Evaluation of short pulse and short time thermal transient measurements

Thermal transient recording and the time constant spectrum analysis are widely used methods in the thermal testing and qualification of IC packages. A limitation of these methods is that recording of the complete transient response requires long time. This limitation, however, can be overcome by sophisticated procedures. The first method is to apply short power pulse for excitation; the second one is the interruption of the transients long before the thermal equilibrium is reached. The paper offers algorithms to evaluate these short pulse and short time measurements. The presented methods are suitable if the extraction of the little time constants is needed. This is the case if the transient method is used e.g. for die attach quality checking.     

Broad-band pulse performance of short helices

Helical antennas are popular and well characterized for CW frequency domain performance. Renewed interest in time-domain applications of electromagnetics, such as impulse radar, makes accurate time-domain data on broad-band antennas desirable. Although the principal endfire helix radiation mode has been extensively studied in the frequency domain, other modes important in pulse operation are poorly characterized, making a total Fourier transform approach difficult. We have performed impulse tests on helices with two to five turns, establishing novel features of the response and confirming some aspects of frequency domain data. Quick comparisons to time and frequency-domain modeling codes indicate good correspondence of gross features. Successful octave band-pulse operation was achieved, and a few features of helix pulse response invite further investigation     

短脉冲激光微孔制备的双脉冲方法研究

为了提高纳秒短脉冲激光微孔制备的加工效率,采用了一种新颖的双脉冲方法。通过时域脉冲塑形将调Q激光器产生的普通纳秒脉冲变换为具有几十纳秒脉冲时间间隔的双脉冲序列。使用这种双脉冲序列对不锈钢试件进行打孔实验,与传统单脉冲打孔结果对比发现,在一定条件下双脉冲序列能将打孔烧蚀率提高一个数量级以上。实验中研究了脉冲能量、重复频率以及环境气体压力对双脉冲序列烧蚀率的影响,并将脉冲烧蚀率提高的原因归结为材料预加热、材料溶液的加速以及瞬时准真空环境,对各种机制分别进行了讨论。结果表明,采用双脉冲方法替代普通单脉冲进行金属打孔,可以在相同能量密度,相同脉冲重复频率的情况下大幅度提高脉冲烧蚀率,为高效激光微孔制备提供了新方法。     

Nonlinear response to picosecond pulse excitations inmagneto-dielectric media

Nonlinear responses of magneto-dielectric thin layers to picosecond excitation have been calculated utilizing direct time-domain integration. Relaxations, hysteresis, and magnetic saturation phenomena, associated with the response are discussed in depth. The purpose of the calculation is to provide an analytical method by which physical properties of materials can be identified under picosecond-pulse excitation as well as to explore special cases of excitations in which picosecond pulses are efficiently absorbed. The calculations indicate that by examining the reflected waveform of the incident rectangular picosecond pulse, the amount of magnetic hysteresis and saturation of the material may be estimated. It is shown that magnetic hysteresis will affect the shape of the trailing edge of the reflected signal, whereas the magnetic saturation effect can be identified from the slope of the reflected pulse step. Examples of designs for effective picosecond-pulse screening structures are given     

互注入锁定产生波长可调谐光脉冲的实验研究

本文提出了一种利用两个F -P半导体激光器双向注入锁定产生波长可调谐光脉冲的实验系统。该实验系统只需调节可调谐滤波器就可以方便地选择不同波长的单纵模光脉冲,在2 5nm的波长调谐范围内边模抑制比(SMSR)为2 6dB ,其中18nm的波长范围内高于3 1dB。     

采用短脉冲激光进行微盲孔加工研究

研究激光孔加工的目的 是为了寻找高密度互连印制电路板微盲孔加工的先进工艺.短脉冲激光钻机具有比现有长脉冲激光钻机更高更集中的能量,它们是微盲孔加工技术发展的一个候选者.若采用此类激光钻孔方式,玻璃纤维及树脂等很容易被短脉冲激光去除,也就更有利于微盲孔加工技术提高.     

Transient thermal response of power semiconductors to short powerpulses

Thermal response curves used to calculate the peak junction temperature of power semiconductors are normally derived by experimental identification of the parameters of a known model. Unfortunately the model, developed many years ago, is inappropriate for large surges of short time duration, as they are encountered in present day power conditioning systems. An alternative model is derived, the limits of its accuracy are estimated, and a correction factor is described. A verification of the accuracy of the two methods is also presented. For pulse widths shorter than the thermal transit time, which is in the order of 300 μs, the peak junction temperature can be more accurately calculated with an expression derived in the present work, which takes into consideration the active volume in which the heat is generated, than with the transient thermal response curve. A correction factor, a function of the width of the pulse, inserted in this equation, further improves its accuracy     

光电倍增管对高斯脉冲的响应

本文用脉冲响应函数法分析光电倍增管(PM)对高斯光脉冲的响应,用计算结果解释实验观测的波形及利用公式τp=√τt2-τ02从输出脉宽τt扣除PM引起的增宽τ0,求得输入脉宽τp 的条件及限制。     

太赫兹脉冲的短距离大气传输特性

基于van-Vleck Weisskopf线型与辐射传输色散理论,结合JPL数据库,建立了太赫兹脉冲大气传输衰减与色散模型,形成了对宽频太赫兹辐射脉冲在大气中的吸收衰减的数值模拟能力;并对利用太赫兹时域光谱技术(THzTDS)所获得的透射光谱实测结果进行了对比分析,研究了不同水汽密度对太赫兹时域脉冲幅值、相位及频谱特性的影响.研究结果表明:短距离大气传输条件下,0.1~0.5 THz频段太赫兹脉冲的最大传输速率达20 Gb/s以上,相较于单模光纤,更具短距离通信优势.     

