Cr4:YAG被动调Q激光器脉冲波形数值模拟及优化

从Nd:YAG晶体Cr4+:YAG被动调Q激光耦合速率方程组出发,数值求解该方程组,获得了激光脉冲的波形。从能量分布和时间分布的角度分析了被动调Q激光脉冲波形的不对称性。定义了描述脉冲波形的对称因子并分析了其与饱和吸收体初始透过率和输出镜反射率的关系。提出了计算脉冲宽度的新方法,重新计算了在脉冲波形非对称条件下的脉冲宽度及其与饱和吸收体初始透过率和输出镜反射率的关系。提出了优化脉冲波形和脉宽的简便方法。     

Pulse radar reflectometry for fusion plasma diagnostics

A basic principle of pulse radar reflectometry is considered in this paper. A numerical analysis is performed in order to study errors appearing due to the expansion of a microwave pulse reflected from the plasma. A block diagram of the basic pulse radar scheme and its overall performance is presented. The first experimental results obtained on T11-M tokamak are discussed. An improved pulse radar scheme with cross-detection is considered. The results of bench test experiments and future applications of this scheme are discussed.     

Cr4+:YAG被动调Q激光器脉冲波形数值模拟及优化

为了研究被动调Q激光器脉冲的波形对称特性,采用数值求解Nd:YAG晶体Cr4+:YAG被动调Q激光耦合速率方程组的方法,获得了激光脉冲的波形,绘制出了"脉冲对称因子"与饱和吸收体初始透过率和输出镜反射率的关系曲线图;并根据脉冲波形的不对称性,更精确地计算了脉冲宽度,及其与饱和吸收体初始透过率和输出镜反射率的关系.得到参数b=0.6时,脉冲波形对称;b=0.78时,脉宽最小的结论.结果表明,可以通过调整b参数来优化被动调Q脉冲波形对称性和脉宽.     

基于TMS320C64x实现LFM信号的实时脉冲压缩

对脉冲压缩技术的原理进行了研究,并在理论分析的基础上介绍某型雷达信号处理系统基于高速通用数字信号处理器TMS320C64x实现数字脉冲压缩,讨论了几个现实问题。给出了相应的硬件框图、软件流程、算法实现及基于所用硬件进行的专门优化,并给出了仿真波形图。该方法经实际应用证明性能可靠,整体性能符合现场要求。     

激光二极管抽运掺Yb3+光纤放大器获得2.41W超短脉冲输出

对国产掺镱(Yb3 )双包层大模场面积光纤超短脉冲放大器进行了系统的实验研究。以自己搭建的脉冲宽度为2.3ps,重复频率为95MHz的全固态锁模激光器作为种子源,以976nm大功率光纤耦合激光二极管为抽运源,以1.6m国产掺Yb3 双包层大模场面积光纤为增益介质,在11.2W的入纤抽运功率下,将平均功率为100mW的脉冲种子光放大到平均功率2.41W,单脉冲能量达到了25nJ,放大后脉冲的宽度(时域宽度)和光谱都有所展宽。     

Truly balanced pulse generator using microwave transistor and SRD

A novel efficient circuit for Ultra-WideBand (UWB) balanced sub-nanosecond monocycle pulse generation is presented. The pulse generator employs wideband bipolar transistor, step recovery diodes, Schottky diodes, and simple charging and discharging circuitry. Simple transient analysis and design of the circuit are presented along with their operating principle. The pulse generator produces truly balanced monocycle pulse with 500 ps pulse-width and 800 mV peak voltage. The generated monocycle pulse also has very symmetrical positive and negative portions and low ringing level. The presented pulse generator can be used as both a transmitter feeding UWB balanced antennas without broadband baluns and a balanced switching pulse generator that used in UWB receiver.     

