10－6—10－4m2/s黏度液体中靶受力学作用的测试与分析

通过自行研制的光纤传感器对不同黏度液体中材料靶后的力学作用进行研究，获得了液体黏度变化对等离子体烧蚀力、射流冲击力及空泡生存周期的影响. 实验结果表明：液体黏度相同时，靶材所受冲击力幅值随作用激光能量的增加单调上升；液体黏度增加时，靶材所受的冲击力减小，靶材的空化空蚀程度亦减小；受液体黏度增大的影响，空泡膨胀或收缩过程减缓，相应的生存周期也增大. 此外，对空泡溃灭周期公式进行修正, 结果表明修正后的理论估算值与实验值的一致性较好.     

其他应用

TN249 2004064207 激光水下打靶力学效应的测试与分析=Mechanicaleffects during pulsed laser and metals interaction in water[刊,中]/徐荣青(南京理工大学应用物理系.江苏,南京(210094)),陈笑…∥光电子·激光.一2004,15(5).一599-603 采用自行研制的光纤力学传感器研究了在不同能量的脉冲激光作用下水中靶材的力学效应。实验和理论分析研究结果表明,水中靶材依次受到激光烧蚀压力及空泡溃灭产生两次射流冲击力的作用,冲击力幅值随作用激光能量的增加均先上升后下降;而射流产生时刻及空泡溃灭时刻随激光能量增加呈单调递增趋势;且射流产     

环境压强对空泡脉动特性的影响

基于空泡生长和溃灭理论分析不同环境压强对空泡膨胀的最大泡半径、收缩的最小泡半径、膨胀与收缩速度的影响.同时,利用高功率激光与液体物质相互作用产生空泡,采用高速照相机、高频测量水听器实验研究不同环境压强下液体中空泡运动规律,并将实验结果与计算结果进行对比.结果表明:环境压强对空泡脉动特性有较大影响.相同激光能量击穿液体介质时,随着外界环境压强的增加,空泡脉动周期呈现递减趋势;空泡第一次脉动的最大泡半径同脉动周期的变化趋势一致,且数值由快到慢递减;随着外界压强的增加,空泡溃灭的速度越快.随着压强的增大,空泡膨胀与收缩更为剧烈,持续时间更短.     

圆锥边界附近激光空泡溃灭行为的研究

为了研究刚性圆锥边界锥角对激光空泡溃灭行为的影响,文章建立了虚拟平面边界模型, 同时采用阴影摄影术、光偏转法以及数值计算的手段对边界附近空泡溃灭过程进行了研究. 结果表明边界的锥角对空泡的形状、溃灭时间以及液体射流形成均有明显影响. 空泡形状偏离球形的程度和溃灭时间均随锥角的增大而增大,且增大锥角度可以促使射流的形成. 空泡溃灭时间的实验值同理论值具有较高的一致性,验证了虚拟平面边界假设及无量纲距离修正的有效性.     

离子液体[EMIm]Ac比热容、导热系数及黏度的研究

本文通过实验研究,测定在一定温度范围内,离子液体[EMIm]Ac及摩尔分数分别为0.8、0.6、0.4和0.2的[EMIm]Ac水溶液的比热容、导热系数及黏度。实验结果表明:比热容和黏度受温度影响较大,比热容随温度升高而增大;黏度随温度升高而急剧减小;导热系数受温度影响较小;添加水后,随着水含量的增加即水溶液摩尔分数的减小,比热容增大,相比于纯离子液体,比热容最高增加70%;导热系数最高增加35%;其黏度急剧减小,最高减小82%。本文的研究结果为[EMIm]Ac及其水溶液在吸收式制冷方面的应用研究提供了可靠的数据。     

液体流动条件下毛细管管口气泡动力特性实验

通过对液体流动条件下毛细管管口气泡生长及脱离过程进行可视化实验.分析了毛细管管壁浸润性,液体流速以及气体流量对气泡生长脱离过程的影响.实验结果表明:随着液体流速的增大,液体对气泡的横向剪切力增大,气泡的脱离周期减小,气泡的脱离直径也随着减小.同时,实验还发现随着气体流量的增大,使气泡生长动力增大,气泡的脱离周期减小;另外,实验还揭示出毛细管管壁浸润性的改变,将导致气泡生长过程中气固液三相接触线发生径向迁移.     

黏性液体中激光空泡脉动特性的理论和实验研究

通过自行研制的光偏转测试系统对黏性液体中激光空泡脉动特性进行了实验，获得了激光等离子体空泡前两次脉动全过程，从而判定了空泡在脉动过程中对应的最大和最小泡半径；并将不同黏性系数下空泡脉动结果与基于空泡溃灭理论的计算结果进行了对比.结果表明：液体黏性对空泡生存周期、空泡半径，以及泡壁的运动速度等均有影响.受液体黏性影响，空泡膨胀或收缩过程明显变缓，其相应的生存周期也越长.这一研究结果不仅可促进空化研究的深入，也可为合理利用空化现象提供参考. 关键词： 激光泡 脉动特性 黏性 光纤传感器     

固壁面附近激光产生空泡脉动过程的实验研究

采用自行研制的光纤传感器研究了激光等离子体空泡在固壁面附近的脉动特性。实验获得了激光空泡三次膨胀到最大位置对应的波形图;并据此判定了激光空泡在脉动过程中对应的最大泡半径和溃灭周期;在此基础上结合空泡溃灭理论,计算了激光泡溃灭周期的延长因子κ。结果表明:随着脉动次数的增加,最大泡半径依次减小;随着作用激光能量的增大,最大泡半径,空泡溃灭周期的延长因子κ均增大;而无量纲参量的增大将导致延长因子的减小。所得到的延长因子同样可用于无限域流场。     

