Control of electrical resistance of TiO2 films by short-pulse laser irradiation

Titanium dioxide (TiO₂) films were irradiated with a femtosecond laser beam to alter their electrical resistances. The TiO₂ film was produced by aerosol beam deposition. The wavelength, pulse duration, and repetition rate of the femtosecond laser scanned across the sample surface were 800 nm, 100 fs, and 1 kHz, respectively. By attenuating the laser fluence on the TiO₂ film, a range was found in which the electrical resistance of the TiO₂ film was varied even though the morphology of the film surface was not changed.     

Formation of graphene on amorphous SiC film by surface-confined heating with electron beam irradiation

It is demonstrated experimentally that graphene can form on the surface of an amorphous SiC film by irradiating electron beam (e-beam) at low acceleration voltage. As the electron irradiation fluency increases, the crystallinity and uniformity of graphene improve, which is confirmed by the changes of the measured Raman spectra and secondary electron microscopy images. Due to the shallow penetration depth of e-beam with low acceleration voltage, only the region near the surface of SiC film will be heated by the thermalization of irradiated electrons with multiple scattering processes. The thermalized electrons are expected to weaken the bond strength between Si and C atoms so that the thermal agitation required for triggering the sublimation of Si atoms decreases. With these assistances of irradiated electrons, it is considered that graphene can grow on the surface of SiC film at temperature reduced substantially in comparison with the conventional vacuum annealing process.     

脉冲激光辐照TiO2/SiO2薄膜热效应研究

 采用1.06 μm单脉冲激光在不同能量密度下辐照特殊光电系统中典型薄膜光学元件，理论分析了激光辐照薄膜元件产生的温度场和热应力场，在此基础上建立了激光辐照多层薄膜的物理模型，计算软件使用ANSYS软件的热分析模块对激光辐照薄膜元件产生的温度场和热应力场进行了模拟，分别给出不同激光能量密度下薄膜表面光斑中心的温度场、径向温度场和轴向温度场分布；同时给出不同能量密度下薄膜的轴向、径向和环向热应力分布。并对激光辐照薄膜元件产生的温度场、热应力场进行了分析，阐明了原因。     

脉冲激光辐照TiO2/SiO2薄膜热效应研究

采用1.06 μm单脉冲激光在不同能量密度下辐照特殊光电系统中典型薄膜光学元件,理论分析了激光辐照薄膜元件产生的温度场和热应力场,在此基础上建立了激光辐照多层薄膜的物理模型,计算软件使用ANSYS软件的热分析模块对激光辐照薄膜元件产生的温度场和热应力场进行了模拟,分别给出不同激光能量密度下薄膜表面光斑中心的温度场、径向温度场和轴向温度场分布;同时给出不同能量密度下薄膜的轴向、径向和环向热应力分布。并对激光辐照薄膜元件产生的温度场、热应力场进行了分析,阐明了原因。     

Synthesis and characterization of composite Au/TiO2 nanoparticles by laser irradiation

Composite Au/TiO₂ nanoparticles were synthesized by laser ablation of gold plate in TiO₂ sol. The nanoparticles were characterized by UV-visible spectroscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The peak of surface plasmon is at 550 nm with a red shift of 30 nm compared with that of Au nanoparticles in water. Monolayers of composite Au/TiO₂ nanoparticles were obtained by dip-coating technique. The XRD pattern of Au/TiO₂ powders resembles a mixture of anatase TiO₂ and gold.     

Formation of extended periodic microstructures by “Point” irradiation of gold film by femtosecond laser pulses

Extended periodic microstructures are formed on a thin gold film by femtosecond laser radiation. The structure length is an order of magnitude larger than the typical size of the irradiated region. The detection of gold photoions generated in the process of the microstructuring ensures a high-sensitivity on-line diagnostics of this phenomenon.     

一步法紫外曝光制备TiO2光敏凝胶光栅的初步研究

 以钛酸丁酯和苯甲酰丙酮为原料，经sol-gel工艺，获得具有负性光刻胶性质的TiO₂光敏凝胶薄膜。它的敏感波长在360nm附近，与反应生成的螯合环有关。结合掩模曝光和显影工艺，将条状或网格状的光栅图形引入光敏凝胶表面，获得光敏凝胶光栅。     

Soliton mode-locked fiber laser with high-quality MBE-grown Bi_2Se_3 film

In this work, a soliton mode-locked erbium-doped fiber laser(EDFL) with a high-quality molecular beam epitaxy(MBE)-grown topological insulator(TI) Bi_2Se_3 saturable absorber(SA) is reported. To fabricate the SA device, a 16-layer Bi_2Se_3 film was grown successfully on a 100 μm thick SiO_2 substrate and sandwiched directly between two fiber ferrules. The TI-SA had a saturable absorption of 1.12% and a saturable influence of 160 MW/cm~2.After inserting the TI-SA into the unidirectional ring-cavity EDFL, self-starting mode-locked soliton pulse trains were obtained at a fundamental repetition rate of 19.352 MHz. The output central wavelength, pulse energy,pulse duration, and signal to noise ratio of the radio frequency spectrum were 1530 nm,18.5 p J, 1.08 ps, and 60d Bm, respectively. These results demonstrate that the MBE technique could provide a controllable and repeatable method for the fabrication of identical high-quality TI-SAs, which is critically important for ultra-fast pulse generation.     

