水热法生长复合钛宝石激光晶体

水热法生长了复合钛宝石(Al₂O₃/Ti:Al₂O₃)激光晶体.对外层Al₂O₃X射线ω扫描表明其晶体质量很高.外层生长的Al₂O₃和内部的钛宝石激光棒结合牢固、紧密,因而能适应高强度泵浦所带来的激光介质内部的热应力.复合激光晶体界面层带来的光损耗很小.就我们所知,这是首次用水热法生长复合激光晶体.     

Continuous-wave lasing at 1.06 μm in femtosecond laser written Nd:KGW waveguides

We report on the buried channel waveguide laser at 1065 nm in Nd:KGW waveguides fabricated by femtosecond laser writing with dual-line approach. A relatively high scanning speed of 0.5 mm/s enables acceptable propagation loss less than 2 dB/cm. The fluorescence emission spectra of Nd³⁺ ions measured shows that the fluorescence properties were well preserved in the waveguide region. A stable continuous wave laser at 1065 nm has been obtained at room temperature in the buried channel waveguides by optical pumping at 808 nm. A maximum output power of 33 mW and a slope efficiency of 52.3% were achieved in the Nd:KGW waveguide laser system.     

钛宝石泵浦Cr,Nd:YAG微片的自调Q激光特性

用连续的钛宝石激光泵浦１mm厚的Cr^4 ,Nd^3 ;YAG晶体微片获得了１．０６４μm的自调Ｑ激光输出,输出的激光调Ｑ脉冲非常稳定,泵浦的阈值功率为３０mW,脉冲宽度为１００ns随着泵浦功率的变化,脉冲宽度保持不变,而重复率则在变化。斜率效率随着输出耦合镜透过度的变化而变化,当输出耦合率为５％时,斜率效率高20%.一研究有助于进一步发展激光二极管泵浦的全固化的自调Ｑ微片激光器。     

超宽谱钛宝石飞秒激光器的研究进展

超宽谱钛宝石飞秒激光器的出现是近年来飞秒激光技术的重要进展之一.文章对近年来国际上出现的几种主要的钛宝石超宽谱飞秒激光器的原理、结构及优缺点进行了介绍,给出了其发展趋势.     

钛合金表面宽带激光熔覆梯度生物陶瓷复合涂层

为了减少激光熔覆过程中基材与生物陶瓷涂层之间的热应力,设计了一种梯度生物陶瓷复合涂层并采用宽带激光熔覆技术在Ti-6Al-4V合金上制备了梯度生物陶瓷复合涂层,对其组织和显微硬度进行了研究。结果表明：钙和氧元素主要分布在生物陶瓷涂层中;钛和钒元素主要分布在基材和合金化层内;磷元素分布在合金层与陶瓷层中。合金层中基底组织上分布着白色共晶组织和白色颗粒,基底组织主要为Ti(Al、P、Fe、V)相,白色共晶组织主要为Fe2Ti4O AlV3,白色颗粒为结晶析出的Al3V0.333 Ti0．666;生物陶瓷层中的基底组织为胞状晶,其上分布有灰色相和白色颗粒相,胞状晶主要为CaO、CaTiO3和HA,灰色相为β-TCP及Ca2Ti2O6,白色颗粒相为TiO2。合金层的最高硬度为1600Hv0．2,生物陶瓷涂层显微硬度最大值约为1300Hv0．2。     

Surface modification of cp-Ti using femtosecond laser micromachining and the deposition of Ca/P layer

Femtosecond laser processing is employed to create regular patterns and bioactive layer on the surface of pure titanium. Surface morphology and microstructure of the laser-processed layer are characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the processing with varied laser energies builds a surface with three-order roughness from nanometer scale to micrometer scale. Selected area electron diffraction indicates that some kind of TiO layer emerges on the surface after femtosecond laser machining. The bioactivity of TiO layer is further evaluated by soaking it in simulated body fluid (SBF). SEM observation and EDX analysis show that Ca/P layer is rapidly formed on the surface of TiO layer after SBF soaking. It implies that TiO layer with unique three-order roughness has good bioactivity.     

