纳秒级脉冲激光诱导Zn掺杂过程中GaN/Al2O3材料的温度分布及热形变解析分析

分析了纳秒级脉冲激光作用下GaN的激光诱导Zn的掺杂过程.利用简化的一维模型，给出一种比较直观的脉冲激光辐照下GaN/Al₂O₃材料温度分布的解析形式，得到了GaN材料表面温度与激光辐照时间的关系以及材料形变与深度的关系.在激光脉冲作用时，GaN材料表面的温度与辐照时间的平方根成正比.脉冲过后，材料温度分布梯度和热形变分布随深度发生变化，接近表面的温度梯度最大，热形变量也最大.而在连续脉冲作用时表面的温度呈锯齿状不断升高. 关键词： 激光诱导 2O₃')" href="#">GaN/Al₂O₃ 温度分布 热形变     

纳秒级脉冲激光诱导Zn掺杂过程中GaN/Al2O3 材料的温度分布及热形变解析分析

分析了纳秒级脉冲激光作用下GaN的激光诱导Zn的掺杂过程.利用简化的一维模型,给出一种比较直观的脉冲激光辐照下GaN/Al2O3材料温度分布的解析形式,得到了GaN材料表面温度与激光辐照时间的关系以及材料形变与深度的关系.在激光脉冲作用时,GaN材料表面的温度与辐照时间的平方根成正比.脉冲过后,材料温度分布梯度和热形变分布随深度发生变化,接近表面的温度梯度最大,热形变量也最大.而在连续脉冲作用时表面的温度呈锯齿状不断升高.     

1.06μm连续激光辐照TiO_2/SiO_2/K_9薄膜元件温升规律研究

利用1.06μm连续激光在不同强度下辐照TiO2/SiO2/K9薄膜元件,实验中用红外热像仪测量激光辐照在TiO2/SiO2/K9元件表面引起的温升随时间的变化,通过数据处理,获得激光辐照区域最高温度随辐照时间的增加而增加。同时,给出材料温升随材料发射率的变化关系。并用程序模拟不同激光强度下薄膜温度场的分布,通过实验测量数据校正数值模拟计算结果,给出TiO2/SiO2/K9薄膜元件温度随激光辐照强度和辐照时间的变化规律。并且获得在薄膜厚度方向:薄膜表面温度最高,基底与薄膜接触处温度最低;沿径向:激光辐照中心温度最高,边沿温度最低。     

采用泵浦探测技术研究VO2薄膜相变特性

为研究纳秒激光作用下的VO₂薄膜的相变特性,采用泵浦-探测技术进行实验。首先,利用直流磁控溅射法制备VO₂薄膜,经X射线衍射（XRD）和原子力显微镜（AFM）分析表明样品质量较高。然后,测量VO₂薄膜在波长532 nm处的透过率随温度的变化情况,发现透过率随温度升高由32%上升到37%,与红外波段完全相反。在此基础上,选择1 064 nm泵浦光和532 nm探测光研究激光参数中能量密度和重频对VO₂薄膜相变特性的影响,同时结合ANSYS有限元软件对纳秒激光作用下VO₂薄膜的单脉冲温升情况进行分析。结果表明：VO₂薄膜在大于30 mJ/cm²的纳秒激光能量密度作用下,单脉冲温升可达相变温度,最小相变响应时间在14 ns左右。进一步提高纳秒激光能量密度,其相变响应时间略有增加但变化不大。在100 Hz以内改变纳秒激光重频对VO₂薄膜的相变响应基本无影响。VO₂薄膜的相变恢复时间随着纳秒激光能量密度的增大而呈自然指数增加,其变化过程与基底材料和纳秒激光参数密切相关。因此,可以通过优化VO₂薄膜基底材料参数提高其激光防护效果。     

1.06 μm连续激光辐照TiO2/SiO2/K9薄膜元件温升规律研究

利用1．06μm连续激光在不同强度下辐照TiO2／SiO2／K9薄膜元件,实验中用红外热像仪测量激光辐照在TiO2／SiO2／K9元件表面引起的温升随时间的变化,通过数据处理,获得激光辐照区域最高温度随辐照时间的增加而增加。同时,给出材料温升随材料发射率的变化关系。并用程序模拟不同激光强度下薄膜温度场的分布,通过实验测量数据校正数值模拟计算结果,给出TiO2／SiO2／K9薄膜元件温度随激光辐照强度和辐照时间的变化规律。并且获得在薄膜厚度方向：薄膜表面温度最高,基底与薄膜接触处温度最低;沿径向：激光辐照中心温度最高,边沿温度最低。     

