres (HGM) by biomimetic process. The influences of SBF concentration, immersion time, solid/liquid ratio and activation of HGM on the deposition rate and coating characteristics were discussed. X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR) analyses revealed that the deposited HA is poorly crystalline. The thickness of HA coating showed almost no increase after immersion in 1.5SBF for more than 15 days with the solid/liquid ratio of 1:150. At the same time, SBF concentration, solid/liquid ratio and activation treatment played vital roles in the formation of HA coating on HGM. This poorly crystallized HA coated HGM could have potential use as microcarrier for cell culture.     

Large-sized-mismatched group-V element doped ZnO films fabricated on silicon substrates by pulsed laser deposition

Pulsed laser deposition has been utilized to synthesize impurity-doped ZnO thin films on silicon substrate. Large-sized-mismatched group-V elements (A^V) including P, As, Sb and Bi were used as dopants. Hall effect measurements show that hole concentration in the order of 10¹⁶-10¹⁸ cm⁻³, resistivity in the range of 10-100 Ω cm, Hall mobility in the range of 10-100 cm²/Vs were obtained only for ZnO:As and ZnO:Bi thin films. X-ray diffraction measurements reveal that the films possess polycrystallinity or nanocrystallinity with ZnO (002) preferred orientation. Guided by X-ray photoemission spectroscopy analyses and theoretical calculations for large-sized-mismatched group-V dopant in ZnO, the A_Zn^V-2V_Zn complexes are believed to be the most possible acceptors in the p-type A^V-doped ZnO thin films.     

Crack restriction mechanism of thin wall metal parts fabricated by laser direct deposition shaping

In order to restrict the generation and propagation of cracks in thin wall metal parts fabricated by laser direct deposition shaping method, using ‘element birth and death’ technique, a three-dimensional multitrack and multilayer thin wall model was developed, and the deposition process was simulated. Different scanning methods, including long edge parallel reciprocating scanning, short edge parallel reciprocating scanning and interlayer orthogonal parallel reciprocating scanning, were introduced. The effects of different substrate preheating temperatures were also researched. The von Mises equivalent stress and its X-, Y- and Z-directional principal stresses were analysed in detail. Under the same conditions used in the simulations, the deposition experiments were conducted, and the crack generation and restriction mechanism of thin wall metal parts were further discussed.