泡生法生长掺碳钛宝石激光晶体的研究

钛宝石激光晶体在现代高功率激光领域具有重要的应用价值, 但大尺寸、高品质的晶体生长仍是当前钛宝石应用面临的重大难题. 本文研究了泡生法技术生长大尺寸掺碳钛宝石激光晶体, 结果显示, 泡生法生长得到的直径180 mm、30 kg的钛宝石没有出现应力集中的开裂等宏观缺陷现象, 钛离子在晶体中分布均匀接近理论值, 晶体的FOM值达到200. 该研究对低红外残余吸收, 高品质因素、大尺寸钛宝石激光晶体的生长应用具有重要的现实意义.     

Second harmonic generation of pseudo mode-locked multi ten milliwatt picosecond Ti:sapphire laser

We report the single-pass second harmonic generation (SHG) of the picosecond Ti:sapphire laser with a periodically poled lithium niobate (PPLN) waveguide. We demonstrate a conversion efficiency of 37% for the 9-mW fundamental input power at 820 nm. This laser source can provide three types of pulsed modes such as picosecond, nanosecond, and contiuous wave, by adjusting the power of the pumping source. We compare the conversion efficiency in each mode, and clearly show that SHG efficiency depends on the pulsewidth, that is, the peak power of the laser source. As the temperature of the PPLN rises, the fundamental wavelength for phase-matching becomes longer. We indicate that the rate is about 0.06 nm/K.     

Second harmonic generation of pseudo mode-locked multi ten milliwatt picosecond Ti:sapphire laser

We report the single-pass second harmonic generation (SHG) of the picosecond Ti:sapphire laser with a periodically poled lithium niobate (PPLN) waveguide. We demonstrate a conversion efficiency of 37% for the 9-mW fundamental input power at 820 nm. This laser source can provide three types of pulsed modes such as picosecond, nanosecond, and contiuous wave, by adjusting the power of the pumping source. We compare the conversion efficiency in each mode, and clearly show that SHG efficiency depends on the pulsewidth, that is, the peak power of the laser source. As the temperature of the PPLN rises, the fundamental wavelength for phase-matching becomes longer. We indicate that the rate is about 0.06 nm/K.     

Novel synthesis method of YAG: Ce micron-sized powders and its luminescence properties

Micron-sized Ce-doped yttrium aluminum garnet (YAG: Ce³⁺) powders are synthesized successfully by a new method including three processes including solvothermal treatment, precursor preheated and annealing treatment in a mild condition. The phase, morphology and luminescent properties are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation (PLE) and photoluminescence (PL) spectra respectively. The single-phase sample can be formed after solvothermal treatment at 180 °C for 12 h and annealing at 1200 °C for 4 h. The results obtained by SEM show that the particles with narrow size distribution (∼4 μm) and nice morphology are formed after annealing treatment. This indicates that it has good homogeneity and dispersion. The micron-sized Ce-doped YAG shows broad emission bands in the range of 500–680 nm with the maximum intensity at 577 nm.     

Ti6Al4V合金激光原位合成自润滑复合涂层高温摩擦学性能

为提高Ti6Al4V合金的高温摩擦学性能,采用激光熔覆技术在其表面原位合成多相混杂金属基高温自润滑耐磨复合涂层,熔覆粉末的成分为Ni60-16.8%TiC-23.2%WS_2(质量分数,下同),系统地研究复合涂层的显微组织、物相结构及其在20,300,600,800℃下的摩擦学性能和相关磨损机理。结果表明:复合涂层的显微硬度(701.88HV_0.5)约为基体(350 HV_0.5)的2倍;由于原位合成固体润滑相(Ti_2SC/TiS/NiS/TiO/TiO_2/NiCr_2O_4/Cr_2O_3)和硬质相(W,Ti)C_1-x/TiC/Cr_7C_3的协同作用,复合涂层的耐磨减摩性能明显优于基体。随着温度升高,涂层和基体的摩擦因数和磨损率均呈下降趋势,在800℃时复合涂层和基体的摩擦因数分别为0.32和0.43,磨损率分别为1.80×10^-4,2.92×10^-5mm/Nm。在800℃下塑性变形、分层和氧化磨损为基体主要磨损机理,复合涂层以氧化磨损和轻微的黏着磨损为主。     

