超声振动系统频率自动跟踪的模糊控制算法研究

针对大功率超声应用中,工作频带窄、频率跟踪速度要求快的特点,提出将模糊控制智能算法（Fuzzy Control）和数字频率直接合成技术（DDS）相结合的频率自动跟踪方案,依据经验归纳制定模糊控制器来快速跟踪工作频率,将驱动频率调节至谐振频率附近;随后只采用DDS进行频率的微调节,使得电源频率工作在超声换能器的谐振频率点上。最后,通过在MATLAB软件中对控制算法进行验证,表明本文算法具有可行性,能够实现对大功率超声波电源的频率自动跟踪。     

CPT原子频标实验研究

介绍了相干布居囚禁（CPT）原子频标的小型、低功耗物理系统,并应用它开展实现了CPT原子频标的激光锁定、微波锁定方案的实验室研究.通过采用电流负反馈将激光频率锁定在原子对激光的吸收峰上,电压负反馈将微波频率锁定在电磁感应透明共振峰上,用该物理系统实现了闭环锁定的实验室桌面CPT频标实验系统.对该实验系统的频率稳定度测量获得200 s内优于5×10^-11τ^-1/2的结果. 关键词： CPT原子频标 频率稳定度 激光稳频     

窄线宽全光纤激光器实现666 W高功率输出

搭建了一台主振荡功率放大（MOPA）结构的窄线宽全光纤激光器。利用噪声相位调制技术将单频激光线宽展宽至0.3 GHz,通过四级放大器结构对10 mW的窄线宽种子激光进行放大,获得了功率为666 W的窄线宽激光输出。该窄线宽激光器输出功率仅受限于泵浦功率,增加泵浦功率有望进一步提高输出功率。     

A system for measuring absolute frequencies of up to 4.25 THz using a Josephson point contact

A system for measuring the absolute frequency of a far-infrared (FIR) laser is described. Josephson point contacts have been utilized in the system as a frequency harmonic mixer connecting microwaves and optically pumped CH₃OH laser lines. The Josephson point contacts are capable of generating beat signals of 90 GHz microwaves and FIR waves of up to 4.25 THz. To measure the frequency of the beat signals from the Josephson junction with a frequency counter, tracking oscillators have been developed, which tracks the beat signals by phase locking and regenerate clean signals for frequency counting. It is shown that the absolute frequency can be measured to an accuracy of about 100 Hz by using the tracking oscillators.     

Research on tunable local laser used in ground-to-satellite coherent laser communication

In order to realize homodyne reception and Doppler frequency shift tracking in ground-to-satellite coherent laser communication, a local laser is experimentally demonstrated in this Letter. It is realized based on modulationsideband injection locking, and has a 10 GHz tuning range, a 1 THz/s tuning rate, a 5 k Hz linewidth, and 16 m W of output power. When applied to a Costas loop in a coherent laser communication system, the local laser can achieve ?5 GHz Doppler frequency shift tracking with a 20 MHz/s frequency shift rate, which is sufficient for the ground-to-satellite coherent laser communication.     

一种无磁化的5 T磁共振射频功率放大器设计

本文介绍了一种可以不接环形器,并在扫描间使用的5 T磁共振射频功率放大器（RFPA）．该RFPA基于驻波高耐受的横向扩散金属氧化物半导体（LDMOS）功率管进行设计,共包含三级放大电路．针对传统磁共振RFPA中带磁芯的传输线变压器进行了无磁化的设计,加强了对反射功率的监控,采用模拟负反馈技术实现了对RFPA非线性的自动矫正．测试结果显示该RFPA的输出功率为2 kW,在负载扰动（反射系数Г<0.5）时,40 dB动态输入范围,其增益线性度≤1 dB,相位线性度≤10°,满足成像需求,验证了该设计方案的合理性与可行性．     

用于Rb原子冷却系统的半导体激光放大(TPA)装置

报道了我们最近研制的780 13m半导体激光放大装置.激光放大管采用Eagleyard公司生产的(EYP-TPA-0780-01000)半导体锥形放大器,当输入的种子源激光功率为25 mW时,放大器输出的激光功率达600mW左右,该光束经过透镜整形,声光调制器频移,然后耦合到单模保偏光纤后,输出功率达110 mW.该激光放大装置可很好的用于高密度冷原子的俘获.     

Alignment locking to suspended Fabry-Perot cavity

In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.     

核磁共振波谱仪用射频功率放大器的设计与实现

介绍了一种应用于核磁共振（Nuclear Magnetic Resonance,NMR）波谱仪的宽频带射频功率放大器的设计与实现,提出了射频功率放大器门控信号的设计,探讨了利用传输线变压器构建功率MOSFET输入输出阻抗匹配网络的方法. 该射频功率放大器采用多级驱动结合功率放大的结构,包含2个工作模块和基于宽频带定向耦合器的辅助电路,支持高带和宽带通道的相关实验. 将该射频功率放大器应用在自主研发的500 MHz高分辨率液体NMR谱仪上,测量射频功放的上升、下降时间及输出线性度,并对比测试¹H和¹³C NMR标样的信噪比,实验结果证明了该设计的可行性.     