激光-等离子体相互作用过程中光子加速的研究

为了研究激光-等离子体相互作用过程中的光子加速(光子频率上移),采用数值模拟方法进行了理论计算和数值计算验证,取得了光子加速的重要计算机模拟结果。结果表明,等离子体激光相互作用过程中的光子频率上移与所用的激光脉冲形式和脉冲宽度有关,存在最佳脉冲宽度和脉冲上升宽度,还存在等离子体电子密度上限。这一结果对进一步研究激光等离子体粒子加速有帮助。     

A Two-Port Magnetoelastic Delay Line in the UHF Region

Results are presented on the investigation of an experimental two-port magnetoelastic delay line using a single crystal rod of yttrium-iron-garnet, over the frequency range of 200 to 1000 MHz. A magnetic bias field is applied parallel to the rod axis. Data is given on delay time and insertion loss as a function of bias field. Both a slow and fast variation of insertion loss with bias field are noted. The slow variation of insertion loss is quite flat and insertion loss is at a minimum, over the range of 900 to 1050 oersteds, for all frequencies from 200 to 1000 MHz. A study of the fast variation of insertion loss shows that this variation occurs only over a portion of the pulse and if the pulse is short enough the fast variation is absent. A study of the effects of small permanent magnets that supply a biasing field orothogonal to the primary biasing field is presented. Insertion loss and pulse distortion are substantially reduced by these magnets.     

超短脉冲激光微孔加工(上)——理论研究

自20世纪60年代激光器被发明以来,其脉冲宽度被不断压缩至亚皮秒及飞秒量级,使得激光加工技术进入到了超短脉冲阶段。为了进一步优化超短脉冲激光的微加工,理论研究必不可少。主要论述了超短脉冲激光与不同类型材料之间的相互作用机制。简述了超短脉冲激光微孔加工中的典型物理特性,如等离子体效应、自聚焦和光丝效应及锥形辐射等。分析了超短脉冲激光微孔加工的理论研究现状,并得出了目前理论研究中存在的问题。     

太赫兹脉冲整形技术研究进展

太赫兹(THz)脉冲整形技术在量子理论、生物医学成像、安全检查、亚毫米波通信等领域都具有重要的学术价值和应用前景。概述了基于飞秒脉冲的整形技术和新型太赫兹辐射材料整形技术,分析了太赫兹脉冲整形器件整形技术目前的研究状况,并对各种整形方法的发展进行了展望。     

反常色散区抽运光子晶体光纤产生的超连续谱

为了研究反常色散区抽运光子晶体光纤产生的超连续谱,采用分步傅里叶方法数值模拟了飞秒激光脉冲在光子晶体光纤反常色散区中的非线性传输和超连续谱产生.结果表明,初始激光脉冲的峰值功率和脉冲初始啁啾对光子晶体光纤反常色散区产生超连续谱形状和带宽是有影响的.这些结论给光子晶体光纤中产生超连续谱提供了参考.     

The influence of the degree of coherence of a semiconductor laser on the statistic of the backscattered intensity in a single-mode optical fiber

The results of the study of the statistical dependence of the backscattered light intensity of a semiconductor laser in a single-mode fiber on the duration of the probing pulse and the source coherence time are presented. It is shown that, for a given light coherence time, the intensity distribution function changes with increasing pulse duration from the function close to the exponential one for the pulse duration approximately equal to the coherence time to the function close to the Gaussian one for the pulse duration exceeding the coherence time. The exponential statistics of scattered light makes it possible to obtain a higher sensitivity for the coherent reflectometer using the direct detection method.     

Fiber optical parametric amplifier pulse source: theory and experiments

An evaluation of a fiber optical parametric amplifier (FOPA)-based pulse source in terms of pulse width and chirp is presented. Experiments are performed when operating the FOPA as a pulse source, requiring a sinusoidally modulated pump. The FOPA is generating pulses at 10 GHz, and are measured using a streak camera capable of measuring pulses as a function of time, wavelength, and intensity. Experimental results are presented together with a theory for chirp and pulse widths that show good agreement.     

