Effect of energy above laser-induced damage thresholds in the micromachining of silicon by femtosecond pulse laser

A 400 nm second harmonic Ti : sapphire femtosecond laser was applied to structure silicon base on a direct-write process in air. A series of lines were ablated with pulses of 300-fs duration at varying power densities ranging from 50 to 100 nJ of energy on 2″ silicon (1 1 1) wafers. In this event, we investigate and report extensive laser induced thermal damage and redeposition encompassing the ablated lines at high energy levels above the damage threshold of the silicon. In addition, the effect of polarisation on the direction of micromachining is also observed and discussed. The resolution and quality of these lines were also found to hold a linear relationship to the laser energy up to its thermal threshold limit.     

激光辐照热力耦合问题的相似性

 由量纲理论出发,分析了激光辐照热力耦合理论的无量纲化基本方程组。在一定的近似条件下,导出了激光辐照热力耦合问题的一般相似性准则,该相似准则不受与温度相关的材料特性的约束。在此基础上给出了强激光辐照充压圆柱壳体热力效应的缩比方法,并对一组实例进行了计算,得到了缩比模型与原型结果几乎完全相似的结论。理论分析与数值计算表明,激光辐照热力耦合问题在合理的近似下满足相似律。     

激光拉曼光谱内标法测定葡萄糖液浓度

利用葡萄糖溶液的激光拉曼光谱中的特征峰—CCO(1 125 cm-1),以本底溶液水为内标物,组成相对强度,对葡萄糖溶液含量进行了测定研究,其线性范围为0～1.8 mol·L-1,检出限为0.022 7 mol·L-1,共存的KCl和NaCl不引起干扰,用于葡萄糖氯化钠注射液的测定获得了成功。经测定某市售标识量为葡萄糖氯化钠注射液、5%葡萄糖和10%葡萄糖注射液实测平均浓度分别为4.91%,4.93%和9.92%,其回收率分别在71.88%～126.31%,81.02%～124.89%和74.87%～121.32%之间,RSD为5.44%,4.34%和0.94%。该方法具有测定简单、操作方便,无需添加其他任何化学试剂,是一种绿色分析测定方法。     

硫化锌法原子吸收间接测定谷氨酸锌络合物稳定常数

在利用硫化锌法火焰原子吸收间接测定谷氨酸或谷氨酸钠,并对测定机理、络合物组成探讨的基础上,进一步对在最佳测定酸度条件下,所形成的络合物谷氨酸锌的稳定常数,进行了测定和求解获得了成功,在pH 9.0时的碱式谷氨酸锌的稳定常数在3.3×1020～1.4×1021,平均值为β_稳=1.03×1021,其log β_稳=21.013。谷氨酸锌的稳定常数在3.3×1010～1.4×1011,平均值为β_稳=1.03×1011,其log β_稳=11.013。     

硫化锌法原子吸收间接测定半胱氨酸锌络合物稳定常数

利用硫化锌法原子吸收间接测定半胱氨酸时,在最佳测定酸度条件下,所形成的络合物半胱氨酸锌的稳定常数,进行数值测定和理论求解获得了成功：在最佳酸度pH=9.7时的碱式半胱氨酸锌的稳定常数在2.998×1030到3.858×1030之间,平均值为β_稳=3.286×1030,标准偏差为0.315×1030,其logβ_稳=30.517。半胱氨酸锌的稳定常数在7.853×1021到1.011×1022,平均值为β_稳=8.607×1021,标准偏差为0.315×1021,其logβ_稳=21.935。表明原子吸收光谱不仅可用于微量元素的测定和有机化合物的间接测定,也可以进行络合离子的物理形态、物理常数的研究和测定。     

激光诱导击穿光谱定量检测土壤微量重金属元素方法研究

在对激光诱导击穿光谱数据分析的基础上提出了一种可以用于元素定量分析的方法。该方法利用傅里叶分析的方法研究了光谱数据中的不同部分(白噪声、热辐射噪声和原子发射光谱),通过带通滤波实现发射光谱与大部分噪声的分离,得到仅含少量白噪声的发射光谱;通过计算待量化元素谱线与其对应单位强度特征谱线的相似度引入卷积强度来衡量待测谱线的强度。选取Cu 324.75nm作为分析线,Ti 337.28nm谱线作为参考线,采用上述方法对含微量Cu元素土壤样品进行了测量。实验结果显示:Cu元素含量和其卷积强度的线性系数达到0.997 9,计算得到土壤中Cu元素的检测限为44mg.kg-1,达到国家土壤环境质量标准规定的二级土壤中Cu含量要求,测量相对误差在10%以内,表明该方法能够满足土壤微量重金属检测简便、快速的要求。     

Enhancing the adhesive bonding strength of NiTi shape memory alloys by laser gas nitriding and selective etching

Laser gas nitriding process (LGN) was applied on NiTi shape memory alloy to obtain an alloyed surface consisting of TiN dendrites in NiTi matrix. By applying subsequent selective etching process, the matrix material in the alloyed layer can be selectively removed and a three-dimensional network of TiN dendrites is left on the surface protruding from the metal substrate. The 3D dendritic network provides extra surface area and locking mechanism for the adhesion joint. The microstructures of such textured surface were examined. The adhesion jointing characteristics of the surfaces were studied. A 150% increase in the lap-joint strength was achieved in the laser gas nitrided and etched specimen as compared with the sandblasted and etched ones.     

