Efficient multi-keV X-ray sources from Ti-doped aerogel targets

We have measured the production of hnu approximately 4.7 keV x rays from low-density Ti-doped aerogel (rho approximately 3 mg/cc) targets at the OMEGA laser facility (University of Rochester), with the goal of maximizing x-ray output. Forty OMEGA beams (lambda(L)=0.351 microm) illuminated the two cylindrical faces of the target with a total power that ranged from 7 to 14 TW. The laser fully ionizes the target (n(e)/n(crit)相似文献   

Theoretical study of Pr3+:ZBLAN upconversion ultraviolet fiber laser based on 4f5d state

A theoretical study of the kinetics of two-step-excitation upconversion ultraviolet cw fiber laser based on the 4f5d state in Pr3+:ZBLAN is performed using steady population rate equations and light propagation equations. Under different Pr3+ concentrations, the dependence of the threshold pump powers on the other pump power, the variations of laser output power with reflectivity of output coupler, pump powers and fiber length as well as the dependence of the optimum fiber length on pump powers are investigated.The results predict some optimum laser parameters for maximizing output power.     

Maximum peak power generation from Q-switched lasers

We investigate the optimization of Q-switched lasers based on maximizing the laser peak power and apply the Lagrange multiplier technique to obtain the numerical solutions of the output mirror reflectivity and several key laser parameters such as the peak power and output energy. Meanwhile, according to the optimization theory described in our paper, a Nd:YAG Q-switched laser is studied experimentally and the results showed this theory is very useful in high gain-to-loss ratio laser design tradeoffs.     

Optimization of the peak power of doubly Q-switched lasers with both an acousto-optic modulator and a GaAs saturable absorber

The key parameters of an optimally coupled doubly Q-switched laser are determined by maximizing the peak power. A group of general curves are generated by considering the single-photon absorption (SPA) and two-photon absorption (TPA) processes in the GaAs, along with the Gaussian spatial distributions of the intracavity photon density, the initial population-inversion density and the influence of the acousto-optic (AO) Q-switch. These results are compared with the results obtained when maximizing the output energy of the doubly Q-switched laser, and the differences between these approaches are discussed. Sample calculations for a laser-diode-pumped Nd³⁺:YVO₄ laser with both an AO modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.     

High-energy handling capabilities of optical fibers: Application to pulse compression and direct generation of megawatt picosecond pulses

The compression of the output of a Q-switched, mode-locked Nd:YAG (130 ps, 1.06 m) is reported for a number of different core-size single mode, multimode and polarization preserving fibers at power levels near the damage threshold. In maximizing the energy throughput, the main limitations are dielectric breakdown and nonlinear induced birefringence. Compressed pulse stability is found to depend critically on core size at this power level. An optimized compressor has been obtained capable of compression factors up to 35 (3.7 ps) with peak power in excess of 2 MW. Second-harmonic generation has been observed in polarization preserving fibers.     

无源标签反向散射调制性能的分析和测试

分析了无源超高频射频识别系统阅读器接收机获得最大有效吸收功率的标签侧条件,讨论阻抗失配对标签反向散射链路调制系数的影响,导出阅读器接收机归一化有效吸收功率、解调输出信号的信噪比下边界和接收端误码率三者的反向散射调制系数表达式.在开阔的室内环境下,完成了不同参数条件下的反向散射调制系数测试.测试研究表明,反向散射调制系数位于区间 时,标签可以被正确识别. 关键词： 射频识别 无源标签 反向散射调制 调制系数     

Enhanced vibration energy harvesting using dual-mass systems

A type of dual-mass vibration energy harvester, where two masses are connected in series with the energy transducer and spring, is proposed and analyzed in this paper. The dual-mass vibration energy harvester is proved to be able to harvest more energy than the traditional single degree-of-freedom (dof) one when subjected to harmonic force or base displacement excitations. The optimal parameters for maximizing the power output in both the traditional and the new configurations are discussed in analytical form while taking the parasitic mechanical damping of the system into account. Consistent of the previous literature, we find that the optimal condition for maximum power output of the single dof vibration energy harvester is when the excitation frequency equals to the natural frequency of the mechanical system and the electrical damping due to the energy harvesting circuit is the same as the mechanical damping. However, the optimal conditions are quite different for the dual-mass vibration energy harvester. It is found that two local optimums exist, where the optimal excitation frequency and electrical damping are analytically obtained. The local maximum power of the dual-mass vibration energy harvester is larger than the global maximum power of single dof one. Moreover, at certain frequency range between the two natural frequencies of the dual-mass system, the harvesting power always increases with the electrical damping ratio. This suggests that we can obtain higher energy harvesting rate using dual-mass harvester. The sensitivity of the power to parameters, such as mass ratio and tuning ratio, is also investigated.     