Effect of boron incorporation on the structure and electrical properties of diamond-like carbon films deposited by femtosecond and nanosecond pulsed laser ablation

The influence of the incorporation of boron in diamond-like carbon (DLC) films on the microstructure of the coatings has been investigated. The boron-containing DLC films (a-C:B) have been deposited by pulsed laser deposition (PLD) at room temperature in high vacuum conditions, by ablating graphite and boron targets either with a femtosecond pulsed laser (800 nm, 150 fs, fs-DLC) or with a nanosecond pulsed laser (248 nm, 20 ns, ns-DLC). Alternative ablation of the graphite and boron targets has been carried out to deposit the a-C:B films. The film structure and composition have been highlighted by coupling Field Emission Scanning Electron Microscopy, Electron Energy Loss Spectroscopy and High Resolution Transmission Electron Microscopy. Using the B K-edge, EELS characterization reveals the boron effect on the carbon bonding. Moreover, the plasmon energy reveals a tendency of graphitization associated to the boron doping. Pure boron particles have been characterized by HRTEM and reveal that those particles are amorphous or crystallized. The nanostructures of the boron-doped ns-DLC and the boron-doped fs-DLC are thus compared. In particular, the incorporation of boron in the DLC matrix is highlighted, depending on the laser used for deposition. Electrical measurements show that some of these films have potentialities to be used in low temperature thermometry, considering their conductivity and temperature coefficient of resistance (TCR) estimated within the temperature range 160-300 K.     

Morphology control and luminescence properties of YAG:Eu phosphors prepared by spray pyrolysis

Starting from nitrate aqueous solutions with citric acid and polyethylene glycol (PEG) as additives, Y₃Al₅O₁₂:Eu (YAG:Eu) phosphors were prepared by a two-step spray pyrolysis (SP) method. The obtained YAG:Eu phosphor particles have spherical shape, submicron size and smooth surface. The effects of process conditions of the spray pyrolysis on the crystallinity, morphology and luminescence properties of phosphor particles were investigated. The emission intensity of the phosphors increased with increasing of sintering temperature and solution concentration due to the increase of the crystallinity and particles size, respectively. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.10 g/ml in the precursor solution. Compared with the YAG:Eu phosphor prepared by citrate-gel (CG) method with non-spherical morphology, spherical YAG:Eu phosphor particles showed a higher emission intensity.     

The UV and VUV luminescence properties of the phosphor Mg2GeO4:Tb

A novel green phosphor Mg₂GeO₄:Tb³⁺ with pure phase was prepared by the solid state reaction. The luminescence properties were investigated in detail. The diffusion reflection spectra of the undoped and Tb³⁺ doped Mg₂GeO₄ phosphors were recorded, the result reveals that there is an absorption band superposition of the host material and Tb³⁺ ion. The study on the excitation and diffusion spectra shows that there is an effective energy transfer from the host material to Tb³⁺ ion. Under 277 and 172 nm excitation, the phosphor presents predominant green emission at 543 and 547 nm respectively. The excitation intensity at 172 nm is about 1.8 times of that at 272 nm. The promising luminescence properties make it a candidate for application in Plasma Display Panel.     

Effect of deposition temperature on morphology and magnetic properties of Co50Fe50 thin films produced by femtosecond pulsed laser deposition

Deposition temperature effect on morphological, topological and magnetic characteristics of nanoparticle-assembled Co₅₀Fe₅₀ films produced by femtosecond pulsed laser deposition (fs-PLD) on Kapton substrate was investigated. For substrate temperature T_s ≥ 550 K, a decrement of the nanoparticle's aggregates and an increment of the nanoparticle's density were observed with respect to room temperature deposition; this in association with a strong increase of the magnetoelastic anisotropy energy lead to a reduction of the remanence ratio, a significant rise of the saturation and coercive fields and an enhancement of the saturation magnetization. The results are discussed focusing on: i) the correlation between films structure and their magnetic behavior; ii) the role of the different anisotropy energies in determining the harder in-plane magnetic behavior for T_s ≥ 550 K. The thermal strain of Kapton substrate holds an important role in generating morphological and topological characteristics of the fs-PLD films and corresponding magnetic properties.     

