基于窄脉冲传输的脉冲展宽IGBT驱动电路

设计了一种采用高压隔离脉冲变压器传输窄脉冲,然后应用脉冲展宽电路实现宽脉冲驱动信号输出的无源IGBT驱动电路。采用正电压turn-on窄脉冲和负电压turn-off窄脉冲组合传输的方式以减小高压隔离脉冲变压器的体积和重量,脉冲展宽电路使IGBT在turn-on脉冲上升沿导通,在turn-off脉冲上升沿关断,且其具备储能功能,无需高压隔离辅助直流电源为其供电。脉冲信号发生电路和过流保护电路耦合设计,使IGBT在正常关断和过流保护关断情况下,其栅极都处于反压偏置状态,以提高IGBT关断的快速性和可靠性。将驱动电路用于级联Marx高压电路中IGBT开关的驱动,turn-on脉冲和turn-off脉冲的脉宽均选择为2 μs,结果表明,Marx电路在输出脉冲电压峰值为20 kV时工作稳定,且脉宽在3.5~50 μs之间连续可调,等离子体负载下的输出电压和电流波形显示,打火情况发生时,过流保护电路工作稳定可靠。该驱动电路可有效实现宽脉冲驱动信号的产生,具有较强的可靠性和实用性。     

Intermediate Self-similar Solutions of the Nonlinear Schrödinger Equation with an Arbitrary Longitudinal Gain Profile

We study pulse propagation in a normal-dispersion optical fibre amplifier with an arbitrary longitudinal gain profile by self-similarity techniques. We show the functional form of the development of low-amplitude wings on the parabolic pulse, which are associated with the evolution of an arbitrary input pulse to the asymptotic parabolic pulse solution. It is found that for the increasing gain the amplifier output corresponding to the input Gaussian pulse converges to the asymptotic parabolic pulse solution more quickly than the output obtained with the input hyperbolic secant pulse, whereas for the decreasing gain the input pulse profiles have nearly no effect on the speed of convergence to the parabolic pulse solution. These theoretical results are confirmed by numerical simulations.     

Optimal control of multiphoton ionization processes in aligned I2 molecules with time-dependent polarization pulses

Multiphoton ionization processes in aligned I2 molecules are actively controlled by the homemade pulse shaping system, with which a time-dependent polarization pulse can be generated and controlled. We find a correlation between a femtosecond time-dependent polarization pulse and the production efficiency of evenly or oddly charged molecular ions. We achieve much better controllability of the correlation with a time-dependent polarization pulse than with a pulse having a fixed ellipticity. The results suggest the existence of an unknown tunnel ionization mechanism which is characteristic of a time-dependent polarization pulse. Our experiments point to new directions in optimal control studies with molecular systems, as discussed in the text.     

Generation of time-dependent ultra-short optical pulse trains in the presence of self-steepening effect

Starting from the extended nonlinear Schr?dinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time related ultra-short optical pulse trains in an optical fibre are numerically simulated by adopting the split-step Fourier algorithm. The results show that the self-steepening effect can cause the characteristic of the pulse trains to vary with time, which is different from the self-steepening-free case where the generated pulse trains consist of single pulses which are identical in width, intensity, and interval, namely when pulses move a certain distance, they turn into the pulse trains within a certain time range. Moreover, each single pulse may split into several sub-pulses. And as time goes on, the number of the sub-pulses will decrease gradually and the pulse width and the pulse intensity will change too. With the increase of the self-steepening parameter, the distance needed to generate time-dependent pulse trains will shorten. In addition, for a large self-steepening parameter and at the distance where more sub-pulses appear, the corresponding frequency spectra of pulse trains are also wider.     

Time delay reduction in low power ultrashort pulse and pulse stream propagation with overlapping soliton pair

Propagation of temporal 50 femtosecond pulse and pulse stream, which is realized by substituting each input pulse with reduced-order overlapping soliton pair, is investigated through short standard single-mode fiber. For the pulse stream the initial inter-pulse delay is selected to be 227 fs and the pulses are to be perturbed to avoid collision with the neighboring pulses. This method reduces the pulse time delay and properly retains the amplitude despite tradeoff between these two. This is a significant improvement in the low power femtosecond pulse and pulse stream propagation.     

激光在烟幕中传输的蒙特卡罗模拟

建立蒙特卡罗计算模型,模拟计算1.06μm脉冲激光在石墨烟幕中的传输.分析透过率与石墨粒子粒径、烟幕浓度、烟幕厚度的关系,用卷积方法计算一定宽度的脉冲激光穿过烟幕后的波形,数值仿真δ脉冲和矩形脉冲激光在各种石墨烟幕中的时间展宽特性.模拟结果表明:石墨粒子存在一最佳半径(0.16μm),该半径的石墨粒子烟幕不仅使激光能量衰减最强,而且产生的时间展宽也最显著;激光脉冲宽度越小,其波形变化和时间展宽越显著,微秒量级脉宽的激光脉冲穿过烟幕后波形变化和时间展宽效应不明显.     

