应用激光蚀刻不同微织构表面的润湿性

运用激光微织构技术, 通过控制微凹坑形状、间距、深度等参数, 在45#钢表面制备了一组表面算术平均偏差S_a相同但表面微观结构不同的试件. 使用Talysulf CCI Lite 非接触式三维光学轮廓仪对表面进行测量, 采用ISO 25178三维形貌表征参数对其形貌进行表征. 在SL200 KS光学法固液接触角和界面张力仪上针对32#汽轮机油进行润湿性试验, 分析了温度、液滴体积、表面结构特征等因素对润湿性的影响, 并借助ISO25178中部分参数对固体表面形貌随机特征与其润湿性之间的关联性进行了量化研究. 基于固液本征接触角为锐角, 研究结果表明: 固液接触角在润湿过程中先迅速减小, 之后逐渐趋于稳定; 固液平衡接触角随温度的升高而减小, 随液滴体积的增大先增大后减小; 激光微织构能够改变表面润湿性, S_a相同的表面, 微织构形状、方向均影响表面润湿性, 当槽状微织构表面的槽方向与液滴铺展方向一致时, 润湿效果最优. ISO25178系列三维形貌表征参数中幅度参数(S_ku, S_sk)、空间参数(S_tr, S_al)、混合参数(S_dq, S_dr)与表面润湿性之间具有较强的关联性: S_ku, S_al, S_dr越大, S_sk, S_tr, S_dq 越小的表面, 固液平衡接触角越小, 表面润湿性越好.     

多晶硅表面周期性微结构的激光制备与性能研究

为了减小多晶硅表面入射光的反射率,提高太阳能电池的光电效率,利用紫外纳秒激光器在多晶硅表面制备不同深度、不同间距的微凹坑点阵绒面,研究织构形貌对反射率及光电转换效率的影响。通过激光频率的改变实现微凹坑深度的变化,通过微凹坑排布方式的改变实现微凹坑间距的变化;使用光纤光谱仪测量多晶硅表面反射率并通过激光共聚焦显微镜观察微凹坑形貌;在PC1D软件中建立多晶硅入射光反射模型并模拟不同点阵间距下的多晶硅短路电流和开路电压,计算光电转换效率和填充因子。研究表明,不同频率(300 kHz、200 kHz、150 kHz、50 kHz)和点阵排布方式(300×300、310×310、350×350、400×400)对多晶硅表面的反射率和光电转换效率影响显著,随着频率增大,多晶硅试样反射率先减小后增加最后保持稳定;随着点阵排布密集程度增加,多晶硅试样光电转换效率逐渐提高。实验结果显示当激光频率为150 kHz,点阵分布为400×400时,多晶硅表面微凹坑成型较好,表面平均反射率为3.32%,多晶硅电池的效率为18.80%,相较于未制绒多晶硅电池提高25.9%。     

激光微织构拉刀制备与能量残留

基于将表面织构技术应用于刀具表面可以有效改善刀具切削性能，结合拉刀材料性能，提出一种微织构拉刀的加工方法。利用激光加工技术在拉刀后刀面加工出一种微织构，并研究各种加工参数对织构形貌的影响。深入研究Q频、功率、扫描速度及加工次数对织构及其润湿性的影响。实验结果表明:低Q频下织构边界模糊，高Q频下边界清晰；随功率上升，织构边界膨胀严重，重铸区不断增大；加工次数与微织构深度近似成正比关系；随扫描速度增大，材料的去除率下降，材料残留明显；制备完成初期织构表面存在能量残留，使得疏水织构出现亲水特性。     

飞秒激光诱导硬质合金YG6表面累积效应

采用波长800nm的飞秒激光对硬质合金YG6表面进行多脉冲加工,利用光学显微镜测量微凹坑损伤形貌及损伤直径,研究了飞秒激光在不同能量密度和脉冲数下硬质合金YG6的损伤阈值和损伤直径的变化规律及其损伤机制.试验结果表明:硬质合金YG6的多脉冲损伤阈值随着脉冲数增加而降低,呈现明显的累积效应.试验得到了多脉冲飞秒激光加工YG6的损伤阈值、损伤直径与脉冲数及中心能量密度的定量关系,YG6多脉冲损伤阈值主要与脉冲数相关,由单脉冲损伤阈值和累积系数共同决定,试验得到YG6单脉冲损伤阈值为1.14±0.06J/cm2,累积系数为0.84±0.02.损伤直径主要与光束中心能量密度和脉冲数相关,由光束束腰半径,单脉冲损伤阈值和累积系数共同决定.试验采用多组平均功率和脉冲数对YG6进行烧蚀,验证了单脉冲损伤阈值和累积系数的可靠性.     