Improving InGaN-LED performance by optimizing the patterned sapphire substrate shape

The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates(PSSes) with different values of fill factor(f) and slanted angle(θ) are investigated in detail.The threading dislocation(TD) density is lower in the film grown on the PSS with a smaller fill factor,resulting in a higher internal quantum efficiency(IQE).Also the ability of the LED to withstand the electrostatic discharge(ESD) increases as the fill factor decreases.The illumination output power of the LED is affected by both θ and f.It is found that the illumination output power of the LED grown on the PSS with a lower production of tan θ and f is higher than that with a higher production of tan θ and f.     

充中性气体相对论返波振荡器的粒子模拟研究

用PIC粒子模拟方法研究了充中性气体相对论返波管的物理机制,成功模拟了电子束碰撞充入返波管中的中性气体电离产生等离子体的过程,在电子束传输的路径上形成离子通道,有效中和电子束径向空间电荷力,有利于电子束的传输及束波相互作用产生微波。增加中性气体密度,返波管的输出频率明显上移,其辐射的功率和效率比相同的真空器件也有明显的提高。     

System analysis of dual purpose cycle for desalinated water and power production

A comprehensive study of the characteristics of a solar powered dual purpose plant for simultaneous production of fresh water and electric power was carried out. The dual purpose (hybrid) cycle consisted of an open water cycle and a Freon-12 closed power cycle interlinked in the heater and condenser of the power cycle. The hybrid system operating conditions and criteria for adjusting the ratio of fresh water production to power generation was described and their effects on the total system were evaluated.The results indicated an increase of both desalinated water and output work with the increase of hot water pressure and temperature. The increase of maximum pressure in the power cycle decreases the amount of desalination and increases the output work up to a certain limit. The inlet water temperature has no effect on the rate of fresh water production, but its increase results in a decrease in the output work. The system study showed the advantages of the proposed cycle as compared to other single purpose plants for desalination or power generation.     

充中性气体相对论返波振荡器的粒子模拟研究

 用PIC粒子模拟方法研究了充中性气体相对论返波管的物理机制，成功模拟了电子束碰撞充入返波管中的中性气体电离产生等离子体的过程，在电子束传输的路径上形成离子通道，有效中和电子束径向空间电荷力，有利于电子束的传输及束波相互作用产生微波。增加中性气体密度，返波管的输出频率明显上移，其辐射的功率和效率比相同的真空器件也有明显的提高。     

He-Ne激光器旁侧光谱强度与激光输出功率的关系

理论分析和实验结果都证明：He-Ne激光器的旁侧光谱强度与激光输出功率有着密切的关系．对于3S2能级，有激光输出的粒子数少于无激光输出的粒子数，而对于2P4能级，有激光输出的粒子数多于无激光输出的粒子数．对于3S2和2P4能级都有如下关系：有无激光输出的粒子数差随激光输出功率单调变化，前单调上升，后单调下降；当激光输出功率增大到一定值时，粒子数差变化很小。     

Joint Deep Reinforcement Learning and Unsupervised Learning for Channel Selection and Power Control in D2D Networks

Device-to-device (D2D) technology enables direct communication between devices, which can effectively solve the problem of insufficient spectrum resources in 5G communication technology. Since the channels are shared among multiple D2D user pairs, it may lead to serious interference between D2D user pairs. In order to reduce interference, effectively increase network capacity, and improve wireless spectrum utilization, this paper proposed a distributed resource allocation algorithm with the joint of a deep Q network (DQN) and an unsupervised learning network. Firstly, a DQN algorithm was constructed to solve the channel allocation in the dynamic and unknown environment in a distributed manner. Then, a deep power control neural network with the unsupervised learning strategy was constructed to output an optimized channel power control scheme to maximize the spectrum transmit sum-rate through the corresponding constraint processing. As opposed to traditional centralized approaches that require the collection of instantaneous global network information, the algorithm proposed in this paper used each transmitter as a learning agent to make channel selection and power control through a small amount of state information collected locally. The simulation results showed that the proposed algorithm was more effective in increasing the convergence speed and maximizing the transmit sum-rate than other traditional centralized and distributed algorithms.     

Optimum array design to maximize Fisher information for bearing estimation

Source bearing estimation is a common application of linear sensor arrays. The Cramer-Rao bound (CRB) sets a lower bound on the achievable mean square error (MSE) of any unbiased bearing estimate. In the spatially white noise case, the CRB is minimized by placing half of the sensors at each end of the array. However, many realistic ocean environments have a mixture of both white noise and spatially correlated noise. In shallow water environments, the correlated ambient noise can be modeled as cylindrically isotropic. This research designs a fixed aperture linear array to maximize the bearing Fisher information (FI) under these noise conditions. The FI is the inverse of the CRB, so maximizing the FI minimizes the CRB. The elements of the optimum array are located closer to the array ends than uniform spacing, but are not as extreme as in the white noise case. The optimum array results from a trade off between maximizing the array bearing sensitivity and minimizing output noise power variation over the bearing. Depending on the source bearing, the resulting improvement in MSE performance of the optimized array over a uniform array is equivalent to a gain of 2-5 dB in input signal-to-noise ratio.     