脉冲形状对脉冲经光纤放大器传输后功率增益的影响

基于描述脉冲放大过程的时间相关非线性辐射迁移方程,对不同形状脉冲经掺镱光纤放大器传输后的功率特性进行了分析,该方程同时考虑了光与介质的相互作用.数值结果表明,在相同的脉冲能量下,不同形状脉冲经放大器放大后的功率增益随入射脉冲形状不同而不同,并且功率增益的差异在脉冲前沿比较大.这使得放大器输出脉冲峰值向前沿的偏移量以及峰值功率的放大倍数都与脉冲形状有关.尤其是当入射脉冲的能量较大时,不同形状脉冲的峰值功率的放大倍数明显不同,以超高斯脉冲为最大,高斯脉冲、双曲正割脉冲次之,洛伦兹脉冲最小.     

半导体器件HPM损伤脉宽效应机理分析

 HPM能量在半导体器件损伤缺陷区的热量沉积以及向周围材料的热量扩散,是造成半导体器件损伤脉宽效应的机理;分别得到了全脉宽段、长脉宽段和短脉宽段的损伤经验公式,该损伤经验公式能较好地对实验和理论模拟效应数据进行拟合。     

负载配置对进入射频管热丝脉冲能量的影响

大功率高压脉冲变压器次级双绕组灯丝馈电时，两绕组平衡不良及负载不对称配置可能引起脉冲能量严重进入射频管热丝，影响进入热丝脉冲能量的因素有负载配置方式，两绕组平衡程度，脉冲宽度及幅度，平衡电容的大小，等效灯丝阻抗及脉冲变压器本身的有关参数等，其中主要因素为负载配置方式。定量分析表明：负载对称配置具有明显的优越性；     

强损耗介质中相干光脉冲的传输效应

本文利用密度矩阵形式的Bloch方程和Maxwell方程耦合,讨论了相干光脉冲在共振强损耗介质中的传输过程,同时考查了脉冲演化和对介质的影响,得到了脉冲面积的阶跃式下降和空间损耗粒子数的周期振荡等强损耗条件下特有的瞬态相干现象。 关键词：     

一种重复频率的-功率脉冲发生器

介绍了一种由 Ｔｅｓｌａ 变压器和同轴脉冲形成线组成的高功率、高重复频率的脉冲发生器,其特点是结构紧凑,容易实现小型化。简述了该发生器的结构,论述了基本原理和特性,分析了应用前景。     

一种重复频率的高功率脉冲发生器

 介绍了一种由Tesla变压器和同轴脉冲形成线组成的高功率、高重复频率的脉冲发生器，其特点是结构紧凑，容易实现小型化。简述了该发生器的结构，论述了基本原理和特性，分析了应用前景。     

在反常色散区艾里脉冲与光孤子相互作用规律的研究

本文采用分步傅里叶法,研究了在反常色散区孤子和艾里脉冲相互作用的规律,并且对相互作用后的孤子和艾里脉冲各自的强度、时域和时移进行了MATLAB仿真.通过仿真发现光孤子和艾里脉冲在光纤中相互重叠时,交叉相位调制(XPM)就会建立并且这种调制会影响孤子和艾里脉冲的性质.在相互作用过程中,孤子的形状保持不变,但是受到艾里脉冲自加速特性的影响孤子会发生偏移.艾里脉冲受XPM的影响会转化为孤子,传播方向也会发生偏移.可见,XPM使得艾里脉冲和孤子各自的性质都相互影响着对方.艾里脉冲和孤子的时域也会受到XPM的影响,使得原本不相同的脉冲形状都转变为含有一个主峰和一个次峰的相似结构,并且主峰和次峰的位置和脉冲宽度也大致相同,这也是艾里脉冲能够转换为孤子的一个依据.另外本文还模拟了不同输入强度r下的孤子和艾里脉冲的变化情况,模拟发现不管是艾里脉冲还是孤子时移都随着输入强度r的增大而增大,并且它们的变化趋势都是一样的,同时模拟还发现在相同的的r值下,时移也会随着a值的增大而增大.     

五阶非线性光纤中连续谱相位扰动下的光传输与脉冲串产生

根据包含五阶非线性的扩展非线性薛定谔方程,数值研究了高斯型连续谱相位扰动而不是传统单色扰动下基于调制不稳定性的高重复率脉冲串产生.结果表明:脉冲串也能像传统情形那样形成,但却呈现出不同的特性.如脉冲数目有限,且各脉冲的高度、强度及间距不等.脉冲数目随传输距离增加而增加.而五阶非线性能使脉冲宽度和间距变小因而有利于高重复率脉冲串产生,负五阶非线性则相反.对脉冲串形成过程中演变啁啾的数值计算表明,啁啾及其随距离的变化都是高度非单调的,五阶非线性将改变啁啾的范围和量值.     