Effect of laser shot peening on precipitation hardened aluminum alloy 6061-T6 using low energy laser

Mechanical properties of engineering material can be improved by introducing compressive residual stress on the material surface and refinement of their microstructure. Variety of mechanical process such as shot peening, water jet peening, ultrasonic peening, laser shot peening were developed in the last decades on this contrast. Among these, lasers shot peening emerged as a novel industrial treatment to improve the crack resistance of turbine blades and the stress corrosion cracking (SCC) of austenic stainless steel in power plants. In this study we successfully performed laser shot peening on precipitation hardened aluminum alloy 6061-T6 with low energy (300 mJ, 1064 nm) Nd:YAG laser using different pulse densities of 22 pulses/mm² and 32 pulses/mm². Residual stress evaluation based on X-ray diffraction sin² ψ method indicates a maximum of 190% percentage increase on surface compressive stress. Depth profile of micro-hardness shows the impact of laser generated shock wave up to 1.2 mm from the surface. Apart from that, the crystalline size and micro-strain on the laser shot peened surfaces have been investigated and compared with the unpeened surface using X-ray diffraction in conjunction with line broadening analysis through the Williamson-Hall plot.     

Determination of adhesive forces in multilayer materials using a laser adhesiometer

A laser adhesiometer is developed to determine the adhesive and cohesive forces in multilayer materials. The obtained experimental dependences are explained using the laser microexplosion model. The advantages of determining the adhesive and cohesive forces using the laser adhesiometer over other methods are grounded.     

Accuracy control of three-dimensional Nd:YAG laser shaping by ablation

Improving the dimensional accuracy along the optical axis without decreasing the materials removing rate is a key issue in three-dimensional laser shaping. This paper presents a concept for performing three-dimensional laser shaping by directly using machining laser as the photo source of the non-contacting measuring device. Due to the high power measuring photo source and a 1.06 μm bandpass filter, the interference caused by the emission light of ablated surface can be effectively avoided, the delay time is not needed to be inserted between the laser pulse and the measurement. So the measurement will not decrease the material removal rate and productivity. By using this system, the shaping accuracy of 30 μm can be achieved at the removing rate of about 4.0×10⁻² mm³/sec for Si₃N₄ ceramic, both are much better than the results obtained before.     

Evaporation of a thin film coated on a substrate induced by a pulsed laser

The two-dimensional Laplace integral transform technique has been applied to get the spatial and temporal temperature distributions in both the molten layer thickness of a thin film coated on a substrate, the still solid part of the thin film of the target and the temperature distribution in the substrate. Also a formula for the time dependence of the evaporated part of the thin film of the target as well as the molten layer thickness of the thin film were obtained. Calculations of the obtained relations were carried out during the irradiation with a pulsed laser. The derivation has taken into account the temperature-dependent absorption coefficient of the irradiated surface and the chemical reaction in the vapor of the thin film. As an illustrative example, computations were carried out on an aluminum thin film coated on a glass substrate.     

Excitation of high energy levels under laser exposure of suspensions of nanoparticles in liquids

Laser exposure of suspensions of nanoparticles in liquids leads to excitation of high energy levels in both liquid and nanoparticle material. The emission spectrum of the colloidal solution under exposure of a suspension metallic nanoparticles in water to radiation of a Nd:YAG laser of a picosecond range of pulse duration is discussed. Excitation of nuclear energy levels and neutron release is experimentally studied on the model system of transmutation of Hg into Au that occurs under exposure of Hg nanodrops suspended in D₂O. The proposed mechanism involves: (i) emission of X-ray photons by Hg nanoparticles upon laser exposure, leading to neutron release from D₂O, (ii) initiation of Hg → Au transmutation by the capture of neutrons. The effect of transmutation is more pronounced using ¹⁹⁶Hg isotope instead of Hg of natural isotope composition. The influence of laser pulse duration on the degree of transmutation (from fs through ns range) is discussed.     

用恒流量热器测定水的比热容

介绍了用恒流量热器测定水的比热容的一种新方法.当达到稳定状态时,电阻丝中电流产生的热量等于流过的水吸收的热量与散逸到环境中的热量之和,利用两次独立的实验消去了散逸到环境中的热量这一未知因素,从而使实验结果的准确度得到显著地提高.     

