Improving thermal efficiency and stability of laser welding process for magnesium alloy by combining power modulation and subatmospheric pressure environment

The laser welding(LW)process of highly reflective materials presents low thermal efficiency and poor stability.To solve the problem,the effects of subatmospheric environment on LW process,technological parameters in subatmospheric environment on weld formation and welding with sinusoidal modulation of laser power on the stability of LW process in subatmospheric environment were explored.The AZ31magnesium(Mg)alloy was used as the test materials.The test result revealed that the weld penetration in subatmospheric environment can increase by more than ten times compared with that under normal pressure.After the keyhole depth greatly rises,significantly periodic local bulge is observed on the backwall surface of the keyhole and the position of the bulge shifts along the direction of the keyhole depth.Eventually,the hump-shaped surface morphology of the welded seam is formed;moreover,the weld width in local zones in the lower part of the welded seam remarkably grows.During LW in subatmospheric environment,the weld penetration can be further greatly increased through power modulation.Besides,power modulation can inhibit the occurrence of bulges in local zones on the backwall of the keyhole during LW in subatmospheric environment,thus further curbing the significant growth of the weld widths of hump-shaped welding beads and local zones in the lower part of welded seams.Finally,the mechanism of synchronously improving the thermal efficiency and stability of LW process of highly reflective materials through power modulation in subatmospheric environment was illustrated.This was conducted according to theoretical analysis of recoil pressure and observation results of dynamic behaviors of laser induced plasma clouds and keyholes in the molten pool through high speed photography.

Review of high-power pulsed systems at the Institute of High Current Electronics

In this paper,we give a review of some most powerful pulsed systems developed at the Institute of High Current Electronics(HCEI),Siberian Branch,Russian Academy of Sciences,and describe latest achievements of the teams dealing with these installations.Besides the presented high-power systems,HCEI performs numerous investigations using much less powerful generators.For instance,last year much attention was paying to the research and development of the intense low-energy(<200 kV)high-current electron and ion beam and plasma sources,and their application in the technology[1-3].

Effect of Hot Carrier on Amplitude Modulation and Demodulation of Gaussian High Power Helicon Wave in Homogeneous Longitudinally Magnetized Strain Dependent Dielectric Material

In the present communication, the hydrodynamic model is used to investigate the amplitude modulation as well as demodulation of an electromagnetic wave of high power helicon pump wave into another helicon wave in strain dependent dielectric material incorporating carrier heating (CH) effects. The consideration of CH in modulation and demodulation is prime importance for the adding of new dimension in analysis of amplification of acoustic helicon wave. By using the dispersion relation, threshold pump electric filed and growth rate of unstable mode from the modulation and demodulation of the high power helicon wave well above from the threshold value will be discussed in the present analysis. The numerical analysis is applied to a strain dependent dielectric material, BaTiO3 at room temperature and irradiated with high power helicon wave of frequency 1.78 × 1014 Hz. This material is very sensitive to the pump intensities, therefore during studies, Gaussian shape of the helicon pump wave is considered during the propagation in stain dependent dielectric material and opto-acoustic wave in the form of Gaussian profile (ω0,κ0) is induced longitudinally along the crystallographic plane of BaTiO3. Its variation is caused by the available magnetic field (ωc), interaction length (z) and pulsed duration of interaction (τ). From the analysis of numerical results, the incorporation of CH effect can effectively modify the magnitude of modulation or demodulation of the amplitude of high power helicon laser wave through diffusion process. Not only the amplitude modulation and demodulation of the wave, the diffusion of the CH effectively modifies the growth rate of unstable mode of frequency in BaTiO3. The propagation of the threshold electric field shows the sinusoidal or complete Gaussian profile, whereas this profile is found to be completely lost in growth of unstable mode. It has also been seen that the growth rate is observed to be of the order of 108 - 1010 s-1 but from diffusion of carrier heating, and that its order is enhanced from 1010 - 1012 s-1 with the variation of the magnetized frequency from 1 to 2.5 × 1014 Hz.