不同波形脉冲激光的时域误差对相干合成的影响

相干合成技术是实现高功率、高亮度光纤激光系统的重要技术途径.然而, 脉冲激光阵列中常常存在时域误差,这将影响脉冲激光的相干合成效果. 建立了脉冲激光存在时域误差时的相干合成理论模型,并在不同波形(方波、三角波、正弦波) 的脉冲激光存在时域误差时,对相干合成光束在远场的脉冲波形、峰值功率、 光强分布和桶中功率(PIB)等特性进行了数值计算和对比分析.计算结果表明: 方波脉冲激光相干合成光束的脉冲波形受时域误差影响严重,光强分布和PIB随着时域误差 的增大发生线性变化;三角波脉冲激光相干合成光束的脉冲波形和峰值功率受时域误差 影响严重,光强分布和PIB在时域误差较大时随着时域误差的增大发生较为剧烈的变化; 正弦波脉冲激光相干合成光束具有较好的输出特性,在两路正弦波脉冲激光相干合成中, 将两脉冲之间的时延控制在脉冲持续时间的10%以内,就能取得良好的合成效果.     

Transient response analysis of photoconductive detector under ultra-short laser pulse radiation

The transient response characteristics of HgCdTe photoconductive detector under the radiation of ultra-short laser pulse have been discussed in detail. Specifically, the transient effect of pulse width to the temperature of electronics and crystal lattice, and corresponding resistance changes of detector are mainly discussed. Based on traditional drift-diffusion model, considering that the temperature of electronics and crystal lattice are different under the ultra-short laser pulse, the double-temperature equation is joined to describe the semiconductor carriers’ dynamics features. Using the numerical method, the transient response characteristics of detector in the case of ultra-short pulse have been worked out. The calculation results show that: When the pulse width is greater than nanosecond pulse, the temperature of electronics will be equal to which of crystal lattice. If the pulse width is less than nanosecond pulse, the temperature of electronics is higher than which of the latter. After the end of a pulse, the rebound resistance of detector will be higher than the dark resistance because of the thermal effect. The heat effect is more obvious when a pulse with narrower width and higher energy density incident to the detector.     

Experimental investigation and numerical simulation of the spatio-temporal dynamics of nanosecond pulses in Q-switched Nd:YAG lasers

This paper reports on an experimental investigation and numerical simulation of the spatio-temporal dynamics of the pulse formation in flashlamp-pumped Q-switched Nd:YAG lasers. The temporal evolution of the spatial intensity distribution is measured with a fast two-dimensional CCD camera. The measurements are performed for two lasers with different cavity configurations. A laser with an optically stable resonator and an internal mode aperture generated pulses with a spatial intensity distribution which is Gaussian at all times during the 10-ns-long pulse. During the pulse evolution the value of the beam-quality factor M²remains below 1.3. In a laser with a positive-branch unstable resonator the laser pulse also starts with a Gaussian intensity distribution, but becomes rapidly non-Gaussian. The corresponding M²values increase from about 1 at the beginning of the formation of the pulse to more than 12 in the tail of the pulse. The measurements are compared with the results of a numerical simulation which takes the laser amplification, the properties of the laser cavity, and the diffraction of the beam in the laser cavity into account. The spatio-temporal dynamics of the pulse formation predicted by the numerical model are in good agreement with the experimental results.PACS 42.60.Jf     

Threshold and conversion experiments on seeded stimulated Raman scattering

High energy-conversion efficiencies in Stimulated Raman Scattering (SRS) are demonstrated both in experiments and by simulations for pump powers below SRS threshold. The scattering is induced by a short seed pulse at the Stokes frequency, the pulse width of which is much shorter than the pump pulse width and which is comparable with the medium's dephasing time.     

Optimum conditions for superradiant damping

The conditions are investigated under which cooperative or superradiant effects are greatest in an inhomogeneously broadened atomic system that is excited by a coherent light pulse. The coupled non-linear atomic equations of motion are solved numerically for excitation pulses of various areas. It is shown that the absolute intensity of the response decreases strongly with decreasing pulse are below π, but that the relative superradiant contribution increases with decreasing pulse area. The reasons for this are discussed, and it is suggested that excitation by a pulse in the neighborhood of π/2 may represent an optimum compromise for the observation of superradiance.     

双色场驱动不对称分子气体产生平台区超连续光谱

研究了双色场驱动下不对称分子气体产生的高次谐波. 通过计算机数值模拟,发现当波长为800 nm,脉宽为10 fs的基频场和波长为1200 nm的控制场组成的多光周期双色场作用于不对称分子时,不对称分子的高次谐波在平台区的末端呈现出超连续结构. 超连续谱谱宽达80 eV,可以支持傅里叶极限脉宽为50 as的脉冲输出. 传播后,超连续谱变得更平滑,而且,直接选取超连续谱上的一段,可以得到脉宽约为90 as的单个脉冲输出. 关键词： 超连续谱 阿秒脉冲