光斑尺寸对连续激光辐照铝合金温度响应影响研究

为了探究不同光斑尺寸连续激光辐照6 061铝合金的温度响应及热致损伤问题,基于ANSYS有限元软件建立了激光辐照下的三维物理模型;使用不同的激光参数进行激光辐照实验,根据所采集的温度和前表面散射光强度数据,反演计算了靶材在激光辐照过程中吸收率的动态变化;最后,利用优化后的模型分析了不同光斑尺寸下,激光辐照靶材的温升特点。研究结果表明:在1 000 W/cm~2的激光辐照条件下,材料的吸收率随着温度的升高而升高;由于激光加载的局域化特征,横向热扩散影响纵向温升,光斑足够大时该影响变小,这与其热扩散长度有关;对于4 mm厚的6 061铝合金材料,当光斑尺寸大于10 cm时,光斑影响可以忽略,靶材背表面发生熔融损伤时间阈值保持2.6 s不变。     

物理参数变化对短脉冲激光激励温度场的影响

 为研究多物理参数（耦合系数、电子热导率、电子热容、晶格热容）同时随温度变化对短脉冲激光辐照金属材料产生温度场分布的影响,基于双温耦合理论,建立了短脉冲激光辐照金属材料金的加热过程的有限元求解模型。在同时考虑脉冲激光的空间、时间分布和多参数同时随温度变化的情况下,得到短脉冲激光辐照金属材料金激励产生的温度场二维瞬态分布,并进一步比较了多物理参数同时随温度变化和采用室温物理参数两种情况下温度场分布的区别。数值结果表明：多物理参数同时随温度变化使电子温度和晶格温度的上升变快,最大值变大,而且使得材料中激光穿透直接辐照到的区域温度变高。     

0.53 μm毫秒脉冲激光对GaAs热分解损伤特性

针对波长0.53 m的毫秒脉冲激光辐照GaAs的表面热分解损伤问题,建立了二维轴对称热传导模型,在考虑材料的热物性参数随温度变化的基础上,采用有限元法模拟了材料的瞬态温度场,得到了温度场分布特征及其随时间的变化规律,给出了材料表面发生热分解损伤阈值曲线。数值结果表明:毫秒脉冲激光对GaAs作用时,热传导影响着激光作用全过程,对应的损伤机理主要为热损伤;在激光作用下,被作用表面中心处温度最高,并且首先发生热分解损伤;随着作用激光能量密度的增加,GaAs表面发生热分解损伤的时刻不断提前。     

纳秒脉冲激光沉积薄膜过程中的烧蚀特性研究

研究了高能短脉冲激光薄膜制备的整个烧蚀过程.首先建立了基于超热理论的烧蚀模型，然 后利用较为符合实际的高斯分布表示脉冲激光输入能量密度，给出了考虑蒸发效应不同阶段 的烧蚀状态方程.结合适当的边界条件，以Si靶材为例，利用有限差分法得到了靶材在各个 阶段温度随时间和烧蚀深度的演化分布规律及表面蒸发速度与烧蚀深度在不同激光辐照强度 下随时间的演化规律.结果表明，在脉冲激光辐照阶段，靶材表面的蒸发效应使得靶材表面 温度上升显著放缓；在激光辐照强度接近相爆炸能量阈值时，蒸发速度与蒸发厚度的变化由 于逆流现象将显著放缓.还得到了考虑了熔融弛豫时间及蒸发效应的固-液界面随时间的演化 方程，这一结论较先前工作更具有普适性. 关键词： 脉冲激光烧蚀 热流方程 温度演化 有限差分法     

CO2激光局域辐照对熔石英损伤特性的影响

研究了CO₂激光局域辐照对熔石英损伤特性的影响, 发现当辐照中心温度较低时(1139 K), 辐照对损伤阈值没有明显影响, 但辐照中心温度较高时(1638 K), 辐照对损伤阈值有明显的影响, 损伤阈值随距离辐照中心间距的增大而减小, 在残余应力产生光程差最大处附近, 损伤阈值降到最小, 随着与辐照中心间距的进一步增加, 损伤阈值略有上升. 对导致此现象的原因做了分析. 由于残余应力的存在, 在辐照中心发生再损伤产生的裂纹后, 裂纹先沿径向扩展, 在残余应力产生光程差最大处附近, 裂纹转而向切向扩展, 这可能与径向和环向张应力随半径的变化有关. 在采用热处理炉退火消除残余应力时, 必须注意元件的洁净处理, 否则退火会出现析晶现象, 对损伤阈值和透射率造成不良影响. 关键词： 2激光局域辐照')" href="#">CO₂激光局域辐照 熔石英 损伤特性     

