飞秒激光诱导钛表面形成高空间频率周期条纹结构

利用波长为800 nm的飞秒激光,在空气和去离子水中诱导钛表面形成不同的周期条纹结构。在空气中,激光能量密度为0.265 J/cm2时,钛表面主要形成周期为500~560 nm低空间频率条纹结构;激光能量密度为0.102 J/cm2时,主要形成的是周期为220~340 nm高空间频率条纹结构。两种条纹均垂直于入射激光偏振方向,且条纹周期随着脉冲重叠数的增大而增大。在水中,除形成垂直激光偏振方向、周期为215~250 nm的高空间频率条纹结构,还形成了平行于激光偏振方向且周期约为入射激光波长八分之一的高空间频率条纹结构。利用表面等离子体理论、二次谐波及Sipe理论对各种周期条纹结构的形成机理进行分析,发现周期条纹结构的形成与钛表面氧化层有密切的关系。     

飞秒钛宝石放大激光脉冲的载波包络相位测量与控制

通过对重复频率为1 kHz的放大飞秒激光脉冲的光谱干涉实验,结合傅里叶变换进行了载波包络相位漂移的实验研究.在此基础上利用锁相环反馈控制技术实现了对载波包络相位的精密锁定,锁定后的激光脉冲稳态相位均方根误差小于80mrad,锁定时间超过3h.同时在理论上分析了光谱干涉测量放大激光脉冲载波包络相位的原理,给出了光谱干涉信号与载波包络相位的关系. 关键词： 飞秒钛宝石放大器 载波包络相位 光谱干涉 超连续     

The effects of heat treatment on microfluidic devices fabricated in silica glass by femtosecond lasers

We fabricated complex microfluidic devices in silica glass by water-assisted femtosecond laser ablation and subsequent heat treatment.The experimental results show that after heat treatment,the diameter of the microchannels is significantly reduced and the internal surface roughness is improved.The diameters of the fabricated microchannels can be modulated by changing the annealing temperature and the annealing time.During annealing,the temperature affects the diameter and shape of the protrusions in microfluidic devices very strongly,and these changes are mainly caused by uniform expansion and the action of surface tension.     

飞秒激光烧蚀石英玻璃的实验与理论研究

实验研究了800nm飞秒激光作用下石英玻璃的破坏机理和烧蚀规律，给出了破坏阈值与脉冲宽度的关系.发展了雪崩击穿模型，计算了材料的烧蚀阈值与脉冲宽度的依赖关系，烧蚀深度、烧蚀体积与脉冲能量的依赖关系，研究了导带电子的扩散对材料中激光能量的沉积、分布，以及材料的破坏阈值和烧蚀规律的影响. 关键词： 飞秒激光脉冲 破坏机理 石英玻璃 电子扩散     

Optical characterization of a GaAs/AlGaAs vertical cavity surface emitting quantum well laser structure grown by MOCVD

In this work we report on the characterization and modelling of the reflectivity of a vertical cavity surface emitting quantum well laser (VCSEQWL) grown by MOCVD. The theoretical simulation of the reflectivity was developed for the purpose of designing VCSEQWL cavity multilayer reflectors. Included in the model are the effects of the n = 1 electron/heavy hole (e-hh) and electron/light hole (e-lh) exciton absorptions and the dispersion of the multilayer materials on the cavity mirror reflectivity. Using this model we analysed the influence of systematic deviations of the multilayer thicknesses on the VCSEQWL cavity reflectivity. Good agreement was achieved between the measured and simulated reflectivity if we allowed for systematic deviations in the thicknesses of the epilayers of ± 2.5%. Electroluminescence measurements from the VCSEQWL showed the n = 1 (e-hh) quantum well transition to be matched to the laser cavity resonance. Both calculated and measured results showed that when the n = 1 (e-hh) exciton transition matched the microcavity resonance the exciton absorption was strongly enhanced due to the multiple reflections of the incident light beam in the cavity.     

Preparation of biomedical Ag incorporated hydroxyapatite/titania coatings on Ti6AI4V alloy by plasma electrolytic oxidation

Nano-Ag incorporated hydroxyapatite/titania （HA/TiO2） coatings were deposited on Ti6A14V substrates by the plasma electrolytic oxidation process. Compared with the substrate, the deposited coatings display attractive mechani- cal and biomedical properties. First, the coatings have stronger wear resistance and corrosion resistance. Second, they show a strong antibacterial ability. The mean vitality of the P. gingivalis on the coating surfaces is reduced to about 21%. Third, the coatings have good biocompatibility. The mean viability of the fibroblast cells on the coating surface is increased to about 130%. With these attractive properties, Ag incorporated HA/TiO2 coatings may be useful in the biomedical field.     

