厚硅片的高速激光切片研究

基于激光切片原理的分析,给出了厚硅片的高速激光切片方法,采用平凸腔补偿工作物质的热透镜效应,利用Nd∶YAG棒本身的自孔径选模作用,获得了光束质量因子M²等于4.19的50 W 1.064 μm激光输出。选取合适的扩束倍数、重复频率和出气孔直径,当切割0.75 mm厚的硅片时,切片速度达400 mm/min;当切割两层叠放的0.75 mm厚的硅片时,切片速度达到100 mm/min。切片的切口光滑,切缝较窄,重复精度高,切片质量好,达到用传统方法难以达到的切片效果。     

Process Characterisation of Pulsed Nd:YAG Laser Seam Welding

A wide range of pulsed laser welding parameters was identified. These include average peak power density (APPD), peak power, mean laser power, traverse speed, pulse repetition rate, duty cycle, pulse energy, spot size, and pulse duration. The type of laser beam temporal pulse shape studied was a rectangular power pulse. The effects of pulsed laser welding parameters on heat flow, weld dimension, and weldability are investigated. The study shows that weld quality is principally affected by APPD, mean power, and traverse speed, of which APPD is the most critical process parameter. A processing map containing the APPD effects is constructed as a guide for producing good welds.     

准基模纯风冷激光二极管泵浦Nd∶YAG激光器

介绍一种纯风冷激光二极管泵浦的脉冲Nd∶YAG激光器,单脉冲能量250mJ,重复频率25Hz,脉冲宽度7ns,光光转换效率13.6%。激光器输出为准基模,垂直和水平方向的M2值测量结果分别为2.81和4.09。同样结构下将风冷系统换成风冷水冷结合方式,激光器脉冲能量345mJ,重复频率提高到50Hz,光光转换效率上升为15.2%。两种形式的激光器连续工作时间5min,并进行了高温+55℃和低温-25℃的环境试验。     

Surface texturing by pulsed Nd:YAG laser

Introducing specific textures on a tribological surface can contribute to friction reduction in sliding contacts. In the present paper, a pulsed Nd:YAG laser emitting at 1064 nm, was used against 100Cr6 steel samples in order to produce well-defined surface micro-pores, which can act as lubricant reservoirs, micro-hydrodynamic bearings as well as traps for wear debris. Due to the high flexibility of the laser system, structural features such as shape, size, density and depth can be varied easily by changing the laser parameters. To optimize the parameters of the laser surface texturing process, an investigation was performed using different pulse numbers, various pulse energies and two different modes (single- and multi-mode). The microtextures were characterized with optical microscopy, scanning electron microscopy (SEM) and by topography techniques. The relationship between the laser processing parameters and qualitative and quantitative profile of the micro-pores was studied. Tribological testing of laser textured surfaces was performed in a low frequency–long displacement reciprocating sliding wear tester under boundary lubrication and results compared to un-textured case. Tribological comparison of textured, textured and lapped, and untextured surfaces shows only minimal influence of texturing for contact conditions investigated.     

垂直腔面发射激光端面泵浦的高能量调Q Nd:YAG激光

采用垂直腔面发射激光端面泵浦Nd∶YAG获得了高能量的1 064 nm调Q激光输出。与边发射半导体激光相比,垂直腔面发射激光具有各向发散角相同、波长随温度漂移小等优点,更适合用作泵浦源以产生高效率、结构紧凑的激光。泵浦能量为200 mJ时,产生了最高45 mJ的1 064 nm激光输出,光光转换效率达到22.5%,激光脉宽为8 ns,发散角为1.2 mrad。基于模拟计算优化了Nd3+掺杂浓度,通过采用低浓度的Nd∶YAG晶体减小泵浦端面增益,从而有效抑制了影响调Q激光能量提高的自激振荡,为获得高能量的端面泵浦调Q激光输出提供了有效的技术手段。     

Changes in nail keratin observed by Raman spectroscopy after Nd:YAG laser treatment

Lasers and photodynamic therapy have been considered a convergence treatment for onychomycosis, which is a fungal infection on the nail bed and nail plate. Laser therapies have shown satisfactory results without significant complications for onychomycosis; however, the mechanism of clearing remains unknown. In this work, we investigated changes in the chemical structure of nail keratin induced by Nd:YAG laser using Raman spectroscopy. Toe nails with onychomycosis were treated with 1064 nm Nd:YAG laser. After laser treatment, the disulfide band (490–590 cm^?1) of nail keratin was rarely observed or was reduced in intensity. The amide I band (1500–1700 cm^?1) also showed changes induced by the laser. The α‐helical (1652 cm^?1) structures dominated the β‐sheet (1673 cm^?1) in nontreated nail, but the opposite phenomenon was observed after laser treatment.     

染料调Q的Nd3+:YAG激光器偏振性测试

为了确定染料调Q的Nd3+:YAG激光器发射的单次激光脉冲的偏振性,利用偏振分束立方体和双通道激光能量计,实验测量了激光脉冲经偏振分束后P偏振光和S偏振光的能量比,分析总结了激光器的偏振性.结果表明:激光器偏振性个体差异很大,不存在统一性;每一台激光器都有各自的偏振性,同一台激光器前后发射的激光脉冲的偏振性可能一致,也可能变化较小,也可能完全随机.产生偏振性的具体原因有待进一步研究.     

