Multi-pulsed white light sintering of printed Cu nanoinks

Pulse management of white light to maximize the sintering efficiency of a rapid (msec) and substrate-protective method, intense pulsed light (IPL), was studied systematically with a printable Cu nanoink. An excessive pulse energy that induces deleterious defects on the Cu film along with damage on a plastic substrate was dissipated into multiple sub-pulses while maintaining a total energy budget over the threshold level for successful Cu sintering. Electrical properties of the metal layers were analyzed in conjunction with pulse formation factors such as average energy, pulse duration, peak power and pulse number to determine their respective effects on IPL sintering. In the quantitative results, the optimized sintering conditions of copper nanoparticles with a mean diameter of 30 nm and a fixed total irradiated pulse energy of 32 J cm(-2) were a pulse number and pulse width of > 4 and < 3 msec, respectively.     

NIST-NPL interlaboratory pulse measurement comparison

A comparison of the pulse parameter values obtained from the pulse measurement services of the National Institute of Standards and Technology, USA, and the National Physical Laboratory, U.K., was performed. The comparison was based on the pulse parameters of amplitude, transition duration, overshoot, and undershoot (preshoot). The parameter comparison was applied to raw (measured) waveforms, corrected waveforms (if applicable), and reconstructed waveforms. The results of the comparison show that the pulse parameter values for both national laboratories are within published uncertainties.     

A low-cost bipolar pulse generator for high-frequency ultrasound applications

A design of a low-cost bipolar pulse generator for high-frequency (HF) ultrasound applications is presented. The pulse generator can produce N cycle (1-255 cycles) bipolar pulses with center frequency over 60 MHz. The measured pulse amplitude was over 160 Vpp, and the pulse ringing was less than 0.3 Vpp (i.e., signal-to-ring ratio is 55 dB). The pulser can be used in high-frequency ultrasound Doppler and B-mode imaging applications with arrays.     

截断式脉冲水射流冲蚀煤岩特性数值模拟

基于光滑粒子动力学和有限元法(smoothed particle hydrodynamics-finite element method,SPH-FEM)耦合算法,建立了截断式脉冲水射流冲蚀煤岩的数值计算模型。通过对比数值模拟结果与相同工况下的实验结果,验证了该模型的有效性。在此基础上,探究了在截断式脉冲水射流冲击作用下,煤岩沿射流轴向的损伤演化过程,分析了煤岩围压、脉冲长度、脉冲间距及射流速度对煤岩冲蚀深度及速度的影响规律。结果表明:煤岩的冲蚀深度随着围压增大而减小;随着脉冲长度的增加,煤岩的冲蚀深度逐渐减小,冲蚀速度经历了先增大后减小的过程;脉冲间距对冲蚀深度的影响较小,煤岩的冲蚀速度随脉冲间距的增大呈现出线性减小的变化趋势;脉冲速度对冲蚀深度及速度影响较为显著,且随着脉冲速度的增加,冲蚀深度及速度整体呈增长趋势。     

Evaluation of laser drilling of holes in thermal barrier coated superalloys

Abstract

Laser drilling of precise holes in thermal barrier coated Ni based superalloys has been studied. The interplay between various hole geometrical features such as hole shape, taper, barrelling, undercut, etc. and laser parameters such as pulse energy, pulse width and pulse repetition rate have been examined. The hole diameters are seen to follow a linear dependence on the incoming laser power densities for pulse width up to 2·0 ms. However, such a linear dependence was not observed for a pulse width of 3·0 ms. It was found that high pulse energy and short pulse width (high power density) gave crack free recast layer, whereas low pulse energy and longer pulse width (low power density) gave microcracks in the heat affected layer of superalloy. The significant barrelling observed in IN718 material at low power density values is due to multiple reflection of the incident beam from the cavity in combination with plasma formation at the evaporation front and trapping of the incident radiation causing excessive heating in that region.     

