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.     

The use of plane-polarized beams in controlled surface temperature laser heat treating

Plane-polarized CO₂ laser beams can be successfully employed in controlled surface temperature laser heat treating in order to improve the coupling between radiation and steel. The coupling efficiency has been quantitatively determined by means of a simple energy balance model, by using a medium-power CO₂ laser. In this way, the angle at which the best coupling can be obtained has also been singled out. Moreover, some heat treatments performed with a high power laser beam obliquely impinging on medium carbon steel samples have confirmed that controlled surface temperature laser heat treating can be completely free of the problems concerning the use of coatings generally employed.     

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。     

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.     

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.     

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。     

Room temperature continuous wave visible vertical cavity surface emitting laser

Visible VCSEL laser operated at room temperature continuous wave has been achieved by H+ implants using tungsten wires as an implantation mask. The laser wavelength is 650 nm, and the maximum output without heat-sink exceeds 85 W at CW operation. We also calculated the thermal resistance of the device.     

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。     

解析计算半导体激光器列阵的热沉温升

通过解热传导方程得到了半导体激光器列阵的热沉温升分布的解析表达式,并利用该解析式得到了热沉的温升分布图。分析了对流换热传热系数对上下表面温升的影响,当对流换热传热系数增大到某个值后,上下表面的温差变化很小,而温升随该系数的增大而降低,所得的结果与用有限元法算得的并经过实验验证的结果基本上是一致的。     

解析计算半导体激光器列阵的热沉温升

 通过解热传导方程得到了半导体激光器列阵的热沉温升分布的解析表达式,并利用该解析式得到了热沉的温升分布图。分析了对流换热传热系数对上下表面温升的影响,当对流换热传热系数增大到某个值后,上下表面的温差变化很小,而温升随该系数的增大而降低,所得的结果与用有限元法算得的并经过实验验证的结果基本上是一致的。     

High resolution laser beam induced current focusing for photoactive surface characterization

The micro-characterization of several surface properties of the solar cells can be accomplished using high-resolution laser beam induced current images. For obtaining these images, a very precise laser beam focusing on the photoactive surface is required. For this purpose, a methodology for obtaining the best focalization associated to the maximum of a peak curve has been developed. In this paper, a data set, obtained from the inner photoconversion properties of the system, has been evaluated with three different numerical analysis techniques: (a) derivative, (b) length and (c) Fourier Transform, in order to get the finest possible peak distribution. Then, an amount of 13 analytical peak curves using the Levenberg Marquardt algorithm to find the best curve that adjusts the data distribution have been analyzed.     

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.     

Silicon substrate temperature effects on surface roughness induced by ultrafast laser processing

We report the effect of substrate temperature (T_sub) in the range 300-900 K on the surface roughness of silicon wafer resulted from femtosecond laser ablation. The surface roughness observed at the laser fluences less then 0.3 J/cm² increases with increasing T_sub. However, the surface roughness decreases with increasing T_sub for the laser fluences between 0.5 and 1.0 J/cm². If the laser fluence is higher than 2.0 J/cm², the surface roughness is independent of T_sub. The effect of T_sub on the surface roughness can be understood in terms of the temperature dependence of optical absorption coefficient of silicon substrate, which eventually alters a mechanism underlying the fs-laser-material ablation process between optical penetration and thermal diffusion processes.     

Combined laser calorimetry and surface thermal lens technique for optical coating characterization

A combined laser calorimetry (LC) and surface thermal lens (STL) technique with a continuous-wave (cw) modulated excitation is developed for characterizing the absorption properties of optical coatings. LC and STL signals are simultaneously obtained with highly reflective coating samples irradiated at 1064 nm. With a modulated irradiation power of 2.6 W, the limits of absorptance detection for the LC and STL signals are approximately 1.2×10^-6 and 0.5×10^-6, respectively. The influences of different excitation parameters (modulation frequency, excitation-beam power and irradiation time) on the absorptance measurements are experimentally analyzed. The applicability of the combined LC and STL technique to the investigation of the laser-induced absorption changes of optical coatings in an absolute absorptance scale is demonstrated. PACS 42.87.-d; 78.20.-e     

Beam combining of a high-power laser diode bar on a temperature gradient heat sink

A new wavelength beam combining technique for a high-power laser diode bar by using a temperature gradient heat sink has been proposed. The thermal controlling principle of the temperature heat sink has been discussed. It has been proved by experiment that the linear temperature distribution, which generates linear wavelength spread of the output beams from a LD bar, can be obtained by introducing a temperature gradient heat sink and the output beams can be focused into a relative small spot by using the Czerny-Turner beam shaping system.     

Low temperature synthesis of SiC films by vacuum laser ablation and their characterization

Thin films of silicon carbide were grown on Si(100) substrate by pulsed laser ablation of powder-pressed target. The influence of substrate temperature on both structure and surface morphology of SiC films was studied by scanning electron microscopy, X-ray diffraction, and IR spectroscopy.     

Determination of temperature distribution in laser welded heat exchangers with the aid of finite element methods

The determination of the thermal histories in a tube-plate combination when welded with a high intensity heat source is discussed in this paper. The influence of the geometry of the plate and the use of nitrogen gas during the welding process on the thermal histories is shown. With the thermal histories known, the distortion due to thermal stresses could be determined.