6H-SiC的飞秒激光超衍射加工

利用飞秒激光直写微纳加工平台, 对6H-SiC材料进行了突破衍射极限的微纳结构加工研究. 使用中心波长和脉宽分别为800 nm和130 fs的钛蓝宝石激光器和荧光倒置显微镜搭建了飞秒激光直写微纳加工平台, 研究了在不同的实验条件下对6H-SiC的光学加工情况, 采用扫描电子显微镜对加工结构进行表征. 通过分析不同的激光功率和不同的曝光时间等实验条件下加工的分辨率, 发现分辨率随着激光功率的减小而提高, 随扫描速度的增大而提高, 且能突破光学衍射极限. 最终获得125 nm的加工线宽, 并加工了加工线宽240 nm, 周期1.0 μm的线阵列. 研究结果为微机电系统(MEMS)的微器件设计开创了新的思路, 对发展MEMS器件具有重要意义. 关键词： 飞秒激光直写 超衍射加工 6H-SiC 微机电系统     

飞秒激光直写PMMA制备微流道的工艺技术研究

针对目前PMMA微流道加工质量差和效率低的问题, 对飞秒激光直写PMMA制备微流道的工艺技术进行了研究。通过实验分析了不同激光参数对微流道的宽度、深度、粗糙度、微流道两侧堆积物火山口高度的影响及变化规律。实验结果表明, 当激光扫描速度为20 mm/s时, 激光功率为0.5 W时, 微流道粗糙度较低且变化幅度不明显; 激光能量从0.5 W增加到0.75 W时, 微流道的宽度、深度与激光能量呈线性关系增加; 激光功率大于0.5 W时, 随着激光功率以及加工次数的增加, 微流道宽度、深度、粗糙度以及堆积物火山口的高度逐渐增加。经过计算得出, PMMA的烧蚀阈值为0.357 J/cm2。通过优化工艺参数, 制备出粗糙度较低、表面光滑、深度为16 μm的微流道芯片。     

微球透镜对亚波长表面结构的显微成像研究

为了研究微球透镜对亚波长物体的成像特性,利用直径为3.4μm的二氧化硅微球透镜对刻录蓝光光碟的亚波长表面结构进行了显微成像实验,观察了不同排列方式和液体浸没深度下微球透镜的成像特性。实验结果表明:微球透镜在不同浸没深度下对亚波长表面结构具有放大作用,放大率为1.2~1.8倍,并且通过微球透镜的密排列,可以获得更大的视场;浸没液体深度增大时,图像的放大率减小,视场增大。基于时域有限差分的电场仿真表明,微球透镜可以将光场汇聚成半高全宽为260nm,纵向可持续几个微米的高强度光区域,引起强的背景散射,从而获得普通光学显微镜不能分辨的亚波长表面结构图像。     

利用激光打标法制备侧面均匀发光聚合物光纤

研究了一种侧面均匀发光聚合物光纤(POF)的制备方法,采用激光打标技术在POF侧面制作变栅距(VLS)光栅型散射点,建立了激光打标VLS散射点模型,该模型由深度很浅的表面凹坑和纤芯内分布着散射颗粒的散射区组成。理论推导出散射点相对散射光功率和VLS栅距的计算公式,分析了散射点的散射光功率随凹坑深度和颗粒密度的变化规律,以及不同散射点凹坑深度和不同POF侧面发光相对出射度下VLS栅距的分布规律。结果表明散射点凹坑深度的微小变化(微米量级)对散射点的散射光功率和VLS栅距的影响很大。当散射颗粒密度N105 mm-3时,散射点散射光功率变化不大;但是当N105 mm-3时,散射光功率变化明显。理论计算了不同散射点凹坑深度和不同相对出射度的VLS栅距分布曲线,并且通过实验验证了理论结果的正确性。通过调节激光打标功率,实验得到了亮度均匀度高于90%的侧面发光POF。     

内燃机缸套内表面激光微造型数值模拟与实验研究

针对内燃机缸套-活塞环摩擦副系统,开展缸套内表面单脉冲同点间隔多次激光微凹腔和微沟槽的工艺实验和数值模拟研究,分析了激光功率、激光脉冲次数对45~#钢靶材表面微凹腔和微沟槽形貌的影响规律。研究结果表明,随激光功率的增加,微凹腔的深度增加幅度不大且趋于平缓,外沿金属残渣增多,光斑中心温度近似线性增加;增加激光脉冲次数,微凹腔深度增加显著,但金属熔液的重铸现象明显,表面加工质量下降;微沟槽深度和宽度随激光功率的增加都有所增加,且宽度的增幅较深度更为明显;相同工况条件下,仿真结果与实验结果趋势一致。     