Energy measurement system of a large-aperture high power laser experiment platform

An energy measurement system in a large-aperture high power laser experiment platform is introduced. The entire measurement system includes five calorimeters, which carry out the energy measurement of the fundamental frequency before the frequency conversion unit, remaining fundamental frequency, remaining second-harmonics, third-harmonics,as well as the energy balance measurement after the frequency conversion unit. Combinational indirect calibration and direct calibration are employed to calibrate the sampling coefficients of the calorimeters. The analysis of the data showed that, regarding the energy balance coefficients, combinational calibration approach gives a higher precision, and leads to an energy balance with 1%; and regarding the energy sampling coefficients for the various wavelengths after the frequency conversion, the results from direct and combinational calibration are consistent. The uncertainties for all energy sampling coefficients are within 3%, which guarantees the reliability of the energy measurement for the laser facility.

Challenges of high power diode-pumped lasers for fusion energy

This paper reviews the different challenges that are encountered in the delivery of high power lasers as drivers for fusion energy.We will focus on diode-pumped solid-state lasers and we will highlight some of the main recent achievements when using ytterbium,cryogenic cooling and ceramic gain media.Apart from some existing fusion facilities and some military applications of diode-pumped solid-state lasers,we will show that diode-pumped solid-state lasers are scalable to inertial fusion energy(IFE)'s facility level and that the all-fiber laser scheme is very promising.

High-energy and high-peak-power GHz burst-mode all-fiber laser with a uniform envelope and tunable intra-burst pulses

We report a Yb-doped all-fiber laser system generating burst-mode pulses with high energy and high peak power at a GHz intra-burst repetition rate.To acquire the uniform burst envelope,a double-pre-compensation structure with an arbitrary waveform laser diode driver and an acoustic optical modulator is utilized for the first time.The synchronous pumping is utilized for the system to reduce the burst repetition rate to 100 Hz and suppress the amplified spontaneous emission effect.By adjusting the gain of every stage,uniform envelopes with different output energies can be easily obtained.The intra-burst repetition rate can be tuned from 0.5 to 10 GHz actively modulated by an electro-optic modulator.Optimized by timing control of eight channels of analog signal and amplified by seven stages of Yb-doped fiber amplifier,the pulse energy achieves 13.3 mJ at 0.5 ns intra-burst pulse duration,and the maximum peak power reaches approximately3.6 MW at 48 ps intra-burst pulse duration.To the best of our knowledge,for reported burst-mode all-fiber lasers,this is a record for output energy and peak power with nanosecond-level burst duration,and the widest tuning range of the intra-burst repetition rate.In particular,this flexibly tunable burst-mode laser system can be directly applied to generate high-power frequency-tunable microwaves.

An evaluation of sustainability and societal impact of high-power laser and fusion technologies:a case for a new European research infrastructure

Fusion energy research is delivering impressive new results emerging from different infrastructures and industrial devices evolving rapidly from ideas to proof-of-principle demonstration and aiming at the conceptual design of reactors for the production of electricity.A major milestone has recently been announced in laser fusion by the Lawrence Livermore National Laboratory and is giving new thrust to laser-fusion energy research worldwide.Here we discuss how these circumstances strongly suggest the need for a European intermediate-energy facility dedicated to the physics and technology of laser-fusion ignition,the physics of fusion materials and advanced technologies for high-repetitionrate,high-average-power broadband lasers.We believe that the participation of the broader scientific community and the increased engagement of industry,in partnership with research and academic institutions,make most timely the construction of this infrastructure of extreme scientific attractiveness.

Researching the 915 nm high-power and high-brightness semiconductor laser single chip coupling module

Based on the high-speed development of the fiber laser in recent years, the development of researching 915 nm semiconductor laser as main pumping sources of the fiber laser is at a high speed. Because the beam quality of the laser diode is very poor, the 915 nm laser diode is generally based on optical fiber coupling module to output the laser. Using the beam-shaping and fiber-coupling technology to improve the quality of output beam light, we present a kind of high-power and high-brightness semiconductor laser module, which can output 13.22 W through the optical fiber. Based on 915 nm GaAs semiconductor laser diode which has output power of 13.91 W, we describe a thoroughly detailed procedure for reshaping the beam output from the semiconductor laser diode and coupling the beam into the optical fiber of which the core diameter is 105 μm and the numerical aperture is 0.18. We get 13.22 W from the output fiber of the module at 14.5 A, the coupling efficiency of the whole module is 95.03% and the brightness is 1.5 MW/cm2-str. The output power of the single chip semiconductor laser module achieves the advanced level in the domestic use.

