Coating characterization in controlled surface temperature laser heat treating

An evaluation of coating performances in feedback controlled surface temperature laser heat treating has been made in terms of a simple energy balance model, by using a 500 W c.w. CO₂ laser system able to perform such a kind of heat treating. Three different types of coating (manganese phosphate, titanium dioxide and colloidal graphite) have been investigated. The experimental results show that very different maximum processing speeds are ensured by each coating, in spite of their quite similar percentage of absorbed laser power. This more complete characterisation can be used to improve the performances of the aforesaid technique, avoiding any failure in controlled surface temperature laser heat treating.     

Controlled surface temperature laser heat treating

The analysis and experimental procedure of a controlled temperature laser heat treating process are reported.Key features are the ease of predicting working results and the capability of getting on-line process diagnostics for use in a highly automated industrial environment.     

Metal surface temperature induced by moving laser beams

Whenever a metal is irradiated with a laser beam, electromagnetic energy is transformed into heat in a thin surface layer. The maximum surface temperature is the most important quantity which determines the processing result. Expressions for this maximum temperature are provided by the literature for stationary cases. In practice, however, moving beams are of more importance.Based on a fast numerical algorithm which allows calculation of the induced temperature profile, the maximum surface temperature for stationary and moving laser beams is calculated. Next, two types of approximating functions are presented relating the scanning speed to the maximum surface temperature. Using dimensionless numbers, the results can be applied to different materials.     

The application of arbitrary incidence laser beams heat treatment temperature field calculation formulas

Based on the calculation formulas of heat treatment temperature field for an arbitrary incident laser intensity distribution, the transformation intensity distribution of CO2 laser beam passing an integrating mirror is studied theoretically and experimentally. The derived formulas are applied in laser heat treatment research which is transformed by optical system, and the theoretical calculation results are compared with experimental results. It is shown that the formulas can be used to calculate the laser heat treatment temperature field accurately, and the calculation speed is obviously faster than the numerical calculation methods with the same precision. The calculation software can be used to select proper experiment parameters.     

Numerical calculations of temperature distribution of double layer metallic surface treated by laser beams

A mathematical model of laser beam treatment of double layer alloys (Ni/Fe, Al/Fe and Cr/Fe systems) describing the effect of laser beam on different physical and geometrical parameters of coated layer system has been adapted. The numerical solutions of the non-homogeneous heat-transport differential equation could estimate the temperature of the treated region.The suggested model allows investigation of the temperature distribution as a function of treated surface and laser parameters. The physical parameters of the treated materials were taken as functions of temperature due to the change in the temperature of the treated double layer materials.     

固体棒状热容激光器的热分析

计算出固体棒状热容激光器在不同散热边界条件下的温度分布和随时间的演变,与实验测量的结果进行了对比。计算结果表明：激光器工作在热容模式时,不同散热边界条件下激光介质内的温度分布在激光发射期间区别不大,激光发射期间,激光介质内的温度分布主要取决于泵浦光的吸收。但是散热过程中的不同散热边界条件下温度分布演化大不相同,此时的温度分布主要取决于散热边界条件。     

固体棒状热容激光器的热分析

 计算出固体棒状热容激光器在不同散热边界条件下的温度分布和随时间的演变,与实验测量的结果进行了对比。计算结果表明：激光器工作在热容模式时,不同散热边界条件下激光介质内的温度分布在激光发射期间区别不大,激光发射期间,激光介质内的温度分布主要取决于泵浦光的吸收。但是散热过程中的不同散热边界条件下温度分布演化大不相同,此时的温度分布主要取决于散热边界条件。     

Hybrid fuzzy logic control of laser surface heat treatments

This paper presents an advanced hybrid fuzzy logic control system for laser surface heat treatments, which allows to increase significantly the uniformity and final quality of the obtained product, reducing the rejection rate and increasing the productivity and efficiency of the treatment. Basically, the proposed hybrid control structure combines a fuzzy logic controller, with a pure integral action, both fully decoupled, improving the performances of the process with a reasonable design cost, since the system nonlinearities are fully compensated by the fuzzy component of the controller, while the integral action contributes to eliminate the steady-state error.     

The use of enhanced surface in flow boiling heat transfer in a rectangular minichannel

The results of flow boiling heat transfer in a 1-mm-deep vertical minichannel are presented. The heating element for an FC-72 laminar flow in a minichannel is a single-sided enhanced foil with various depressions; liquid crystal thermography was used for measuring temperature distribution of the foil. The void fraction and vapor quality were determined for some cross-sections of two-phase flow images. Results presented in the form of boiling curves were analyzed. Both typical and untypical shapes of boiling curves were found. The suitability of classical methods of two-phase pressure drop determination using experimental verification was confirmed.     