连续CO2激光辐照加热不锈钢时的 反常温度涨落特性

The temperature fluctuation of the stainless steel irradiated by a CW CO₂ laser is studied. In the experiment, the temperature fluctuation and the temperature rise is measured by the infrared thermal imagers. It is found that the maximum amplitude of the temperature fluctuation is kept constant with the increase of the laser heating time;this is different from aluminum, low carbon steel, epoxylite and polymethylmethacrylate. This characteristic of the stainless steel is determined by the variance of thermal conductivity and thermal diffusivity with the increase of temperature. A thorough study of the effects of the material thermal properties on the temperature fluctuation is needed.     

The influence of substrate temperature on femtosecond laser micro-processing of silicon,stainless steel and glass

We report the influence of substrate temperature on femtosecond laser ablation of silicon, stainless steel, and glass. Remarkable decrease in surface roughness was observed under high substrate temperature for silicon and stainless steel. While the ablation efficiency of glass as a typical wide band-gap material is scarcely altered at 900 K, the efficiency for stainless steel as a conductor apparently increased about 20% accompanied to the elevation of substrate temperature from 300 to 900 K. Silicon wafer results in slight increase of the ablation efficiency with decreasing the ablation threshold. Considering that the melting temperature of glass is much lower than those of silicon and steel, the observations from this work suggests that the material ablation caused by the ultrafast laser irradiation could not be explained in term of only laser-induced thermal excitation.     

Mechanism of and method to avoid discoloration of stainless steel surfaces in laser cleaning

2 O₃. Based on Auger Electron Spectroscopy analyses and optical microscopic observations, γ-Fe₂O₃ and Fe₃O₄ are formed on the stainless steel surface in laser cleaning in the air. Since laser can induce high temperature rise in stainless steel surfaces, the above phenomenon can be explained by a thermochemical reaction between oxygen in the air and the stainless steel. With increasing laser fluences, the temperature rise in the irradiated area of stainless steel surface increases, which enhances oxygen diffusion into the surface and oxidation reaction within the irradiated area. In order to avoid discoloration of stainless steel surfaces, a vacuum system was used to reduce the oxidation reaction between oxygen and stainless steel. Received: 7 June 1996/Accepted: 30 September 1996     

Study of influences of laser power fluctuation on thermogram of the material

The effects of the laser beam instability on the temperature of the material are studied in this paper. The fluctuation of the temperature not only relates to the laser beam instability, but also correlates with the thermal conductivity, the thermal diffusivity, the emissivity, the laser–solid interaction time, and the laser spot diameter. The temperature fluctuation of the aluminum, the polymethylmethacrylate, the epoxylite, and the low carbon steel is measured by the infrared thermal imagers (HWRX··) to determine validity of the theory prediction. It is found that the theoretical prediction is in good agreement with the experimental results. Besides, the maximum amplitude of the temperature fluctuation is calculated and how to control the temperature fluctuation is discussed. The results show that the temperature fluctuation in the laser–solid interaction is of importance in practice.     

Fiber laser welding of austenitic steel and commercially pure copper butt joint

The fiber laser welding of austenitic stainless steel and commercially pure copper in butt joint configuration without filler or intermediate material is presented. In order to melt stainless steel directly and melt copper via heat conduction a defocused laser beam was used with an offset to stainless steel. During mechanical tests the weld seam was more durable than heat affected zone of copper so samples without defects could be obtained. Three process variants of offset of the laser beam were applied. The following tests were conducted: tensile test of weldment, intermediate layer microhardness, optical metallography, study of the chemical composition of the intermediate layer, fractography. Measurements of electrical resistivity coefficients of stainless steel, copper and copper–stainless steel weldment were made, which can be interpreted or recalculated as the thermal conductivity coefficient. It shows that electrical resistivity coefficient of cooper–stainless steel weldment higher than that of stainless steel. The width of intermediate layer between stainless steel and commercially pure copper was 41–53 µm, microhardness was 128–170 HV_0.01.     

