Mechanism study of femtosecond laser induced selective metallization (FLISM) on glass surfaces

We investigate the mechanism of selective metallization on glass surfaces with the assistance of femtosecond laser irradiation followed by electroless plating. Irradiation of femtosecond laser makes it possible to selectively deposit copper microstructures in the irradiated area on glass surfaces coated with silver nitrate films. The energy-dispersive X-ray (EDX) analyses reveal that silver atoms are produced on the surface of grooves formed by laser ablation, which serve as catalysis seeds for subsequent electroless copper plating. (C) 2008 Elsevier B.V. All rights reserved.

Femtosecond pulse laser-induced self-organized nanogratings on the surface of a ZnSe crystal

Periodic nanostructures are observed on the surface of ZnSe after irradiation by a focused beam of a femtosecond Ti:sapphire laser, which are aligned perpendicular to the laser polarization direction. The period of self-organized grating structures is about 160 nm. The phenomenon is interpreted in terms of interference between the incident light field and the surface scattered wave of 800-nm laser pulses. With the laser polarization parallel to the moving direction we produce long-range Bragg-like gratings by slowly moving the crystal under a fixed laser focus. The nanograting orientation is adjusted by laser polarization and the accumulation effect.

Laser ranging based on electro-optic switch

Based on electro-optic switch effect in crystal, a novel laser ranging method is proposed. CW-laser emitted by laser transmitter propagates forward to the measured target, after being reflected by the target, and then goes back to the transmitter. Close to the transmitter, a special mono-block LiNbO3 crystal is added into the round-trip light beams. High-voltage pulses with the sharp enough changes in rising edges are loaded on the crystal. Based on electro-optic effect, double refraction and internal double reflection effect in crystal, the crystal cuts off the round-trip light beams, and reflects a light pulse cut out by the crystal to a detector aside from the original beam path. The pulse width T is the period that laser propagates forward and back between the crystal and the target. The feasibility of the new idea is proved by our experiments and a brand-new way for the laser ranging is provided. (c) 2005 Elsevier GmbH. All rights reserved.

激光诱导等离子体开关控制脉宽实验研究

利用激光诱导等离子体开关技术，在1064nm的Nd：YAG固体激光器上获得了脉宽4．4～6．4ns的短脉冲激光输出。激光电离空气产生的等离子体开关控制脉冲宽度时，聚焦透镜焦距越短，压缩后的脉宽越窄，但激光能量损耗越大。压缩后的激光脉宽与激光能量近似成双曲线关系。在控制脉宽光路的焦点处放置带孔的Cu薄片可抑制等离子体的扩散，得到了脉宽最短可达4．4ns的激光输出。

355 nm脉冲激光诱导等离子体开关削波

利用激光诱导等离子体开关技术,对355 nm脉冲激光自削波进行了实验和理论研究。分别采用5种不同焦距的透镜,集中讨论了透镜焦距及激光器输出单脉冲能量对脉宽压缩的影响,发现采用焦距为200 mm的透镜能够获得最佳的脉冲压缩效果。在聚焦透镜焦距200 mm,单脉冲能量160 mJ时,获得最短脉宽3.47 ns；在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了脉宽最短达2.11 ns的脉冲激光输出。此外,根据实验结果得到了355 nm激光空气击穿阈值,并与理论估算值进行比较,两者结果较为一致。

Inductively coupled plasma etching of two-dimensional InP/InGaAsP-based photonic crystal

Inductively coupled plasma (ICP) etching of InP in Cl-2/BCl3 gas mixtures is studied in order to achieve low-damage and high-anisotropy etching of two-dimensional InP/InGaAsP photonic crystal. The etching mechanisms are discussed and the effect of plasma heating on wafer during etching is analyzed. It is shown that the balance between the undercut originating from plasma heating and the redeposition of sputtering on the side-wall is crucial for highly anisotropic etching, and the balance point moves toward lower bias when the ICP power is increased. High aspect-ratio etching at the DC bias of 203 V is obtained. Eventually, photonic crystal structure with nearly 90 degrees side-wall is achieved at low DC bias after optimization of the gas mixture.

Optical and structural properties of self-assembled ZnO QD chains by L-MBE

ZnO complex 3D nano-structures have been self-organized on Al2O3 (0 0 0 1) substrate by laser molecular beam epitaxy (L-MBE). It is shown by AFM morphology that the structure is composed of ID quantum dot chains (QDCs) and larger nano-islands at the nodes of QDCs. The formation mechanism of the nano-structure is also investigated. XRD results indicate that the nano-structure is highly c-axis oriented, with the aligned in-plane oriented domains. Time-integrated photoluminescence (TIPL) of the sample shows obvious blue-shift and broadening of the near band-edge (NBE) emission at room temperature, which are related to the quantum confinement effects. Time-resolved PL (TRPL) result shows bi-exponential decay behavior of ZnO QDCs, with a fast decay time of 38.21 ps and a low decay time of 138.19ps, respectively, which is considered to be originated from the interdot coupling made by coherent emission and reabsorption of the photons in QDCs. (C) 2007 Elsevier B.V. All rights reserved.

Influence of Laser Wavelength on Laser-induced Breakdown Spectroscopy Applied to Semi-Quantitative Analysis of Trace-Elements in a Plant Sample

Laser-induced breakdown spectroscopy (LIBS) as a powerful analytical technique is applied to analyze trace-elements in fresh plant samples. We investigate the LIBS spectra of fresh holly leaves and observe more than 430 lines emitted from 25 elements and molecules in the region 230-438 nm. The influence of laser wavelength on LIBS applied to semi-quantitative analysis of trace-element contents in plant samples is studied. The results show that the UV laser has lower relative standard deviations and better repeatability for semi-quantitative analysis of trace-element contents in plant samples. This work may be helpful for improving the quantitative analysis power of LIBS applied to plant samples.