定向能武器在电磁空间的运用

为探讨以激光武器和高功率微波武器为代表的定向能武器在电磁空间中的作战应用,采用演绎和类比的研究方法,从电磁频谱的物理原理和战争基本规律出发,论述电磁空间的基本性质、电磁火力的基本特点、电磁精确战的基本原理,以及定向能武器的基本定位、优势劣势、软硬杀伤。分析定向能武器在电磁空间的信息破坏力与信息创造力,梳理总结定向能武器的主要作战场景及运用方式,最后就加快定向能武器走向实战提出建议。

基于微通道散热的板条激光放大器热仿真分析

众所周知,热效应是限制大功率高能量激光器发展的一大瓶颈,在高能激光产生的过程中伴随着大量的废热产生,影响高能量激光器的光束质量甚至会影响其正常工作。为了保证高能量激光器的稳定运作并研究其工作物质的散热过程中的热分布状态,本文建立了一种用于高能Zig Zag板条激光放大器的双端入水微通道散热模型,利用CFD模拟仿真软件在额定工况下对微通道与空腔热沉进行散热对比,还研究了模型的可变参量:通道高度、翅片厚度,以及水流量对于散热性能的影响。模拟研究发现本文提出的微通道热沉冷却效果优于全腔水冷效果,微通道热沉将晶体表面最高温差控制在4℃以内,表面温度也降低了32;同时在压降允许范围内优化通道参数能再将冷却效果提升10,实现增益介质分布式高效散热。

大功率高能脉冲激光电源设计

根据YAG激光器对大功率高能量脉冲电源的应用需求,设计了一种大功率脉冲激光电源,可实现高脉冲能量重复频率输出及充电电压灵活调控。前级充电网络采用串联LC谐振变换器,后级脉冲形成网络选择晶闸管触发LC放电电路。最终,研制了1台7 kW实验样机,最大重复频率10 Hz,最高充电电压2.2 kV,可实现单脉冲最高700 J电能输出,满足大功率高能脉冲输出的应用需求,实验测试结果验证了设计的可行性。

电压源型风电比例影响区域电网频率调整研究

随着新能源大比例接入新型电力系统中,区域电网的频率稳定性问题凸显。为了研究风电在区域电网中对新能源系统稳定运行能力的影响,针对电压源型风电占比对区域电网频率调整的影响开展研究。对风电频率需求相应特性和电压源型风电机组控制进行分析,提出了在电压源型风电机组不同占比结构下的区域电网新能源场站容量分配评估方法。在Matlab/Simulink中对不同电压源型风电占比下的电网频率响应特性进行验证。结果表明,随着在混合风电场内配置一定比例的电压源型风电机组,可以有效地改善区域电网的频率稳定性。

高功率激光器光束质量测量的衰减缩束仿真研究

光束质量因子M^(2)是表征高功率激光器横模特性的主要参数,针对目前光束质量分析仪只能用于小口径、低功率激光器光束质量评估的问题,开展了高功率激光器光束质量测量的衰减缩束技术原理与仿真研究。建立了衰减缩束组件的仿真模型,利用有限元的方法对光学元件在高功率激光下的热致像差进行研究,得出热致像差的峰谷(PV)值小于82 nm时,对光束质量因子的影响小于5%。当光束通过衰减组件时,如果发生退偏,光束质量因子将偏小。基于泽尼克多项式和光束质量因子计算模型,研究分析了缩束组件波前畸变对测量的影响,并通过Zemax仿真分析看出,在装调时入射光与缩束组件中心光轴夹角视场小于7°时,对光束质量因子测量的影响小于5%。

Simulation study of broadband long-pulsed amplification in high-power laser systems

Accurately and efficiently predicting the fundamental-frequency temporal shape of broadband long-pulsed lasers is very important in research on the properties of high-power laser amplifiers. In this study, we first propose that analytic electric polarization in the temporal domain is applied to broadband long-pulsed pulse amplification. We first verify the accuracy of this algorithm in the dozens of picoseconds range and the results are consistent with Miro software. Then we simulate the broadband long-pulsed amplification. The simulation results indicate that the front edge of the output pulse is more enlarged than the end edge owing to saturation and that the gain narrowing induces severe amplitude modulation. Analytic electric polarization in the temporal domain is effec- tive and precise for investigating the broadband pulse amplification in the time scale from dozens of picoseconds to nanoseconds, and the computation time can be decreased by at least 4 orders of magnitude.