全内反射显微技术探测亚表面缺陷新方法研究

亚表面缺陷的检测和去除对于提高光学元件的激光损伤阈值至关重要。结合全内反射显微技术和数字图像处理技术获得光学元件亚表面缺陷信息的新方法,利用显微镜系统的有限焦深,对亚表面缺陷沿深度方向扫描,可以获得不同离焦量下的散射图像,通过数字图像处理技术,建立缺陷散射图像清晰度评价值与离焦量的关系,通过清晰度曲线得到亚表面缺陷的深度位置及深度尺寸。模拟全内反射显微平台的成像过程,讨论微调焦过程中全内反射显微成像的特点。缺陷深度位置及深度尺寸的测量精度主要由载物台精密调焦机构的精度以及显微镜的焦深决定,一般可达微米量级。利用飞秒激光加工技术制备尺寸和位置已知的微结构,使用该方法准确获得了微结构信息,验证了该方法的有效性。     

Preparation and characterization of nano and microcrystalline ZnO thin films by PLD

Nano and microcrystalline ZnO thin films were prepared on glass substrates using pulsed laser deposition technique under a vacuum of 3 × 10⁻⁷ Torr at different laser power density. Composition analyses show that the films deposited at low laser power density have more structural defects than the film deposited at high laser power density. It confirms that the content of Zn in free-state decreased greatly at high laser power density. Atomic force microscopy analysis shows that the surface roughness of the deposited films increases with an increase in laser power density. X-ray diffraction analyses show that all the films are oriented along (0 0 2) direction independently on the laser power density applied. The structural quality increases with an increase in laser power density. It is due to the fact that the increase of laser power density leads to the enhancement of peak intensity. The increase of laser power density reduces the film transmission in the visible range of the spectra. The optical band gap value is found to be in the range from 3.42 to 3.39 eV. It shows that the optical band gap value decreases with an increase in laser power density. FTIR analysis shows that the hydrated oxide content in the deposited films decreases with an increase in laser power density.     

Peak-Power Instabilities of Laser Pulses Retroreflected by a Corner-Cube Retroreflector at Different Distances

In order to obtain the change in the return laser-pulse peak-power instability with the distance between two communication terminals in a free-space optical communication (FSO) asymmetric link, which uses a corner-cube retroreflector (CCR) and a high peak-power pulse laser, we present the peak power instability of laser pulses retroreflected by the CCR at different distances. The CCR bottom surface was a circle with a diameter of 1 in., and three mirrors of the CCR were coated with silver. The weather was cloudy with winds of Category 4. The distances from the transmitter to the CCR were 120, 1,550, 3,900, and 5,240 m. The laser emitted 100 laser pulses with a peak power of 5 MW at each distance. The results of the experiments show that the increase in both absolute and relative peakpower instabilities with the distance is approximately linear. The absolute peak-power instability is more than 58.7 mV and the relative peak-power instability is more than 11.8 % if the distance increases 1 km.     

光纤倏逝波型石英增强光声光谱技术

采用块状光学准直聚焦透镜组的传统石英增强光声光谱(QEPAS)技术存在体积难以缩减,结构稳定性不佳,无法适应空间狭小、振动复杂的特殊环境等缺点.基于此,将光纤倏逝波技术与QEPAS技术相结合,提出了一种新型微纳结构光纤QEPAS痕量气体检测技术.实验中,为了提高QEPAS系统信号幅值,优化了石英音叉与激光束的空间位置、激光波长调制深度,同时对比了两种不同共振频率的石英音叉,最终采用共振频率较低的30.720 kHz石英音叉作为声波探测元件,获得的检测极限为6.25×10~(-4)(体积分数),归一化噪声等效吸收系数为4.18×10~(-7)cm~(-1).W·Hz~(-1/2).     

Irradiation effects of CO2 laser parameters on surface morphology of fused silica

To understand the surface morphology evolution of fused silica induced by 10.6-μm CO2 laser irradiation at different parameters,this paper reports that optical microscopy,profilometry,and hydrophilicity tests are utilized to characterize the surface structure and roughness of the laser irradiated area. The results show that three typical surface morphologies and two typical hydrophilicity test images are observed at different laser powers and pulse durations. The correlations between surface temperature and surface morphology as well as hydrophilicity behaviours are presented. The different hydrophilicity behaviours are related to surface structures of the laser-induced crater and thermal diffusion area. The thermal diffusion length monotonously increases with increasing laser power and pulse duration. The crater width is almost determined by the laser beam size. The crater depth is more sensitive to the laser power and pulse duration than the crater width.     