用于瞬态力学量测试的光学传感器设计及应用

基于光纤耦合反射式光束偏转法,提出了一种可用于瞬态力学量测试的光学传感器,并详细给出了该测试机理.采用该传感器,在靶材对心处实时检测到由于空泡在固体靶材附近溃灭时射流冲击力引起的靶材瞬态微小变形.通过对该传感器定标可以进一步得到作用冲击力大小.这种传感器的应用将有助于了解激光诱导产生空泡射流运动特性及其对靶材的损伤机制.     

上浮气泡在壁面处的弹跳特性研究

本文针对毫米量级的上浮气泡在壁面处的弹跳现象进行数值研究.基于势流方法求解气泡的运动,同时考虑气泡的表面张力作用.在伯努利方程中,对气泡与壁面之间水膜中因黏性引起的压力梯度进行修正,开发相应的计算程序,计算值与实验值符合良好.从气泡弹跳的基本现象入手,研究了特征参数对气泡弹跳过程的动态特性以及最终平衡形态的影响.发现随着泡在撞击壁面之前上浮距离增大,气泡回弹距离和弹跳周期增加,但是当上浮距离增加到一定程度后将不会影响气泡的弹跳特性;表面张力是影响气泡弹跳特性的重要因素,气泡的弹跳周期随其增大逐渐减小,但回弹距离却呈现先增后减的规律;最后,影响气泡最终平衡形态的主要因素是气泡的浮力参数与韦伯数.     

The absorption of ethylene in the 10-μm region

The ν₇, ν₁₀, and ν₄ interacting band system has been studied from three complementary sources: classical, diode laser, and waveguide laser spectra. In addition to the two first-order Coriolis interaction terms associated with ζ_7.10^a and ζ_4.10^b, we were obliged to introduce the corresponding second-order terms to obtain a statistical agreement between calculated and experimental data. High-quality vibrational and rotational data are presented for the two infrared active fundamentals, ν₇ and ν₁₀, and the rotational constants for the inactive ν₄ fundamental are determined for the first time. We also present the list of all the infrared transitions starting from the vibrational ground state of ethylene and being in quasi coincidence with CO₂ or N₂O laser lines.     

Optical-to-microwave frequency comparison with fractional uncertainty of 10-15

We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional uncertainty of less than 7×10^-16, making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg⁺)=1 064 721 609 899 145.30(69) Hz. PACS 06.30.Ft; 42.62.Eh; 32.30.Jc     

10~45 GHz宽频段同轴输入窗设计

为满足微波管放大器对宽频段输入窗的需求,并保证馈源的真空密封需求,提出并设计了一种适用于宽频段微波放大器的同轴输入窗。该宽频段同轴输入窗采用渐变圆环形陶瓷,材料介电常数为9.3,窗片厚度为2.5 mm, 内径为2.14 mm,外径为5 mm,渐变段长度为6.5 mm。利用三维高频电磁仿真软件CST对其建模分析,并对同轴内外结构尺寸和陶瓷渐变结构进行优化仿真,得出该宽频带同轴输入窗能够在10～45 GHz频带内实现插入损耗小于0.5 dB。     

10(-10) temporal contrast for femtosecond ultraintense lasers by cross-polarized wave generation

We take advantage of nonlinear properties associated with chi(3) tensor elements in BaF2 cubic crystal to improve the temporal contrast of femtosecond laser pulses. The technique presented is based on cross-polarized wave (XPW) generation. We have obtained a transmission efficiency of 10% and 10(-10) contrast with an input pulse in the millijoule range. This filter does not affect the spectral shape or the phase of the cleaned pulse. It also acts as an efficient spatial filter. In this method the contrast enhancement is limited only by the extinction ratio of the polarization discrimination device.     

5-10 GeV neutrinos from gamma-Ray burst fireballs

A gamma-ray burst fireball is likely to contain an admixture of neutrons. Inelastic collisions between differentially streaming protons and neutrons in the fireball produce nu(&mgr;) (nu;(&mgr;)) of approximately 10 GeV as well as nu(e) (nu;(e)) of approximately 5 GeV, which could produce approximately 7 events/year in km(3) detectors, if the neutron abundance is comparable to that of protons. Photons of approximately 10 GeV from pi(0) decay and approximately 100 MeV nu;(e) from neutron decay are also produced, but will be difficult to detect. Photons with energies less, similar1 MeV from shocks following neutron decay produce a characteristic signal which may be distinguishable from the proton-related MeV photons.     

Turbo Codes for 10-66GHz WiMax Systems

In this paper, performances of turbo codes for 10-66GHz WiMax system are analyzed and simulated. The channel of WiMax system is modeled as Rician channel due to the short wavelength. The uniform interleaver is used in the performance analysis to derive the average upper bound of performance of turbo codes. Simulations of bit error rate (BER) performances are performed for WiMax systems with/without turbo codes. It is shown that about 4.3dB coding gain can be achieved by using a [1,11/13,15/13] turbo code with 5 iterations, and thus the required transmission power of WiMax system can be decreased. It is also demonstrated that the performances of turbo codes are improved by increasing the interleaver length and the iteration number.