Development of controlled Nd:YAG laser for medical applications

Several medical fields are concerned with applications of thermal lasers such as neodymium-doped, yttrium aluminum garnet (Nd:YAG), argon, and CO2. However, quantification of the necrotic volume of Nd:YAG laser-induced damage is not possible at the time of treatment. Mathematic models and feedback control can help to optimize Nd:YAG laser treatments. We therefore formulated mathematic models for coagulation processes and developed an intelligent Nd:YAG laser system with closed-loop feedback control. Surface temperature evolution proved to be valuable data for real-time control of coagulation and ablation. Infrared thermometry provided the noncontact measurement of temperature. A computer stored the temperature data calculated by the mathematic model. Deviations of surface temperature during the treatment beyond established tolerances causes the Nd:YAG laser system to adjust the laser power automatically.     

Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.     

The laser dressing of resin-bonded CBN wheels by a Q-switched Nd: YAG laser

Resin-bonded cubic boron nitride (CBN) grinding wheels are widely used in industry due to their good grinding ability. There is, therefore, a need to find a good method suitable for the dressing of these wheels. This paper presents a new method dressed by an acoustic-optic Q-switched Nd: YAG laser based on thermal interaction, which is unlike the conventional mechanical dressing methods based on force interaction. The mechanism of the selective removal of the bond was analysed. Experiments of a single pulse ablation on the resin bond and the CBN grains, and the laser dressing of resin-bonded CBN wheels with different dressing parameters have been carried out. The grinding force has been compared for the conventional mechanical dressed wheel and the laser dressed wheel. It is shown that the resin-bonded CBN grinding wheel is suitable for an acoustic-optic Q-switched Nd: YAG laser dressing with radial irradiation, which is better than a continuous wave (CW) laser dressing with radial irradiation and conventional mechanical dressing methods.     

Analysis of pulsed Nd:YAG laser welding of AISI 304 steel

Pulsed laser welding of AISI 304 stainless steel plate was simulated using commercial finite element software to determine the optimal welding conditions. Due to geometric symmetry, only one plate was modeled to reduce the simulation computation time. User subroutines were created to account for a moving three-dimensional heat source and to apply boundary conditions. The material properties such as conductivity, specific heat, and mass density were determined as functions of temperature. The latent heat was considered within the given temperature range. The three-dimensional heat source model for pulsed laser beam butt welding was designed by comparing the finite element analysis results and experimental data. This successful simulation of pulsed Nd:YAG laser welding for AISI 304 stainless steel will prove useful for determining optimal welding conditions.     

应用Nd∶YAG激光加工连杆初始裂解槽

为改善连杆裂解槽加工精度和质量,进而提高裂解连杆的成品率,通过试制两种连杆产品,确定了激光加工参数。采用Nd∶YAG固体激光器对两种类型的连杆进行了裂解槽激光加工试验,分析了采用不同切割参数加工的裂解槽质量,并对激光切割参数进行了优化。结果表明:激光峰值功率、离焦量、切割速度、脉冲频率、辅助气体压力、激光入射角等对裂解槽的加工质量均有很大的影响,其中激光峰值功率2.4kW,脉冲时间0.4ms时,切槽深度为0.453～0.457mm,当脉冲频率与切割速度比值约为3,在非正离焦量状态下,所加工的裂解槽对连杆的裂解非常有利,能够满足M0406连杆的裂解质量要求。     

Fabrication of polycrystalline diamond microtool using a Q-switched Nd:YAG laser

A Q-switched Nd:YAG laser (1,064 nm, 100 ns) was used to machine 2?×?1.5?×?0.5-mm rhombus-shaped tool inserts from a 60?×?0.5-mm circular disk of polycrystalline diamond. A systematic experimental study was undertaken to examine the effects of pulse repetition rate, feed rate, and number of laser passes on kerf, material removal rate, recast layer, surface morphology, and surface roughness. The optimal laser parameters for generating two-dimensional tool profiles were an average power of 3 W, a pulse repetition rate of 2 kHz, a feed rate of 1 mm/s, and a total of 45 laser passes. The beneficial results were a material removal rate of 0.02 mm³/min, kerf width of 27 μm, cutting edge radius of 6 μm, and surface roughness (Ra) of 0.625 μm. Recast layer formation, undulations, and striations were observed in the laser-cut regions. These features were attributed to the presence of a molten layer of cobalt binder, and amorphous carbon and graphite transitioned from diamond. An intriguing feature is the presence of fine particulate matter ranging in size from nanometers to a few micrometers in the laser-cut regions. It is believed that phase transition of diamond and cobalt during laser machining created thermal expansion mismatch stresses sufficient to fracture the solid into fine fragments.     