用空间频率参量研究激光束特性

本文提出了一种新的方法,用空间频率参量解亥姆霍兹微分方程来获得激光束特性的解析数学描述,并从空间频率参数出发定义了光束束散角和激光束腰斑最小极限值。与用衍射积分方程所得解相比较,结果一致。     

评估固体激光器对流换热系数的方法

 为提高固体激光器的热管理效果,提出了一种使用316L不锈钢片代替激光晶体评估固体激光器表面对流换热系数的方法。在低冷却水温的条件下,使用快响应热电偶对替代片和出口水流的动态温度进行测量,应用有限元方法计算不同对流换热系数下替代片的动态温度,讨论了对流换热系数对重频大能量激光器热效应的影响。通过寻找测量值和计算值的最小方差,得到该冷却结构下的激光器表面对流换热系数为3 500 W·m^-2·K^-1。     

评估固体激光器对流换热系数的方法

为提高固体激光器的热管理效果,提出了一种使用316L不锈钢片代替激光晶体评估固体激光器表面对流换热系数的方法。在低冷却水温的条件下,使用快响应热电偶对替代片和出口水流的动态温度进行测量,应用有限元方法计算不同对流换热系数下替代片的动态温度,讨论了对流换热系数对重频大能量激光器热效应的影响。通过寻找测量值和计算值的最小方差,得到该冷却结构下的激光器表面对流换热系数为3 500 W·m-2·K-1。     

fs激光在靶背表面产生的质子束成丝

 介绍了利用3TW/60fs钛宝石超短超强激光与20μm铜薄膜靶相互作用的实验。实验观测到质子束的角分布随激光功率密度有所变化。在较高的功率密度（～1×10¹⁸ W/cm²）时，观测到环状的质子束分布，发散角较大。在较低的激光功率密度（～2×10¹⁷ W/cm²）时，质子束发散角减小，质子束出现成丝现象。质子束的角分布实际上反映了从靶前输运到靶背的超热电子电流横向分布。在输运过程中，由于Weibel不稳定性会使超热电子电流出现空心化并最后破裂成丝。     

fs激光在靶背表面产生的质子束成丝

介绍了利用3TW/60fs钛宝石超短超强激光与20μm铜薄膜靶相互作用的实验。实验观测到质子束的角分布随激光功率密度有所变化。在较高的功率密度（～1×1018 W/cm2）时,观测到环状的质子束分布,发散角较大。在较低的激光功率密度（～2×1017 W/cm2）时,质子束发散角减小,质子束出现成丝现象。质子束的角分布实际上反映了从靶前输运到靶背的超热电子电流横向分布。在输运过程中,由于Weibel不稳定性会使超热电子电流出现空心化并最后破裂成丝。     

激光脉冲波形对烧蚀Si靶表面温度的影响

利用双温方程对激光烧蚀Si靶的过程进行了数值模拟,并结合合适的初始条件和边界条件,研究了在飞秒、皮秒激光作用下,脉冲波形（矩形、梯形、三角形和高斯形）对Si靶表面载流子和晶格温度分布的影响。结果表明：激光功率密度是影响载流子温升的主要因素,矩形脉冲激光烧蚀Si靶表面载流子的峰值温度最高,而高斯分布的脉冲引起靶面载流子峰值温度最低。可见,激光脉冲波形对Si靶表面载流子的温度分布具有重要影响。所得结果可为制备高质量的薄膜提供理论依据。     

激光脉冲波形对烧蚀Si靶表面温度的影响

利用双温方程对激光烧蚀Si靶的过程进行了数值模拟,并结合合适的初始条件和边界条件,研究了在飞秒、皮秒激光作用下,脉冲波形(矩形、梯形、三角形和高斯形)对Si靶表面载流子和晶格温度分布的影响。结果表明:激光功率密度是影响载流子温升的主要因素,矩形脉冲激光烧蚀Si靶表面载流子的峰值温度最高,而高斯分布的脉冲引起靶面载流子峰值温度最低。可见,激光脉冲波形对Si靶表面载流子的温度分布具有重要影响。所得结果可为制备高质量的薄膜提供理论依据。     

Nonresonant quadrupolar second-harmonic generation in isotropic solids by use of two orthogonally polarized laser beams

We demonstrate an experimental technique for isolating and enhancing quadrupolar second-harmonic generation in isotropic materials by using two orthogonally polarized laser beams that create wavelength-scale, forward-radiating gradients in the second-harmonic polarization.     

Interferometric scanning of laser beams

A new beam deflection technique is based on modulating the optical transmission characteristics of a modified Fabry-Perot interferometer. Electro-optically changing the interferometer length leads to fast high resolution scanning of the transmission fringe. Experiments have been conducted using the 4880 Å argon laser line with an interferometer containing a LiNbO₃ crystal.