Preparation of biomedical Ag incorporated hydroxyapatite/titania coatings on Ti6Al4V alloy by plasma electrolytic oxidation

Nano-Ag incorporated hydroxyapatite/titania(HA/TiO2) coatings were deposited on Ti6Al4V substrates by the plasma electrolytic oxidation process. Compared with the substrate, the deposited coatings display attractive mechanical and biomedical properties. First, the coatings have stronger wear resistance and corrosion resistance. Second, they show a strong antibacterial ability. The mean vitality of the P. gingivalis on the coating surfaces is reduced to about 21%.Third, the coatings have good biocompatibility. The mean viability of the fibroblast cells on the coating surface is increased to about 130%. With these attractive properties, Ag incorporated HA/TiO2 coatings may be useful in the biomedical field.     

温度对飞秒激光脉冲在NaCl溶液中成丝产生的超连续谱的影响

利用飞秒激光脉冲在NaCl溶液中成丝,研究了溶液温度对飞秒激光成丝过程中产生的超连续谱的影响.发现在激光脉冲能量较低时,溶液温度对超连续谱的影响几乎可以忽略;而在激光脉冲能量较高时,随着NaCl溶液温度的升高,超连续谱呈现出被压缩的趋势.此外,在激光脉冲能量较高的情况下, NaCl中会产生大量的气泡.通过分析,得出了飞秒激光在溶液中成丝产生的气泡是影响超连续谱发射的主要因素.     

频域标定飞秒脉冲干涉自相关迹及钛宝石振荡器实时啁啾监测

采用频域处理的方法首次在频域标定飞秒激光脉冲干涉自相关迹的时间扫描.计算被测脉冲的均方根宽度和啁啾参数，并以此为依据在实验中优化钛宝石振荡器的调节从而获得接近变换极限的115fs脉冲.该方法只涉及到数值积分和快速傅里叶变换，在实验中完全可以用于实时监测振荡器的运行情况. 关键词： 频域标定 钛宝石振荡器 飞秒脉冲 干涉自相关迹     

空气中飞秒激光等离子体荧光辐射光谱研究

系统地研究了不同聚焦条件下飞秒激光空气等离子体的荧光辐射特性以及空间演化情况.在紧聚焦情况下,由于焦点附近比较高的激光强度以及比较高的电子密度,辐射光谱表现为连续谱和线状原子光谱的叠加.在弱聚焦情况下,辐射光谱主要由很多分子线谱组成,而没有观测到连续谱的产生.还研究了光谱谱线强度随激光传输距离的演化情况,结果显示,光谱谱线的强度变化在一定程度上间接反映了等离子体细丝的演化情况.     

The photosensitive effect of Ce on the precipitation of Ag nanoparticles induced by femtosecond laser in silicate glass

This paper studies the photosensitive effect of cerium oxide on the precipitation of Ag nanoparticles after femtosecond laser irradiating into silicate glass and successive annealing. Spectroscopy analysis and diffraction efficiency measurements show that the introduction of cerium oxide may increase the concentration of Ag atoms in the femtosecond laser-irradiated regions resulting from the photoreduction reaction Ce³⁺ + Ag⁺ \to Ce³⁺ + Ag⁰ via multiphoton excitation. These results promote the aggregation of Ag nanoparticles during the annealing process. It is also found that different concentrations of cerium oxide may influence the Ag nanoparticle precipitation in the corresponding glass.     

The dependence on optical energy of terahertz emission from air plasma induced by two-color femtosecond laser-pulses

The generation of terahertz （THz） emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses com- posed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy.     

飞秒激光空气等离子体发射光谱的实验研究

对强飞秒激光聚焦在空气中所激发的等离子体的发射光谱进行了实验研究.结果表明,光谱特征表现为短波段(截至波长为340 nm)强烈的连续谱和长波段(波长在800 nm附近)强度相对较低的线光谱.在脉冲宽度(50 fs)保持不变而不断调节激光脉冲能量时,等离子体光谱形状的特征基本相似;当激光脉冲能量(1 mJ)保持不变而脉冲宽度从50 fs增加至500 fs和1 ps时,连续谱的峰值(500 nm)显得格外突出,并开始呈现出线光谱特征. 关键词： 飞秒激光 激光空气等离子体 发射光谱 线光谱     

Phase transformation and nanograting structure on TiO2 rutile single crystal induced by infrared femtosecond laser