Structural and optical properties of Ti oxide cluster-assembled films prepared by plasma-gas-condensation

Ti and Ti oxide cluster-assembled films have been prepared using a plasma-gas-condensation apparatus. Transmission electron microscopy and electron diffraction measurement indicates that their structures vary from a face-centered-cubic (fcc) Ti phase, via an NaCl-type TiO_x phase, to an amorphous and rutile-type TiO₂ mixture phase with increasing the O₂ flow rate in the Ar/He gas mixture. Cluster shapes are spherical for the fcc phase, cubic for the NaCl-type, and spherical for the amorphous and rutile-type mixture, while the cluster size monotonically decreases with increasing O₂ flow rate. The Ti and Ti oxide cluster-assembled films have a sooty appearance, showing a very porous morphology in the scanning electron microscopy images. The electrical resistivity dramatically increases between R_O2 = 0.065 and 0.075 sccm, while the optical transmittance spectra in the visible wavelength range rapidly increases between R_O2 = 0.1 and 0.12 sccm, well reflecting the structure variations in these Ti and Ti oxide cluster-assembled films.     

Synthesis and luminescence properties of Ca8NaGd(PO4)6F2: Eu2+, Mn2+ for white LEDs

A series of luminescent emission-tunable phosphors Ca₈NaGd(PO₄)₆F₂: Eu²⁺, Mn²⁺ have been prepared by a combustion-assisted synthesis method. The X-ray diffraction measurement results indicate that the crystal structure of the phosphor is a single phase of Ca₈NaGd(PO₄)₆F₂. The photoluminescence (PL) properties of Eu²⁺ and Mn²⁺-codoped Ca₈NaGd(PO₄)₆F₂ phosphors were also investigated. The phosphors can be efficiently excited by ultraviolet (UV) light and show a blue emission band at about 450 nm and a yellow emission band at about 574 nm, which originated from the Eu²⁺ ions and the Mn²⁺ ions, respectively. The efficient energy transfer from the Eu²⁺ ions to the Mn²⁺ ions was observed and its mechanism should be a resonant type via a nonradiative dipole–quadrupole interaction. A color-tunable emission in Ca₈NaGd(PO₄)₆F₂ phosphors can be realized by Eu²⁺ → Mn²⁺ energy transfer. Our results indicate that the developed phosphor may be used as a potential white emitting phosphor for UV based white LEDs.     

Effect of activator distribution on photo- and X-ray excited luminescence properties of ZnS:Cu,Cl phosphors

ZnS:Cu,Cl phosphors were prepared by conventional solid state reaction with the aid of NaCl-MgCl₂ flux. The copper activator was introduced into the phosphor precursors by three different methods: co-precipitated with ZnS (CP), wet-coated onto ZnS powders (WC), and simply mixed with ZnS in a mortar (SM). The samples were characterized by X-ray powder diffraction, photoluminescence spectra and X-ray excited luminescence spectra. The results show that both photo- and X-ray excited luminescence intensities of the as-prepared ZnS:Cu,Cl phosphors are in the decreasing order of CP > WC > SM. The different copper activator distribution in the phosphors resulting from the different methods was the main reason responsible for the different luminescence intensity, and uniform distribution is beneficial to the luminescence of the phosphors.     

Enhanced luminescence properties of YBO3:Eu phosphors by Li-doping

Different concentrations of Li-doped YBO₃:Eu³⁺ phosphors have been prepared by the conventional solid state reaction method and were characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission measurements. An intense reddish orange emission is observed under UV excitation and the emitted radiation was dominated by an orange peak at 594 nm resulted from the ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions. The brightness of the YBO₃:Eu³⁺ phosphor was found greatly improved with Li-doping accompanied by slight improvement in the purity of the color which might be attributed to improvement in crystallinity, grain sizes and creation of oxygen vacancies with Li-doping. The observed results have been discussed in comparison with similar reported works.