一步法紫外曝光制备TiO2光敏凝胶光栅的初步研究

以钛酸丁酯和苯甲酰丙酮为原料,经sol-gel工艺,获得具有负性光刻胶性质的TiO2光敏凝胶薄膜。它的敏感波长在360nm附近,与反应生成的螯合环有关。结合掩模曝光和显影工艺,将条状或网格状的光栅图形引入光敏凝胶表面,获得光敏凝胶光栅。     

光纤激光器阵列的多抖动法相干合成

采用自行设计的基于大规模可编程门阵列（FPGA）结构的控制电路,实现了4路光纤激光的多抖动法相干合成。对大气湍流和机械振动引起的相位噪声进行了有效补偿,使远场光斑条纹对比度由开环时的0.21提高到了闭环时的0.93,闭环时远场特定孔径内的能量较开环时提高了3.3倍。该方法还对人为抖动光纤引起的较高频率噪声具有很好的抑制作用,系统闭环后,远场光斑条纹对比度可达到0.72。     

Possible excitation of a fast sodium beam by laser irradiation

We present results of model calculations concerning the fraction of excited atoms obtained by laser irradiation of a fast sodium atom beam (100–400 eV kinetic energy). We calculated relative absorption probabilities as a function of the intersection angle between the two beams, the atom-beam energy, the atom-beam energy spread and the atom-beam divergence. The fraction of excited atoms that can be obtained at 300 eV is at least a factor of 5 smaller than in the case of a thermal beam, due to the divergence and energy spread of the fast atom beam giving rise to a large Doppler broadening.     

Fiber laser annealing of nanocrystalline PZT thick film prepared by aerosol deposition

Nanocrystalline PZT thick films (1 mm square and over 10 μm thick) directly deposited onto stainless-steel substrates (PZT/SUS) by aerosol deposition (AD) technique and then annealed using focused laser beam with a fiber laser to suppress thermal damage to the back sides of the PZT/SUS and substrate near the film edge and to retain the dielectric and/or ferroelectric properties of the PZT/SUS. Compared with CO₂ laser annealing, fiber laser annealing suppressed thermal damage to the substrate. Compared with PZT/SUS annealed at 600 °C using an electric furnace, PZT/SUS annealed at 600 °C using a fiber laser showed superior properties, namely, dielectric constant ? > 1200 at a frequency of 100 Hz, remanent polarization P_r > 30 μC/cm², and coercive field strength E_c < 50 kV/cm at a frequency of 10 Hz. Furthermore, the grain growth for the PZT/SUS formed by AD technique and annealed by fiber laser irradiation was occurred within the laser spot size.     

Generation of a hollow laser beam by a multimode fiber

A simple method to generate a hollow laser beam by multimode fiber is reported. A dark hollow laser beam is generated from a multimode fiber and the dependence of the output beam profile on the incident angle of laser beam is analyzed. The results show that this hollow laser beam can be used to trap and guide cold atoms.     

离子束增强沉积VO_2多晶薄膜的温度系数

用改进的离子束增强沉积方法和恰当的退火从V2 O5粉末直接制备了VO2 多晶薄膜 .实验测试表明 ,薄膜的取向单一、相变特性显著、结构致密、界面结合牢固、工艺性能良好 ,薄膜的电阻温度系数 (TCR)最高可达 4 2 3% K .从成膜机理出发 ,较详细地讨论了离子束增强沉积VO2 多晶薄膜的TCR高于VOx 薄膜的TCR的原因 .分析认为 ,单一取向的VO2 结构使薄膜晶粒具有较高的电导激活能 ,致密的薄膜结构减少了氧空位和晶界宽度 ,使离子束增强沉积VO2 多晶薄膜结构比其他方法制备的VOx 薄膜更接近于单晶VO2 是其具有高TCR的原因     

Fe-doped ZnS film fabricated by electron beam evaporation and its application as saturable absorber for Er:ZBLAN fiber laser

High-quality Fe-doped Zn S films have been fabricated by electron beam evaporation. After the doping, the fabricated films still maintain the preferential crystalline orientation and phase purity of the host Zn S. According to the observation of surface morphology, the root mean-square roughness of the samples increases slightly with the increase of doping content.All of the prepared samples are in cubic zinc blende structure of Zn S. Transmission spectrum confirms a more obvious dip near 3 μm with higher dopant concentration and it can be attributed to the typical ~5E→~5T_2 transition of Fe~(2+). Fe-doped Zn S film is also successfully used for Q-switched Er:ZBLAN fiber laser.     

Photoconductive properties of titanium dioxide film modified by femtosecond laser irradiation

Titanium dioxide (TiO₂) films were irradiated with a femtosecond laser to alter their photoconductive properties. The laser wavelength and pulse duration were 775 nm and 150 fs, respectively. The TiO₂ films irradiated with the femtosecond laser were darkened without changing the topography of the TiO₂ film surface. The electrical resistances of the films as a function of time were measured under visible-light illumination. The transient electrical resistances decreased as time was increased after turning on the light. There were two stages in the reduction process of the electrical resistance.     

强激光辐照下纳米晶体铜薄膜层裂破坏的实验研究

采用强激光辐照加载技术和激光速度干涉(VISAR)测试技术，对纳米晶体铜薄膜的层裂特性进行实验测量和分析.基于VISAR实测的自由面速度波形，计算得到纳米晶体铜薄膜在超高拉伸应变率下的层裂强度高达3 GPa，明显高于多晶铜的层裂强度, 其原因归咎于纳米晶体材料中存在大量晶界阻碍了位错运动.     

强激光辐照下纳米晶体铜薄膜层裂破坏的实验研究

采用强激光辐照加载技术和激光速度干涉(VISAR)测试技术,对纳米晶体铜薄膜的层裂特性进行实验测量和分析.基于VISAR实测的自由面速度波形,计算得到纳米晶体铜薄膜在超高拉伸应变率下的层裂强度高达3 GPa,明显高于多晶铜的层裂强度, 其原因归咎于纳米晶体材料中存在大量晶界阻碍了位错运动. 关键词： 纳米晶体铜薄膜 层裂 激光辐照