On the effects of using CO2 and F2 lasers to modify the wettability of a polymeric biomaterial

Enhancement of the surface properties of a material by means of laser radiation has been amply demonstrated previously. In this work a comparative study for the surface modification of nylon 6,6 has been conducted in order to vary the wettability characteristics using CO₂ and excimer lasers. This was done by producing 50 μm spaced (with depths between 1 and 10 μm) trench-like patterns using various laser parameters such as varying the laser power for the CO₂ laser and number of pulses for the excimer laser. Topographical changes were analysed using optical microscopy and white light interferometry which indicated that both laser systems can be implemented for modifying the topography of nylon 6,6. Variations in the surface chemistry were evaluated using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analysis which showed that the O₂ increased by up to 1.5 at% and decreased by up to 1.6 at% for the CO₂ and F₂ laser patterned samples, respectively. Modification of the wettability characteristics was quantified by measuring the advancing contact angle, which was found to increase in all instances for both laser systems. Emery paper roughened samples were also analysed in the same manner to determine that the topographical pattern played a major role in the wettability characteristics of nylon 6,6. From this, it is proposed that the increase in contact angle for the laser processed samples is due to a mixed intermediate state wetting regime owed to the periodic surface roughness brought about by the laser-induced trench-like topographical patterns.     

316L不锈钢粉末光纤激光选区熔化特性

采用自行研制的光纤激光选区熔化快速成型设备,研究了选区激光熔化316L不锈钢粉末工艺参数、能量输入与样件致密度、表面形貌之间的关系以及微观组织特征。结果表明:扫描速度对成型效果影响最为显著;样件致密度随着激光能量密度提高有逐渐增大的趋势;能量密度作为选区激光熔化工艺的技术指标具有可操作性;表面形貌由激光功率与扫描速度比值所决定。深入探讨了能量输入、熔化凝固行为、激光功率与扫描速度比值与样件致密度、表面形貌的关系。结果表明:选区激光熔化凝固组织层内、层间熔合处为弧形,且为冶金结合,金相组织主要由柱状晶与等轴晶组成,层内靠近熔合线周围是柱状晶,而层间靠近熔合线附近主要是细小等轴晶,晶粒直径为1μm左右。     

Effects of 1064 nm laser on the structural and optical properties of nanostructured TiO2 thin film

TiO₂ thin film has been widely used as photoelectrode in dye-sensitized solar cells. It can also be used in quantum dot synthesized solar cells. Study of its effects in different spectrum of light is important for its use in solar cells. We have reported effects of 1064 nm laser on the surface morphology, structural and optical properties of nanostructured TiO₂ thin film deposited on glass substrates using sol-gel spin coating technique. Q-Switched Nd:YAG pulsed laser at various power densities is used in this study. Surface morphology of the film is investigated using X-ray diffraction (XRD) and atomic force microscopy technique. The XRD pattern of as deposited TiO₂ thin film is amorphous and after laser exposure it became TiO₂ anatase structure. Atomic force microscopy of the crystalline TiO₂ thin film shows that the grain size increases by increasing laser power density. The calculations of the band gap are carried out from UV/Visible spectroscopy measurements with JASCO spectrometer. For laser power density of 25 MW/cm² there is an increase in the transmission and it decreases at the value of 38 MW/cm² and band gap decreases with increasing laser power density. Photoluminescence spectra of the crystalline TiO₂ thin film indicate two broad peaks in the range of 415 and 463 nm, one for band gap peak (415 nm) and other for oxygen defect during film deposition process.     

Laser-based modification of wettablility for carbon fiber reinforced plastics

This paper presents a laser-based technique for surface preparation of carbon fiber reinforced plastics (CFRP) for bonded repair. Ablative and non-ablative treatment of the surface is produced by variation of laser power and the resulting surface energy determined by goniometric measurements. Wettability has been directly related to a calculated wetting envelope. The investigations show an additional major influence of the surface topography on the shear strength of the joint. The direction of the applied laser lines in relation to the fiber direction was identified as an essential influence for this roughness. A ns IR-laser demonstrates high potential for surface preparation as well as for selective ply removal. The laser prepared surfaces are examined through optical microscopy, scanning electron microscope (SEM), and contact angle measurements. The wettability studies show a significant increment in surface energy after laser treatment, in relation to non-treated as well as surface grinding samples.     

Performance analysis of an optical device for cylindrical flow visualizations

The performance of an optical device which allows a laser beam to be converted into a thin cylindrical light sheet is presented; a double conical reflector is associated with a focusing system. The adjustment possibilities of the optical parameters are related according to the Gaussian laser beam theory, sheet diameter and thickness, focusing distance, sheet field depth and power density. An example of the visualization in a Taylor-Couette flow is described.