High rate deposition of insulating TiO2 and conducting ITO films for optical and display applications

An innovative reactive pulse magnetron sputtering (PMS-) system allowing to change the pulse mode (unipolar, bipolar or pulse packet) and the pulse parameters (duty cycle, frequency) of the discharge has been used to deposit different materials at high deposition rates. The new pulse packet mode combines the two fundamental pulse modes of unipolar and bipolar by applying ‘packets’ of unidirectional pulses between the two targets and changing the polarity of the discharge after each packet. As a new pulse parameter, the number of pulses of each packet can be varied. The advantages of the PMS-system were demonstrated by the reactive deposition of insulating titanium oxide (TiO₂) and conducting indium tin oxide (ITO) films. The TiO₂ layers sputtered on unheated substrates at deposition rates of up to 50 nm*m/min exhibited amorphous, mixed anatase/rutile or rutile structure in dependence of the pulse mode and the pulse parameters that were applied. Hardness, Young's modulus, roughness and refractive index varied in dependence of the structure of the layers. Although the sputtering from ceramic target is the most common coating technique for ITO, another economical way is the use of metallic InSn-targets. The effect of various pulse modes on the optical and electrical properties of reactively sputtered ITO layers on float glass was investigated. The specific resistivity of ITO was minimized by process parameter optimisation.     

Dissimilar welding of carbon steel to 5754 aluminum alloy by Nd:YAG pulsed laser

Laser welding of low carbon steel to 5754 aluminum alloy was studied in keyhole welding mode in steel-on-aluminum overlap configuration. In order to decrease formation of intermetallic components during laser welding, effect of laser power, pulse duration and overlapping factor was investigated. Tensile test was performed to identify the effect of each parameter on the weld. The phase composition was characterized by energy dispersive spectrometry and Vickers microhardness test and microstructure by optical and scanning electronic microscopes. Results obtained show that increasing peak power (in constant pulse energy), pulse duration (in constant peak power) and overlapping factor (in constant pulse energy and peak power) will increase percentage of intermetallic components (PIC). On the other hand, decreasing the mentioned parameters will cause destructive effects such as inadequate penetration depth, spattering and cavity formation. Improvement in the tensile strength was attributed to low values of intermetallic components in weld metal. Finally, an optimized peak power, pulse duration and overlapping factor were reported.     

Diode-end-pumped,electro-optically Q-switched Nd:YVO4 slab laser and its second-harmonic generation

We describe the operation of a near-diffraction-limited, 1,064-nm electro-optically Q-switched Nd:YVO4 slab laser that is end pumped by laser-diode stacks and its efficient second-harmonic generation by using a lithium triborate (LBO) crystal. The energy per pulse of 3.6 and 0.8 mJ and pulse widths of 5 and 13.5 ns were obtained at repetition of 5 and 40 kHz, respectively. With a LBO crystal, a maximum output power of 15.6 W at 532 nm was obtained at the repetition rate of 40 kHz, the corresponding conversion efficiency was 60%, and the pulse width was 11.3 ns. At 10 kHz, the pulse energy of 532 nm was 1.2 mJ, and the pulse width was 5 ns.     

Electrochemical determination of pharmaceuticals in spiked water samples

The electrochemical behaviour of acidic and neutral pharmaceutical active compounds (PhACs) was studied by cyclic voltammetry and pulse voltammetric techniques on mercury, carbon nanotube paste, carbon paste and gold electrodes. The best results, in terms of sensitivity, linearity range and detection limits, were obtained by differential pulse voltammetry (DPV) for ofloxacin (LOD 5.2 microM), differential pulse polarography (DPP) for clofibric acid (LOD 4.7 microM) and normal pulse voltammetry (NPV) for diclofenac (LOD 0.8 microM) and propranolol (LOD 0.5 microM). An enrichment step of approximately two orders of magnitude was performed by a solid-phase extraction procedure (SPE) in order to concentrate the samples. The developed method was optimized and tested on spiked river water samples.     