Coherent absorption in a homogeneously broadened medium

An investigation of the propagation properties of a short pulse in a resonant absorber with a homogeneously broadened transition is presented with two main questions in mind: 1) the influence of the input pulse area on the transitory regime and on the steady-state propagation; 2) the effects of atomic coherence on the pulse shaping and the time delay of the leading edge of the pulse. The transitory regime of a propagating pulse is investigated and the stability of some asymptotic wave form confirmed. As expected, the transversal relaxation mechanism affects critically the major features of the coherent interaction. A detailed analysis of this problem is also presented.     

激光脉冲对钢材热处理的计算

将激光作用对象视为热物性参数为常量的均匀介质,介绍材料在激光脉冲列作用下温度场的解析计算方法。基于研究结果及钢材马氏体相变模型,提出一种,激光脉冲列对钢材表面相变硬化处理时硬化带尺寸的计算方法,并通过激光热处理实验对计算方法的可行性作出证明。     

Effects of modulation frequency on the structure and electrical characteristics of μc-Si:H films prepared by pulsed VHF-PECVD

Modulation frequency and pulse duty cycle are two key parameters of pulsed VHF-PECVD technology. An experimental study on the mierocrystalline silicon materials prepared by pulsed VHF-PECVD technology in high deposition rate is presented. And combining the diagnosis of plasma process with optical emission spectroscopy （OES）, the dependence of microstructure and electrical properties of thin films on the pulse modulation frequency is discussed in detail.     

Analysis of the performance of a thermal defocusing optical limiterin the transient regime

A theoretical analysis of the performance of a thermal defocusing optical limiter in the transient regime-i.e., when the laser pulse duration is comparable to the acoustic transit time which governs the limiter response-is presented. First, an expression is obtained for the time- and space-dependent refractive index changes induced by a laser pulse in an absorbing liquid. This is used to calculate the nonlinear phase change experienced by the laser pulse while traversing the absorbing medium and then the transmission of the optical limiter. Results on the dependence of the optical limiter's performance on laser pulse duration are presented in a general form and also by considering a specific example     

Dual polarized staggered PRT scheme for weather radars: analysisand applications

Weather radars require long unambiguous ranges, high Nyquist sampling rates and good clutter suppression. In addition, polarization diversity is also used extensively, switching polarization of the transmit pulse on a pulse by pulse basis. This paper presents a dual polarized staggered pulse repetition scheme that can be used for Doppler and polarization diversity measurements in a weather radar. Processing algorithms for radar returns under this scheme are also presented. This pulsing scheme was implemented on the CP-2 radar operated by the National Center for Atmospheric Research. Experimental observations of convective storms using dual polarized staggered pulse repetition scheme in the Colorado front range were made and the results of the data analysis are presented     

半导体激光放大器中超短光脉冲放大过程的研究

本文对超短光脉冲在半导体激光放大器内的放大过程进行理论和实验研究，首次推导出描述这一瞬态变化过程的一系列方程组，并利用方程组进行了数值模拟求解，最后给出与理论相一致的实验结果。     

A conceptual design of a hydrogen-fluoride chemical laser driver for inertial confinement fusion

This paper summarizes the results of a study which assessed the potential of the hydrogen-fluoride (HF) chemical laser as a laser-fusion driver. The evaluation was made by designing a laser system in sufficient detail that potential problems could be identified. A summary of the laser design including amplifier parameters, electron-beam accelerator specifications, gas-handling system, pulse shape considerations, and net efficiency calculations is presented here. The final laser design consists of 20, 100 kJ final amplifiers, which combine to yield a 2 MJ laser output. The energy is delivered in a shaped pulse in which one-half of the energy is delivered in the last 3 ns. The pulse rate is 4 pulses per second and the net efficiency is approximately 3 percent. Consideration is also given to the consequences of varying certain laser parameters. The general conclusion obtained from this study is that the HF laser is an attractive laser candidate for laser-fusion applications.