Generation of near-Fourier-transform-limited high-energy pulses in a chain of fiber-bulk amplifiers

We demonstrate the generation of high-power near-Fourier-transform-limited pulses with variable pulse duration in the nanosecond regime through a combination of fiber and bulk amplification. The fiber amplifier consists of a dual-stage fiber amplifier based on Nd- and Yb-doped single- and double-clad fibers. The bulk amplifier consists of a four-pass, flash-lamp-pumped Nd:YAG rod. Since no resonance condition is required for locking of the seed source to a slave cavity, the setup is extremely rugged.     

Self-Oscillating Mode of a Nanoresonator

The paper proposes a new graphene resonator circuit which operates on the principle of a self-oscillator and has no drawbacks typical of nanoresonators as mass detectors and associated with their law quality factor, eigenfrequency errors (measurements from resonance curves), and dependence of quench frequency on oscillation frequency (curves with quenching for nonlinear systems). The proposed circuit represents a self-oscillator comprising an amplifier, a graphene resonator, and a positive feedback loop with a graphene oscillation transducer, and its major advantage is in self-tuning to resonance frequency at slowly varying resonator parameters, compared to oscillation periods. The graphene layer with a conducting substrate beneath it forms a capacitor which is recharged by a dc voltage source as its capacitance varies due to graphene deformation, and the recharge current is an oscillation- dependent signal transmitted from the transducer to the amplifier input. The graphene layer is placed in a magnetic field and is deformed when a current from the amplifier output is passed through. By properly choosing the magnetic field direction and the amplifier gain, it is possible to provide swinging oscillation whose amplitude is limited by the amplifier nonlinearity. For the proposed system we present an electromechanical model, dimensionless equations of motion, and numerical data demonstrating the generation of steady-state oscillations with eigenfrequency. Also presented is an analysis showing that the system can have only one limit cycle and that this cycle is always stable. The proposed resonator circuit can be used as a mass detector which determines the added mass from a change in self-oscillation frequency.     

Generation of high-power frequency combs from injection-locked femtosecond amplification cavities

We demonstrate a scalable approach for the generation of high average power femtosecond (fs) pulse trains from Ti:sapphire by optically injection locking a resonant amplification cavity. We generate up to 7 W average power with over 30% optical extraction efficiency in a 68 fs pulse train operating at 95 MHz. This master oscillator power amplifier approach allows independent optimization of the fs laser while enabling efficient amplification to high average powers. The technique also enables coherent synchronization among multiple fs laser sources.     

Scaling of resonance frequency for strong injection-locked lasers

It has been shown that strong optical injection locking can significantly enhance the resonance frequency of semiconductor lasers. In this Letter, we describe the trade-off between the maximum resonance frequency enhancement and the quality factor (Q) of the lossless laser cavity and show that the time-bandwidth product (product of photon lifetime and maximum resonance frequency) is equal to one half the square root of the external power injection ratio. The theoretical model agrees well with our experimental data.     

High-power high beam-quality multi-waveguide CO<Subscript>2</Subscript> amplifiers

The results from modeling the energy characteristics of a multi-waveguide power amplifier are presented. The optical schemes and calculations for the most promising circuits of multichannel waveguide CO₂ amplifiers are given. The amplifying system itself removes the problem of phase locking in individual channels of multichannel systems. The experimental results from the synchronization of arrays of multichannel waveguide CO₂ lasers allow the production of high-power (up to 15 kW) high beam-quality multibeam lasers. Technological lasers with such properties have yet to be produced anywhere in the world.     

Photonic microwave generation and transmission using direct modulation of stably injection-locked semiconductor lasers

Direct modulation of a semiconductor laser subject to stable injection locking is capable of generating microwave subcarriers that are broadly frequency-tunable, more than 4 times its free-running relaxation resonance frequency, and are highly sideband-asymmetric, more than 22 dB. The latter characteristic makes the laser system particularly attractive for radio-over-fiber applications. Therefore, such modulation sideband asymmetry, its underlying mechanism, and its effect on chromatic dispersion-induced microwave power variation are extensively studied, in particular, over a broad range of injection conditions. Mappings showing integrated and global understandings of the modulation sideband asymmetry together with the modulation frequency enhancement are obtained accordingly. Interestingly, it is found that the microwave frequency can be tuned over a broad range while keeping a similar level of modulation sideband asymmetry and vice versa, either of which is achieved by simply changing the injection condition. This, therefore, considerably adds the flexibility and re-configurability to the laser system. The cavity resonance shift due to injection locking is responsible for not only the enhanced modulation frequency but also the modulation sideband asymmetry, where a modification in its previous interpretation is obtained for explanation. The modified modulation characteristics are strong functions of the linewidth enhancement factor, making it possible to choose lasers with proper values of the factor for different photonic microwave characteristics.     