Deposition,structure and hardness of Ti–Cu–N hard films prepared by pulse biased arc ion plating

In this work, Ti–Cu–N hard nanocomposite films were deposited on 304 stainless steel (SS) substrate by using pulse biased arc ion plating system with Ti–Cu alloy target. The effects of negative substrate pulse bias voltages on chemical composition, structure, morphology and mechanical properties were investigated. The composition and structure of these films was found to be dependent on the pulse bias, whereas the pulse biases put little influence on hardness of these films. The XPS spectra of Cu 2p showed that obtained peak values correspond to pure metallic Cu. Cu content in Ti–Cu–N nanocomposite films changed with pulse bias voltage. In addition, X-ray diffraction analysis showed that a pronounced TiN (111) texture is observed under low pulse bias voltage while it changed to TiN (220) orientation under high pulse bias voltage. Surface roughness of the Ti–Cu–N nanocomposite films achieved to the minimum value of 0.11 μm with the negative pulse bias voltage of −600 V. The average grain size of TiN was less than 17 nm. The mechanical properties of Ti–Cu–N hard films investigated by nanoindentation revealed that the hardness was about 22–24 GPa and the hardness enhancement was not obtained.     

Deposition,structure and hardness of Ti–Cu–N hard films prepared by pulse biased arc ion plating

In this work, Ti–Cu–N hard nanocomposite films were deposited on 304 stainless steel (SS) substrate by using pulse biased arc ion plating system with Ti–Cu alloy target. The effects of negative substrate pulse bias voltages on chemical composition, structure, morphology and mechanical properties were investigated. The composition and structure of these films was found to be dependent on the pulse bias, whereas the pulse biases put little influence on hardness of these films. The XPS spectra of Cu 2p showed that obtained peak values correspond to pure metallic Cu. Cu content in Ti–Cu–N nanocomposite films changed with pulse bias voltage. In addition, X-ray diffraction analysis showed that a pronounced TiN (111) texture is observed under low pulse bias voltage while it changed to TiN (220) orientation under high pulse bias voltage. Surface roughness of the Ti–Cu–N nanocomposite films achieved to the minimum value of 0.11 μm with the negative pulse bias voltage of ?600 V. The average grain size of TiN was less than 17 nm. The mechanical properties of Ti–Cu–N hard films investigated by nanoindentation revealed that the hardness was about 22–24 GPa and the hardness enhancement was not obtained.     

Effect of multi pulse current treatment on microstructure and microhardness of resistance spot welded dual phase steel DP590

In this paper, microhardness and microstructural characteristics of dual phase DP590 steel resistance spot weld joint under two different welding conditions (i. e. single pulse and multi pulse) were studied. It was observed that applying multi pulse currents resulted in quasi-equiaxed grains of tempered martensite in fusion zone (FZ) of the weldment. The refinement of microstructure in fusion zone using multi pulse current treatment resulted in reduced hardness of the weld joint.     

Present states and future prospect of fast ignition realization experiment (FIREX) with Gekko and LFEX Lasers at ILE

The fast ignition realization experiment (FIREX) project is progressing. The new short pulse laser system, LFEX laser, has been completely assembled and one of the four beamlets is now in operation. A fast-ignition experiment was performed using this single short pulse combined with the Gekko XII implosion laser. The energy of the GXII implosion laser was about 2 kJ and the pulse width was 1.5 ns. The energy of the LFEX laser was increased upto 800 J and two pulse durations 5 and 1.6 ps were compared. Targets were deuterated plastic shells with gold cones. It was found that the neutron yield was increased by a factor of 30 as a result of the fast electron-induced heating in LFEX 1.6 ps shot. The estimated coupling efficiency between the LFEX laser pulse and the compressed fuel was low (less than 5%). This may be due to pre-plasma formed by light arriving at the target before the main laser pulse. Further investigations and attempts to overcome these problems are now in progress.     

质子交换膜燃料电池不锈钢双极板无氰脉冲镀银

质子交换膜燃料电池不锈钢双极板直流氰化镀银,污染环境、耐蚀性不理想,为此,使用无氰脉冲镀银对不锈钢双极板进行了表面改性。采用XRD,SEM,界面接触电阻测试、模拟燃料电池环境腐蚀等方法,研究了无氰脉冲镀银对不锈钢双极极性能的影响。结果表明：无氰脉冲镀银改善了镀层的微观结构,其接触电阻为镀银处理前的1／10,同时腐蚀电流...     