Effect of laser energy, substrate film thickness and bioink viscosity on viability of endothelial cells printed by Laser-Assisted Bioprinting

Biofabrication of three dimensional tissues by Laser-Assisted Bioprinting (LAB) implies to develop specific strategies for assembling the extracellular matrix (ECM) and cells. Possible strategies consist in (i) printing cells onto or in the depth of ECM layer and/or (ii) printing bioinks containing both cells and ECM-like printable biomaterial. The aim of this article was to evaluate combinatorial effects of laser pulse energy, ECM thickness and viscosity of the bioink on cell viability. A LAB workstation was used to print Ea.hy926 endothelial cells onto a quartz substrate covered with a film of ECM mimicking Matrigel™. Hence, effect of laser energy, Matrigel™ film thickness and bioink viscosity was addressed for different experimental conditions (8-24 μJ, 20-100 μm and 40-110 mPa s, respectively). Cell viability was assessed by live/dead assay performed 24 h post-printing. Results show that increasing the laser energy tends to augment the cell mortality while increasing the thickness of the Matrigel™ film and the viscosity of the bioink support cell viability. Hence, critical printing parameters influencing high cell viability have been related to the cell landing conditions and more specifically to the intensity of the cell impacts occurring at the air-ECM interface and at the ECM-glass interface.     

Characterization of laser ablation plasmas by laser beam deflection

Laser probe beam and multiple-pass deflection techniques were used for real time and in situ monitoring of laser ablation plasma plumes in the mTorr pressure regime. Intensity and transit time of shock wave fronts were studied as functions of focal lens position, laser energy and pressure. The velocity of the shock wave was determined to be up to 30 km s⁻¹ for a pressure of 40 mTorr and to drop below 4 km s⁻¹ at 1 Torr. For transparent targets rear-side shock wave velocity was on to be slower than the corresponding front one. This method promises a reliable diagnostic tool for pulsed laser deposition processing allowing an increase in the quality of coating technologies.     

Determination of wood grain direction from laser light scattering pattern

Laser light scattering patterns from the grains of wood are investigated in detail to gain information about the characteristics of scattering patterns related to the direction of the grains. For this purpose, wood samples of Scots pine (Pinus sylvestris L.) and silver birch (Betula pubescens) were investigated. The orientation and shape of the scattering pattern of laser light in wood was found to correlate well with the direction of grain angles in a three-dimensional domain. The proposed method was also experimentally verified.     

A novel time-integral type laser energy meter based on anisotropic Seebeck effect

We have posed the design of a time-integral type laser energy meter based on anisotropic Seebeck effect for the first time. Anisotropic Seebeck effect is responsible for the laser-induced thermoelectric voltage effect in high temperature superconductor (HTSC) cuprates and colossal magnetoresistance (CMR) manganites thin films grown on tilted single crystal substrates. In this study, for an example, an epitaxial La_2/3Ca_1/3MnO₃ thin film prepared on a tilted LaAlO₃ substrate by standard pulsed-laser deposition (PLD) method is tested with a 1064-nm Q-switched Nd:YAG laser and its 2nd (532 nm), 3rd (355 nm), and 4th (266 nm) harmonics from room temperature to 16 K. The integral of the voltage signal with time shows a good linear relation with the laser energy per pulse in the measured wavelength and temperature range, which confirms the theoretical analysis given in this letter and can be used to design a time-integral type laser energy meter. The sensitivity increases as the film thickness increases or as the thermal diffusion constant decreases, which makes the time-integral type laser energy meter low cost as compared with the peak-voltage type. It operates with fast (nanosecond range) and broad-spectrum (from infrared to ultraviolet) response in wide temperature range (from room temperature to 10s K), and can be useful replacements for pyroelectric power/energy meters.     

原子吸收光谱间接测定碱式胱氨酸锌配合物的稳定常数

利用硫化锌法火焰原子吸收间接测定胱氨酸(Cystine,Cys-Cys)。在碱性条件下,胱氨酸能与硫化锌悬浮液反应生成可溶性碱式胱氨酸锌配位化合物,在pH9·40时达到最大浓度,原子吸收光谱法测定了最大浓度时的配合物含量,并对碱式胱氨酸锌稳定常数进行了测定和理论计算。碱式胱氨酸锌的稳定常数平均值β稳为9·916×1032,其logβ稳=32·996。表明原子吸收光谱不仅可用于微量元素的测定和有机化合物的间接测定,同时也可进行配合离子的物理形态、物理常数的研究和测定。     

Effect of laser energy on the deformation behavior in microscale laser bulge forming

Microscale laser bulge forming is a high strain rate microforming method using high-amplitude shock wave pressure induced by pulsed laser irradiation. The process can serve as a rapidly established and high precision technique to impress microfeatures on thin sheet metals and holds promise of manufacturing complex miniaturized devices. The present paper investigated the forming process using both numerical and experimental methods. The effect of laser energy on microformability of pure copper was discussed in detail. A 3D measuring laser microscope was adopted to measure deformed regions under different laser energy levels. The deformation measurements showed that the experimental and numerical results were in good agreement. With the verified simulation model, the residual stress distribution at different laser energy was predicted and analyzed. The springback was found as a key factor to determine the distribution and magnitude of the compressive residual stress. In addition, the absorbent coating and the surface morphology of the formed samples were observed through the scanning electron microscope. The observation confirmed that the shock forming process was non-thermal attributed to the protection of the absorbent coating.