In this paper, TitaiJum dioxide （TiO2） rutile single crystal was irradiated by infrared femtosecond laser pulses with repetition rate of 250 kHz. For a P-polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was formed . The periodicity is much less than the laser wavelength. The direction of nanograting alignment depends on the polarization laser beam. Micro-Raman spectra show that the intensity of Eg Raman vibrating mode of rutile phase increases and that of Alg Raman vibrating mode decreases apparently within the ablation crater. With the increase of irradiation time and laser average power, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO2 single crystal is partly transformed into anatase phase.[第一段]     

飞秒激光等离子体通道传导能量特性的研究进展

基于强飞秒激光诱导等离子体通道的基本性质,分析了等离子体通道在传导电能和射频电磁能时的一些基本问题。综述了飞秒激光等离子体通道传输电能和电磁能方面的新概念和新技术,重点描述了该领域近几年所取得的一些理论及应用的最新成果。最后,展望了飞秒激光等离子体通道在传导能量技术领域中的发展趋势。     

三光束飞秒激光干涉在GaP,ZnSe表面诱导二维复合纳米-微米周期结构

报道了三光束飞秒激光干涉在GaP和ZnSe晶体表面诱导二维复合纳米-微米周期结构.改变三束光的偏振组合方式,可以得到不同的纳米-微米复合结构.理论计算了相应偏振条件下光场强度分布、椭偏度分布和偏振方向分布.实验和理论计算结果表明,烧蚀斑上的微米长周期结构是由三光束干涉的强度花样决定,短周期纳米结构是由光场的偏振干涉花样决定.这些研究在纳米材料制备、超高密度光存储以及材料特性周期性调制等方面有很大的应用前景.     

基于飞秒激光等离子体丝诱导击穿光谱探测土壤重金属Cr元素含量

本文基于飞秒激光等离子体丝诱导击穿光谱对土壤重金属Cr元素含量进行了实验研究.利用荧光法对等离子体丝的长度进行测量,给出了在不同焦距聚焦透镜作用下土壤中Cr425.5 nm的谱线强度空间分布,实验给出了Cr元素的定标曲线.实验结果表明,土壤中Cr元素浓度分析测量的相对标准偏差小于5%,土壤中重金属Cr元素的检测极限为7.85 ppm.表明飞秒激光等离子体丝诱导击穿光谱技术在土壤重金属Cr元素含量的定量探测方面是完全可行的.     

时间整形飞秒激光诱导熔融硅表面纳米周期条纹的电子动力学研究

研究了时间整形飞秒激光在熔融硅表面诱导纳米周期条纹结构的电子动力学过程.通过引入非线性电离机制和表面等离子激元的瞬态作用机理,建立了关于时间整形飞秒激光诱导和调控熔融硅表面纳米周期条纹结构的电子动力学模型,并应用该模型研究获得了纳米条纹周期与时间整形脉冲时间间隔的定量关系.理论研究结果表明,通过调节时间整形脉冲的时间间隔可以实现操控表面等离子激元与激光瞬态干涉过程中的波矢配对,最终可实现对诱导的纳米条纹周期的调控.此模型预测得到的纳米条纹周期与实验结果符合得很好.该研究对于深刻理解整形脉冲链诱导材料表面纳米周期结构的电子动力学操纵机制以及对条纹周期的调控都具有重要的理论价值.     

Measurement of CO,HCN, and NO productions in atmospheric reaction induced by femtosecond laser filament

It is proved that the chemical reaction induced by femtosecond laser filament in the atmosphere produces CO, HCN, and NO, and the production CO and HCN are observed for the first time. The concentrations of the products are measured by mid-infrared tunable laser absorption spectroscopy. In the reduced pressure air, the decomposition of CO₂ is enhanced by vibration excitation induced by laser filament, resulting in the enhanced production of CO and HCN. At the same time, the CO and HCN generated from the atmosphere suffer rotation excitation induced by laser filament, enhancing their absorption spectra. It is found that NO, CO, and HCN accumulate to 134 ppm, 80 ppm, and 1.6 ppm in sealed air after sufficient reaction time. The atmospheric chemical reaction induced by laser filament opens the way to changing the air composition while maintaining environmental benefits.     

Variety of nanostructures induced by femtosecond laser pulses on surface of Au/Cr film stack

Several nanostructures were obtained after irradiation with femtosecond laser pulse (130 fs, 800 nm, 1 kHz pulse repetition frequency) on Au/Cr film stack. The influence of laser parameters such as fluence (0.5 J/cm², 1.5 J/cm², 3 J/cm²) and the number of pulse were investigated. With single pulse irradiation, the nanoline and nonoparticle were obtained for the pulse fluence of 0.5 J/cm² and 3 J/cm², respectively. The formation mechanism of those nanostructures was discussed. The results of this experiment demonstrate that different kinds of nanostructures could be formed by varying the laser parameters such as fluence and the number of pulse.