Analysis on FM-to-AM conversion of SSD beam induced by etalon effect in a high-power laser system

FM-to-AM(frequency modulation-to-amplitude modulation)conversion caused by nonuniform spectral transmission of broadband beam is harmful to high-power laser facility.Smoothing by spectral dispersion(SSD)beam is a special broadband beam for its monochromatic feature at the given time and space on the near field.The traditional method which uses the optical spectral transfer function as filters cannot accurately describe its AM characteristics.This paper presents the theoretical analysis of the etalon effect for SSD beam.With a low-order approximation,the analytic model of the temporal shape of SSD beam is obtained for the first time,which gives the detailed AM characteristics at local and integral aspects,such as the variation of ripples width and amplitude in general situation.We also analyze the FM-to-AM conversion on the focal plane;in the focusing process,the lens simply acts as an integrator to smooth the AM of SSD beam.Because AM control is necessary for the near field to avoid optics damage and for the far field to ensure an optimal interaction of laser-target,our investigations could provide some important phenomena and rules for pulse shape control.

EMP control and characterization on high-power laser systems

Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.

Evolution of low-frequency noise passing through a spatial filter in a high power laser system

The theoretical model of spatial noise passing through a spatial filter is established in high power laser system under the small signal approximation. The transmission characteristic for a noise signal passing through spatial filters with different magnifications is analyzed by numerical simulation, according to the actual structure of the high power laser system. The results show that the spatial modulation period of low-frequency noise getting through the pinhole will be proportional to the magnification of the spatial filter. When the magnification is less than 1, the safe low-frequency noise will be extruded into the high-frequency region, which is the fast increasing part, and finally develops into the most dangerous part which can damage the optical devices. The conclusion of this research improves the relay imaging theory of a spatial filter and provides an important theoretical basis for a general design of high power laser systems.

高效供电系统可靠性与安全性分析

高效供电系统主要用于满足严苛环境下的工作特性和稳定性要求,但由于锂离子电池内部是非稳态的电化学体系,因热滥用、电滥用和机械滥用等异常情况发生可能会产生安全隐患,从而造成严重经济损失和恶劣社会影响。文章提出一种分析验证该系统可靠性与安全性的方法,通过建模分析、热设计仿真验证其可靠性;且经热设计仿真分析满足在高温下长循环情况下的温度稳定性,但水冷板仍有优化空间;采用硬件分析法,分析该系统锂离子电池储能模块在使用过程中可能或实际发生的故障模式,为提高系统使用可靠性、运行安全性等提供依据。

机载定向能武器发展趋势及关键技术研究

为应对机载定向能武器对空战的影响,需科学研判其发展状态。首先研究了机载定向能武器的基本概念、作战应用场景、优缺点,分析了国外主要机载高能激光、高功率微波武器发展概况,然后对国外在定向能武器发展方面的主要做法进行研究。国外通过前瞻布局、建立完善管理机构、持续投入、重视配套试验设施建设等方式快速推进机载定向能武器的发展,而机载高能激光武器将是最先实现装备的定向能武器,机载高功率微波武器在短期内的主要形式仍是作为导弹、炸弹的战斗部。机载定向能武器应尽早开展装机试验,持续攻克小型化、高功重比、高效环控、电磁兼容防护等难题,突破作战使用方式、总体设计集成、试验平台构建、试验评估等关键技术,并持续投入、长远布局协同发展、重视通用空中试验平台的建设,加大探索性飞行试验,通过不断的试验促进技术的逐步成熟。

高能量密度低功耗一体化机器人动力轮模组技术研究

针对传统自动引导车(AGV)和自主移动机器人(AMR)传动链存在的低能量密度、高能耗、大尺寸等问题,提出了一种集成电机、减速机、抱闸和编码器的一体化机器人动力轮模组设计。该设计采用大中空电机内嵌减速机的一体化设计技术,显著减少了传动链占用的空间,从而提升了AGV/AMR的底盘空间利用率和整车性能。与传统设计方案相比,该动力轮模组实现了12%的能量密度提升和23%的效率增加,有效降低了功耗损失,为AGV/AMR的传动链设计提供了一种高效、紧凑的解决方案。