Optical properties of a new IR converter for laser beam analysis

This work presents the temporal and spacial resolution of a new infrared (IR) converter based on thermal radiation emission. Using this converter, it is possible to measure the intensity distribution of laser beams with a wavelength between 1 and 20 μm. For this purpose, the laser radiation (for example, 10.6 μm) is converted into a wavelength coverage of 800–1100 nm. In the actual converter thin metal foils provide the basis of this method. The metal foils are heated to a temperature of 600–800 K. The emitted radiation of the foils defers into the near-infrared (NIR) area, thus enabling detection by camera systems based on silicate. Additional heat input of the laser results in a local temperature increase, and then the increase in radiation intensity can be measured. Typical thicknesses of converter metal foils are <5μm. Foil materials with a low thermal conductivity, good absorption of the measured laser beams, and a high melting temperature are particularly suitable. These parameters are well shown by using stainless steels, such as INOX (stainless steel 1.4310 CrNi steel). Using this material, it is possible to gain a maximum spatial resolution of 250 μm and a temporal resolution of 12.5 Hz, by a measurement range from 1 to 100 W/cm². The maximum measured intensity is 125 W/cm².     

脉冲强激光辐照下材料响应的非傅里叶效应

 研究了在多脉冲强激光辐照下靶材的热传导与热冲击特性。基于非傅里叶导热定律和热弹性理论,推导出多脉冲激光辐照下靶材温度场和热应力场的解析式;结合适当的边界条件,以不锈钢靶材为例,利用有限差分法和Matlab计算得到了多脉冲强激光辐照下靶材内部过余温度随时间和深度演化情况以及内部热应力的演化规律。计算结果表明：多脉冲激光辐照下靶材热响应在离边界不同截面处温度波形变化出现延迟性,其滞后性能与弛豫时间有关;非傅里叶解中应力波的波前十分陡峭,具有明显的热冲击性。     

激光输出不稳定性对激光与物质热作用的影响

研究了激光与物质相互作用中激光输出不稳定性对材料中温度场颁的影响以及减少这种影响的途径。首次在激光热传导方程中引入噪声项,推导了噪声影响下该激光热传导方程的解。研究发现,温度场的分布受噪声的影响,材料表面温度的涨落较大,而材料的深处涨落较小;温度场的涨落还和激光加热的过程有关,随激光加热时间的增长,温度场的涨落增大。此外,材料的热传导系数、热扩散率和发射率均对温度场的涨落有影响。文中还提出了减小激     

激光扫描阵列结构增强不锈钢与塑料的连接强度

本文采用光纤激光器在不锈钢表面上制备圆形阵列结构来增强不锈钢与塑料的连接强度。研究了激光制备的圆形阵列结构参数以及连接参数对不锈钢与塑料连接强度的影响。结果表明,不锈钢表面经过激光扫描构形处理后能显著提高不锈钢与塑料的连接强度,在压力作用下,熔融塑料渗入激光构造微孔形成的机械互锁是增强不锈钢与塑料连接强度的主要机制。激光构形后不锈钢表面上的毛刺高度、数量以及覆盖率对连接接头的连接强度有重要影响。毛刺高度为10~20μm,毛刺数量占比Tm小于14.82%时,不锈钢与塑料在连接面处断裂,剪切力随着Tm的增加而增加;当Tm值高于14.82%时,在塑料处断裂,且剪切力数值在塑料的平均拉伸断裂力(950 N)上下浮动。不锈钢与塑料连接接头断裂于塑料处时所对应的最小覆盖率为38.5%,此时剪切力为900 N。此外,激光扫描处理过程中不锈钢与塑料连接的温度与压力对连接强度有重要影响,在加热温度为400℃时,不锈钢与塑料连接接头的剪切力最强;当压力为75 kN时,不锈钢与塑料连接接头的剪切力最强。     

Gd0.55Sr0.45MnO3薄膜光诱导电阻变化特性研究

分别采用固相反应和脉冲激光沉积的方法制备了电荷-轨道有序态锰氧化物Gd_0.55Sr_0.45MnO₃块材和多晶薄膜, 研究了薄膜在光诱导作用下的电阻变化特性. 实验结果表明该薄膜在整个测量温度范围内表现出了半导体型导电特性. 利用变程跳跃模型拟合电阻温度关系可知, 其电荷有序态转变温度为70 K. 激光作用致使薄膜电阻减小, 当激光功率度为40 mW/mm²时, 最大光致电阻相对变化值可达99.8%, 且在8 s的时间内达到了平衡态, 温度对其影响很小; 当激光功率度为6 mW/mm²时, 获得的最大光致电阻相对变化值为44%, 而且时间常数随温度的升高而增大, 这主要是由于光诱导和热扰动共同作用的结果.