重复频率短脉冲氙灯的特性研究

研究了用作染料激光器泵浦源的短脉冲氙灯,闪光脉宽小于2微秒,光强上升时间小于0.6微秒。在额定负载能量下有效使用寿命大于10~7次。本文主要讨论灯的物理与工艺参数对其负载特性和辐射特性的影响。     

超短脉冲光纤激光器工作原理及其测量

简要阐述了飞秒光纤激光器的基本概念，分析了锁模技术的原理。结合被动锁模光纤激光器的基本构成，描述飞秒脉冲的产生过程。此外，还对飞秒脉冲测量作了介绍。     

基于B-Dot的kA级短脉冲电流测量方法

高压脉冲电流的测量方式主要是Rogowski线圈。B-Dot是一种非侵入式脉冲电流测量探针,但由于B-Dot测量模型的建立以及应用标定等过程与实际应用环境密切相关,且对待测电流强度有严格的要求,目前还未见其在实际kA级短脉冲方面的应用研究。本文在对B-Dot的kA级短脉冲测量方法进行理论研究的基础上,设计了微型B-Dot探针,并利用B-Dot探针对kA级短脉冲电流进行试验。试验结果表明,B-Dot探针适用于kA级脉冲电流的测量,且与理论研究结论一致。     

采用纵模匹配技术的短脉冲注入锁定染料激光器

本文报道了采用纵模匹配技术的短脉冲注入锁定染料激光器系统及实验结果.     

Advanced theory of the photon storage ring leading to the short light pulse generation

We improve the theory of the photon storage ring to evaluate mode locking, and derive pulse modes in the barrel-shaped resonator. We find that the pulse mode is excited when the bunched electron beam is taken into account, and only when the distance between the electron orbit and the mirror surface is close to the resonance values derived earlier. In addition, we numerically examined the characteristics of the pulse modes on the resonator and beam parameters. We also outline the possibility of the femtosecond pulse generation.     

The response of 741 op amps to very short pulses

A 741 op amp behaves like a monostable multivibrator when very short pulses are applied to the noninverting input terminal. It is shown that perturbations on the power supply lines or at the output of the amplifier will directly or indirectly have the same effect on the op amp.     

ZnTe晶体对太赫兹波的电光响应及极化匹配

给出了ZnTe电光晶体折射率和吸收系数随太赫兹波频率而变化的计算曲线,比较了太赫兹波在ZnTe中传播时的相速度和群速度。通过与太赫兹频率和晶体厚度相关的电光效率响应函数,理论计算了ZnTe电光晶体对太赫兹脉冲的探测电光响应,得到了晶体厚度与探测到的太赫兹频谱宽度的定性关系,从计算结果中找到了ZnTe电光晶体在5.3 THz和6.2 THz等多个频点的探测盲点,这些探测盲点来自于ZnTe电光晶体与相应频点太赫兹波的栅格共振吸收。结合自制的大口径太赫兹光导天线和1 kHz脉冲重复频率的太赫兹时域光谱实验系统,通过差分探测技术,从实验上得到了太赫兹波极化方向与〈110〉型ZnTe晶体晶轴方向的六个最佳匹配角度,给出了太赫兹电场最大值随晶轴与太赫兹波极化方向之间夹角变化的曲线及经验公式,这将有利于在实践中对该现象的深入理解和对探测灵敏度的有效提高。     

Calculated and experimental response of thin cylindrical antennas to pulse excitation

We have computed the response of a thin, cylindrical monopole antenna to dc pulse excitation, both in transmission and reception, by use of Fourier transforms and the complex impedance and complex effective height, for pulses of space length ranging from two tenths to twice the monopole length. We have also experimentally determined the reponse and have obtained similar results. We conclude from this comparison that present steady-state antenna theory together with Fourier methods will yield reliable results in calculating the response of cylindrical antennas to dc pulses. We have also made certain other measurements of response to pulses and step functions which are reported herein.     

Damage thresholds at metal surfaces for short pulse IR lasers

Measurements of damage to metal surfaces induced by intense nanosecond pulses of IR radiation are reported. Single-shot damage thresholds of Cu, stainless steel, molybdenum, and aluminum surfaces have been measured for various angles of incidence and the predicted increase in damage thresholds for grazing incidence optical components have been experimentally verified for the first time at 10 μm. In addition multiple-shot damage tests have been performed and practical lifetime curves for Cu mirrors have been established. The results are compared with existing theoretical models and shown to be in general agreement.     

Threshold current characteristics of GaAs lasers under short pulse excitation

Measurements of the temperature dependence of threshold current using both short pulse and CW excitation of GaAs heterostructure lasers with multiquantum well and conventional active layers are presented. Our results show that the carrier density at threshold is weakly temperature-dependent in both types of lasers. This is consistent with the measured carrier lifetime at threshold.