激光调制参数对光纤环型谐振腔光谱特性影响

谐振光学环型腔作为光学陀螺的核心敏感单元,其光学调制谱和与之对应的鉴频曲线的特性成为提高光学陀螺系统检测灵敏度的关键。为了研究光学陀螺的调制和鉴频谱线特性,优化陀螺性能,设计并搭建了实验测试系统,光纤环形谐振腔采用分光比为50∶50、直径17 cm的保偏光纤,总长2.2 m。使用直流高压放大器扫描窄线宽激光器（线宽小于1 kHz）的压电转化模块,扫描频率和电压分别选取20 Hz和1 V,使用模拟比例积分电路进行锁频并反馈给激光器的压电转化模块,使激光器的输出频率跟踪谐振腔实时变化。研究分析了光纤环型谐振腔在两种情况下所对应的透射谱和鉴频曲线:第一种情况为调制电压分别为2 V和4 V,对应调制频率从100 kHz到4 MHz变化;第二种情况为当调制频率为900 kHz,调制电压从2 V到10 V变化。通过实验,得到了不同调制参数下光学陀螺谱线的谐振深度、半高全宽、线性带宽、动态范围、品质因数、标度因数以及对应的锁频精度七种物理量的详细变化情况,并进一步得到了静态测试条件下三种陀螺的最佳调制频率及与之所匹配的调制电压。为进一步研究激光调制对光纤环型谐振腔光谱的影响提供指导。     

贯通导体及其电路对金属腔体内部电磁场的影响

为研究贯通导体及其负载电路对金属腔体内部电磁场的影响,建立了不同贯通导体端接负载模型,使用电磁仿真软件CST进行仿真,利用GTEM室、矢量网络分析仪、功率放大器、ETS电场探头组建实验测试系统,验证了仿真结果的正确性,揭示了贯通导体及其电路对金属腔体内部电磁场的影响规律。研究结果表明:腔体内部电磁场同时受到贯通导体与腔体谐振的影响,在谐振频点干扰场强取得极大值,屏蔽效能取得极小值甚至为负值。贯通导体端接负载不接地与贯通导体两端开路情形相似,贯通导体端接负载直接接地时内部场显著降低,谐振频点降低,贯通导体端接负载浮点接地时内部场变化规律低频时与开路模型相似,高频时与直接接地模型相似。贯通导体端接负载的电阻值、电容值也会影响腔体的内部场。     

X-band dielectric Cerenkov maser amplifier experiment

An X-band dielectric Cerenkov maser amplifier experiment is reported. The amplifier system consisted of a solid, thermionically generated electron beam propagating through a cylindrical waveguide partially filled with an annular, dielectric liner. The input signal was provided by a tunable (9-10.3 GHz) magnetron with power up to 10 kW. Electron beam voltages and currents of up to 250 kV and 100 A could be generated for 1 μs pulse durations. The system was configured to operate in the TM₀₁ mode of the dielectric-lined waveguide. In this experiment the gain of the system with respect to the length of the dielectric liner was studied at a fixed input frequency of 10.3 GHz. At electron beam parameters of 160 kV and 60 A, a power gain of 24 dB over 56 cm of interaction length was measured for an input power of 4.5 kW, corresponding to a maximum RF amplified power of 1.15 MW and 12% efficiency     

High-efficiency, single-stage 7-kHz high-average-power ultrafast laser system

We demonstrate a simple and practical single-stage ultrafast laser amplifier system that operates at a repetition frequency from 1 to 10 kHz, with millijoule pulse energy and as much as 13 W of average power. The repetition rate can be adjusted continuously from 1 to 10 kHz by new all-solid-state pump laser technology. This is to our knowledge the highest average power ever obtained from a single-stage ultrafast laser amplifier system. This laser will significantly increase the average power and the repetition rate that is easily accessible for high-field experiments such as coherent x-ray generation or for laser-synchrotron studies.     

Effects of Small Signal Injection on Laser Diode Pumped Hybrid Bistable System with Large Delay

Effects of small signal injection on an electro-optical bistable system with a very large delay are theoretically and experimentally investigated from the viewpoint of linear stability analysis. The resonance phenomena and frequency locking are observed when sinusoidal and rectangular small signals are additively injected into the system. Experiments confirm that theoretical results obtained by linear stability analysis are good predictions of the effects of both resonance and frequency-locking phenomena and show the dependence of these phenomena on the system parameters. As an application of the frequency locking phenomenon to the dynamical memory, the phase identification of the memory oscillation using the frame pulse externally injected is successfully executed.