薄板012Al模具钢脉冲Nd:YAG激光熔凝的研究

采用XRD、TEM和EPMA方法对脉冲Nd:YAG激光熔凝的5Cr4Mo3Si MnVAl(012Al)薄板(厚度为0·8mm)模具钢的相和化学成分变化特征进行了研究。结果表明,脉冲Nd:YAG激光熔凝012Al模具钢前后的相均为α-Fe(M体)和γ-Fe(A体),但衍射峰的位置和残余奥氏体的含量不同,其激光熔凝区既存在颗粒状的Al N杂质、V4C3碳化物、长条状的Mo6C碳化物,又存在板条状马氏体,而其熔化区的合金元素分布基本均匀。     

Microstructural and tribological study of Nd:YAG laser treated titanium plates

In this work, the fretting behaviour of pure Ti plates laser treated with a Nd:YAG pulsed laser was compared to that of untreated Ti plates. Fretting tests were done at room temperature without lubrication. The contact geometry was a cylinder (bearing steel) on a plane. The evolution of both the ratio, μ=Q/P, between the normal and the tangential forces, and the Fouvry's energy criterion (A) were recorded as a function of the number of fretting cycles, N. Energy dispersive spectrometry and micro-Raman spectroscopy were used to analyse the fretting scars. The oxidized layer formed by the laser treatment displayed a mixed slip regime as a function of N, and a smaller fretting coefficient μ than the titanium reference.     

A two-wave 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser

A compact 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser is described. Its parameters are as follows: the wavelength is 1064 nm, the pulse energy is 1.2 J, the pulse duration is 5 ns, the pulse repetition rate is 100 Hz, and the beam divergence is ≤1.6 mrad. The laser light efficiency is 12%, and the full efficiency of the laser system is 4%. Two lasing modes are realized in the laser: at the fundamental frequency and with the frequency conversion into the second harmonic at a wavelength of 532 nm and a pulse energy of 0.3 J.     

Numerical analysis of Nd:YAG pulsed laser polishing CVD self-standing diamond film

Chemical vapor deposited(CVD) diamond film has broad application foreground in high-tech fields.But polycrystalline CVD self-standing diamond thick film has rough surface and non-uniform thickness that adversely affect its extensive applications.Laser polishing is a useful method to smooth self-standing diamond film.At present,attentions have been focused on experimental research on laser polishing,but the revealing of theoretical model and the forecast of polishing process are vacant.The paper presents a finite element model to simulate and analyze the mechanism of laser polishing diamond based on laser thermal conduction theory.The experimental investigation is also carried out on Nd:YAG pulsed laser smoothing diamond thick film.The simulation results have good accordance with the results of experimental results.The temperature and thermal stress fields are investigated at different incidence angles and parameters of Nd:YAG pulsed laser.The pyramidal-like roughness of diamond thick film leads to the non-homogeneous temperature fields.The temperature at the peak of diamond film is much higher than that in the valley,which leads to the smoothing of diamond thick film.The effect of laser parameters on the surface roughness and thickness of graphite transition layer is also carried out.The results show that high power density laser makes the diamond surface rapid heating,evaporation and sublimation after its graphitization.It is also found that the good polish quality of diamond thick film can be obtained by a combination of large incident angle,moderate laser pulsed energy,large repetition rate and moderate laser pulse width.The results obtained here provide the theoretical basis for laser polishing diamond film with high efficiency and high quality.     

小型化单横模单纵模激光二极管泵浦Nd∶YAG激光器

在需要利用光的相干性的场合,如倍频、光参量振荡、全息以及光束的相干合成等对激光器输出的线宽有严格的要求,这时就需要对纵模进行选择。介绍一种小型化单横模单纵模激光二极管泵浦Nd∶YAG激光器,单脉冲能量3.6mJ,重复频率200Hz,脉冲宽度16ns,单横模、单纵模运转。该激光器采用谐振反射器和腔内倾斜标准具对纵模进行选择,试验结果与理论计算比较吻合。该激光器可用作窄脉宽高能激光器的种子源。     

Predictive model and process parameters optimization of Nd:YAG laser micro-turning of ceramics

The present work highlights laser micro-turning operation of 10-mm diameter cylindrical-shaped alumina (Al₂O₃) ceramic using pulsed Nd:YAG laser. The paper also addresses development of mathematical models for correlating the various micro-machining parameters such as laser beam average power, pulse frequency, workpiece rotational speed, assist air pressure, and Y feed rate with the response criteria such as surface roughness and deviation in turned depth for achieving desired surface quality as well as dimensional accuracy during micro-turning operation using Nd:YAG laser system. Response surface methodology-based design of experiments has been adopted for the experimentation. This investigation also highlights the various test results that confirm the validity and correctiveness of the developed mathematical models through analysis of variance test. The test results were analyzed through various response surface plots to study the effect of the process parameters on the aforementioned responses. The results of validation experimentation show a good agreement for the developed empirical models. Sensitivity analyses of the developed models have been done to find out the variation in the output with respect to variations in the significant input process parameters. Moreover, multi-performance optimization has been done to find out the optimal parametric setting for achieving the desired process performances. Analysis also has been made based on scanning electron microscopy micrographs of the laser micro-turned surface achieved during machining at multi-criteria optimization setting.