欠匹配型磁绝缘感应电压叠加器次级阻抗优化方法

磁绝缘感应电压叠加器(MIVA)次级阻抗对脉冲功率驱动源和负载之间的功率耦合具有重要影响.基于稳态磁绝缘Creedon层流理论和鞘层电子流再俘获(re-trapping)理论,建立了负载欠匹配型MIVA电路分析方法,数值分析获得了MIVA输出参数(输出电压、阴/阳极电流和电功率)随负载欠匹配程度的变化规律.考虑阴极传导电流作为闪光X射线照相二极管的有效电流,建立了以MIVA末端X射线剂量率最大为目标的次级阻抗优化方法.获得了欠匹配型MIVA次级优化阻抗Z_(op)~*的变化规律:随着X射线剂量率对电压依赖程度提高,欠匹配型MIVA次级优化阻抗Z_(op)~*呈指数降低;负载阻抗越大,Z_(op)~*越大.     

Extremal harmonic active control of power for a monocylinder hybrid powertrain

This article presents a real-life application for the extremal harmonic active control of power [1] applied on a hybrid engine setup. The active control was adapted for a hybrid powertrain constituted of a one-cylinder diesel engine coupled with a permanent magnet synchronous machine. The problem was formulated in the harmonic domain and the control objective was to extremalize energetic criterions. Three criterions were considered: minimizing the speed ripple of the engine, maximizing the mechanical reactive power (mechanical impedance adaptation) and maximizing the active electric power for energy harvesting. The results show that, for the first and second orders of the ripple, speed oscillations can be completely cancelled and reactive power and active power can be optimized on-line. The implicit extremal controller converged rapidly, remaining stable even when the mean engine speed changed abruptly. These results confirm the robustness and the applicability of the extremal harmonic active control for industrial applications.     

甲醇--动力联产系统热功转换过程分析

在联产系统能量和物质转换过程模拟和分析的基础上,重点研究了热功转换过程及其与甲醇合成过程的相互影响.得到部分联产率对系统输出功、甲醇合成压缩机耗功、甲醇产量、合成塔副产蒸汽的影响.并对比了动力独立生产系统和部分联产系统供电效率.     

Theoretical study of power amplification in tapered fiber with multi-seed parallel injection

We proposed the concept of parallel injection power amplification.A tapered fiber amplifier with multi-seed sources by the way of parallel injection was studied.The lower-order modes are excited and more than 90%of the input signal power remains in the fiber core if optimal injection and taper design are set.The power in the doped-core is amplified with high optical-optical efficiency.When light is propagating along the fiber,the higher-order modes are filtered which results in the high output beam quality.Incoherent combination of multi-seed lights launched through the wide end gives rise to the output power of several kW.     

5 MW中性束弧电源DC/DC变换器的设计与实现

中性束离子源弧放电具有气体放电等离子体的非线性特性,工作时还会受到气体压强、外磁场、阴极状态等因素的影响,采用晶闸管相控调压技术的弧电源很难实现对这种大功率电弧的稳定的闭环控制。为此,提出了一种多相多重的大电流DC/DC变换器,具有响应速度快、电流上升时间短、电流纹波小等特点,大幅提高了离子源弧放电闭环控制的稳定性。设计了滤波电感能量回馈电路,弧电源可以根据中性束系统的需要使弧电流快速减小0%~100%(可调),然后根据控制信号迅速恢复正常弧电流输出,形成一个弧电流凹坑。电源还采用超级电容储能技术,使电源体积减小了2/3,电网容量小于10 kVA。离子源放电时不会受到电网波动的影响,弧放电更加稳定。实验数据显示：该电源最大输出为220 kW/1500 A,电流纹波在1%以内,电流上升时间约100 s,最大超调量小于3%,可以满足5 MW中性束离子源及系统的要求。     

High-repetition-rate femtosecond optical parametric chirped-pulse amplifier in the mid-infrared

We discuss a dual-stage optical parametric chirped-pulse amplifier generating sub-100-fs pulses in the mid-infrared at a repetition rate of 100 kHz. The system is based on a 1064 nm pump laser and a 3–4 μm difference frequency generation seed source derived from the output of a femtosecond fiber laser amplifier. Both lasers are commercially available, are diode-pumped, compact, and allow for turn-key operation. Here, we focus our discussion on the design and dimensioning of the optical parametric chirped-pulse amplifier. In particular, we review the available gain materials for mid-infrared generation and analyze the impact of different stretching scenarios. Timing jitter plays an important role in short-pulse parametric amplifier systems and is therefore studied in detail. The geometry of the amplifier stages is optimized through a full 3-dimensional simulation with the aim of maximizing gain bandwidth and output power. The optimized system yields output pulse energies exceeding 1 μJ and an overall gain larger than 50 dB. The high repetition rate of the pump laser results in an unprecedented average power from a femtosecond parametric system at mid-infrared wavelengths. First experimental results confirm the design and the predictions of our theoretical model.