Experimental study on the design of orifice pulse tube refrigerator

An experimental study on the design of a single-stage orifice pulse tube refrigerator (OPTR) was carried out. It was shown experimentally that there exists an optimum operating frequency which increases with decreasing pulse tube volume. For a fixed pulse tube volume, increasing the pulse tube diameter will improve the performance. The experimental results are used to derive a correlation for the performance of OPTR which correlates the net cooling capacity with the operating conditions and the dimensions of the OPTR.     

Time-resolved beam-quality characterization of copper-vapor lasers with unstable resonators

Beam quality (BQ) of a 4-cm copper-vapor laser (CVL) with unstable resonators of different magnifications was characterized based on time-resolved far-field measurement. It was found that the BQ improvement after each round trip of the cavity cannot be predicted correctly from resonator theory. With a cavity Fresnel number of ~ 300, the achievable CVL BQ at the later part of the pulse was limited to approximately 4 times diffraction limited (×DL), even with a cavity magnification of 130. A pronounced temporal BQ oscillation, which is synchronized with the temporal pulse modulation, was also observed throughout the entire pulse. Examination of the temporal evolution of the far-field spot with use of a gated camera revealed that the strong presence of amplified spontaneous emission (ASE) in the cavity during the entire laser pulse severely limited the achievable BQ because of consecutive cavity feedback that included this highly divergent ASE. BQ deterioration caused by intense ASE throughout the pulse was reduced when a cavity with a smaller Fresnel number was used.     

主动调相型脉管制冷机数值模拟与实验研究

设计了一台主动调相型斯特林脉管制冷机,采用线性压缩机作为脉管制冷机主动调相控制器(APC),连接于冷指热端出口。通过控制调相压缩机与驱动压缩机(PWG)间的位移相位角实现主动调相,从而调节质量流和压力波之间的相位关系,优化制冷性能。利用模拟软件进行数值模拟并进行实验研究。研究结果表明,定输入功下APC与PWG位移相位角为-110°及扫气容积比(PWG扫气容积/APC扫气容积)2.98时,无负载制冷温度最低,同时比卡诺效率最高,能够达到原惯性管型脉管制冷机同样的效率。     

Intracavity second-harmonic generation at 320 nm of an actively Q-switched Pr:LiYF4 laser

We demonstrate pulse laser operation of a Pr:LiYF(4) laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained a maximum laser peak power of 167 W (4 μJ/pulse) with a pulse width of 24 ns at an 11 kHz repetition rate for a 63 nm wavelength. Employing an 8 mm long lithium triborate nonlinear crystal in the laser cavity, we obtained a maximum peak power of 55 W (2.7 μJ/pulse) at 320 nm, which corresponds to a conversion efficiency of 69% with respect to the fundamental laser energy. The UV laser pulse width was 36 ns.     

Materials dynamics under nanosecond pulsed pressure loading

A nanosecond pressure pulse is generated by focusing a nanosecond-pulsed laser onto an aluminum target with plasma confined geometry. A spatially uniform pressure pulse is generated by focusing laser beams with a flat-top spatial energy distribution. High-pressure pulse loading and recovery experiments were performed on yttria-doped (3 mol%) tetragonal zirconia polycrystals at 11 GPa. In the pressure-loaded region, the monoclinic phase was uniformely formed. The transition ratio was approximately 30%. Nanosecond time-resolved Raman spectroscopy was performed on polytetrafluoroethylene under high-pressure pulse loading at 1 GPa, and rapid structural phase transition within 10 ns was revealed.     

Ultrafast optical pulse digitization with unary spectrally encoded cross-phase modulation

A method to digitize the intensity of ultrashort laser pulses for high-speed optical signal processing is described. This digitization was based on the spectral broadening of a weak probe (carrier) pulse by a more intense pump (signal) pulse through the nonlinear optical process of cross-phase modulation (XPM). The signal pulse intensity was varied to generate different spectral widths that can be encoded into digital form. Using a 50-ps time-divided multiplexing pulse train with a waveguide splitter, combiner, and an array of fibers with variable lengths, a unary XPM encoding approach is demonstrated. The spectral encoding scheme can be used to achieve a 5-GHz sampling rate at a 16-level accuracy.