Hot-corrosion behaviors of overlay-clad yttria-stabilized zirconia coatings in contact with vanadate-sulfate salts

A dense clad overlay with chemical inertness was achieved on top of the plasma-sprayed YSZ thermal barrier coatings by laser in order to protect them from hot-corrosion attack. The Al2O3-clad YSZ coating exhibited good hot-corrosion behavior in contact with salt mixture of vanadium pentoxide (V2O5) and sodium sulfate (Na2SO4) for a longtime of 100 h at 1173 K. The LaPO4-clad YSZ coating showed corrosion resistance inferior to the Al2O3-clad one. Yttria was leached from YSZ by reaction between Y2O3 and V2O5, which caused progressive destabilization transformation of YSZ from tetragonal (t) to monoclinic (m) phase. The chemical inertness of the clad layers and the restrained infiltration of the molten corrosive salts by the dense clad layers were primary contributions to improvement of the hot-corrosion resistances.

Microstructure and wear properties of laser clad Fe based amorphous composite coatings

A FeNiSiBV amorphous composite coating was developed by laser cladding of metallic powders on AISI 1020 low carbon steel substrate. The coatings were studied using X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The coating reveals different microstructures along the depth of the coating. The transition zone exhibits good metallurgical bonding between the substrate and the coating. The layer consists of amorphous phase in majority and nanocrystalline phase/crystalline phase in minority. Accompanied with the nanocrystalline phase, the amorphous phase is concentrated in the middle of the coating. The crystalline phase in the coating is identified as Fe2B. A gradient distribution of the microhardness ranges from 1208 HV0.2 to 891 HV0.2 in the coating along the depth. The coating shows higher microhardness and better wear property than the substrate.

激光诱导等离子体光谱法检测合金钢组分的实验研究

激光诱导击穿光谱技术(LIBS)具有无需样品制备,原位快速分析,可进行实时控制的特点使其在钢铁冶炼控制中具有巨大的实际应用价值。本文以波长为1 064 nm的Nd∶YAG调Q固体激光器为激发光源,CCD为探测器,高合金钢GBW01605—01609系列为样品,在建立的LIBS实验装置上研究激光与合金钢之间的相互作用。系统地研究了观测距离、激光能量对高合金钢样品中激光诱导击穿谱特性的影响,并分析了LIBS信号的时间分辨特性,确定了将LIBS用于合金钢微量元素定量分析时的最佳实验条件。

利用激光诱导击穿光谱对铝合金成分进行多元素同时定量分析

利用激光诱导击穿光谱定量分析了铝合金中多种元素的成分。采用Nd∶YAG脉冲激光器,在空气环境下烧蚀铝合金固体样品获得等离子体。利用多通道光栅光谱仪和CCD检测器对200～980nm波长范围的光谱进行同时检测。研究了检测时延、激光脉冲能量、元素深度分布对光谱强度的影响,考虑这些因素之后对实验参数进行了优化。在优化的实验参数下对国家标准铝合金样品中的八种元素Si,Fe,Cu,Mn,Mg,Zn,Sn及Ni进行了定标,并利用定标曲线对一种铝合金样品进行了定量分析。实验结果表明,测量结果的相对标准偏差(RSD)最大为5.89%,相对误差在-20.99%～15%范围内,说明对铝合金样品成分进行定量分析,激光诱导击穿光谱是一种有效的光谱分析工具,但是分析结果的准确度仍需要提高。

激光诱导放电毛化技术中放电坑的表面形貌研究

利用高重频YAG激光作用在固体表面所产生的等离子体使工件和电极之间在电压远低于击穿阈值的条件下产生放电.实验结果显示,放电坑基本上呈火山坑形,既有单坑结构,也有多坑结构,其形貌受到放电波形、电源极性、放电介质等因素的影响.放电坑表面形貌的规律是:①除了涂油时的阳极放电坑是单坑结构以外,其他条件下的放电坑都是复合多坑结构;②单坑结构呈火山坑形,坑底为圆弧形,熔凝物堆积在坑的边缘,多坑结构则是一个大的放电坑中有多个凸起尖峰.

球墨铸铁变换激光束淬火性能的研究

采用经过二元光学元件变换呈二维点阵7*7分布的脉冲激光束对球墨铸铁材料进行表面淬火处理，研究激光参数变化对铸铁表面的粗糙度、硬化层深度、显做硬度和耐磨性等的影响。结果表明，在一定的能量范围内，随着能量的增加，粗糙度略呈增长的趋势，硬化层深也略有增加，并存在一个硬化层深极限值。硬度峰值差别很小，而相变硬化区差别则很大。耐磨性试验表明，随着能量的增加，耐磨性有提高的趋势。

钢基身管内镀铬层下的激光淬火基体界面腐蚀与铬层剥落

钢基身管镀铬层在高温腐蚀性气体中服役,采用YAG激光器对身管内表面作螺旋线状离散淬火预处理后再电镀铬的复合工艺,形成了基体界面呈激光淬火区/激光未处理区周期性变化的铬层/基体结构.对该身管进行高温腐蚀介质为火药气体的靶场实验.对实验后的基体界面腐蚀形貌与铬层剥落的关系研究表明:次界面裂纹的形成是基体界面高温气体腐蚀的根本原因,基体界面腐蚀的结果是形成基体烧蚀坑,烧蚀坑上的铬层以断裂形式剥落.激光淬火预处理钢基体通过抑制次界面裂纹的形成避免了基体界面高温气体腐蚀损伤,提高了铬层的抗剥落能力.