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近期南海远程声传播实验数据的处理分析表明在深海不完整声道中声道轴以下存在一种会聚区,该会聚区相比于海面附近的上反转点会聚区在远距离处具有更高的会聚增益.本文利用射线简正波理论确定了水中反转型焦散线和海面反射型焦散线位置,对比发现实验中观测到的深海大深度会聚区位置与水中反转型焦散线位置一致,证明该会聚区是由大量简正波同相叠加形成的下反转点会聚区,其在深海声道轴以下的一定深度范围内都具有会聚效应,研究了该会聚区的形成条件以及声源深度变化对会聚区焦散结构的影响,对比了远距离处上下反转点会聚区的传播损失以及会聚区宽度,分析表明第七个下反转点会聚区的会聚增益仍不小于10 dB,研究了声速垂直结构变化对下反转点会聚区的影响,理论分析结果与实验数据吻合较好. 相似文献
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水下声道中的反转点会聚区(Ⅰ)简正波理论 总被引:3,自引:0,他引:3
本文用简正波方法讨论水下声道中反转点会聚区的声场。理论分析表明,反转点会聚区声场由大量的简正波同相叠加而成。在一定条件下,反转点会聚区的声强按r~(-2)衰减,会聚增益与会聚区号数无关,会聚区宽度与会聚区号数成正比,这些理论结果与Hale的实验一致。 在双直线声道情况下,会聚增益为此处a_1是相对声速梯度,k_0是波数,(h_0—z)是声源至声道轴的距离。 应用反转点会聚区的理论来分析水池模拟实验的结果,计算得到的表面声道中会聚区的位置、会聚增益以及会聚区宽度与实验结果一致。 相似文献
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本文给出快速判断光束会聚点位置的三种简便方法,即基于毛玻璃在光束会聚点附近的散班效应的散斑法和几何投影特性的阴影法,以及基于光栅在光束会聚点附近的衍射特性的光栅法。分析了各种方法的判断精度。结果表明,所给出的方法可方便地用于光路调整中光束,特别是激光束会聚点的准确判断 相似文献
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水下声道中一般有三类反转点,在它们附近形成不同类型的反转点会聚区。收、发深度不等的第Ⅲ类反转点会聚区的强度比前两类稍低,但其空间分布范围广泛,在低频远程声场中占有重要地位。本文着重讨论第Ⅲ类反转点附近的声场,给出了计算反转点附近以及焦散线声强的简明表式,提出了形成焦散线会聚的物理条件。理论分析表明,低频情况下第Ⅲ类反转点会聚区的声强与距离的平方成反比、与频率的1/3次方成正比。 相似文献
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高功率激光系统中鬼光束对元件安全造成威胁 ,并导致主光束质量变坏 ,故鬼光束会聚点的位置和鬼光束会聚光斑光强的定量分析 ,对高功率激光系统安全运行非常重要。根据高斯光束在共轴有限孔径光学系统中的传输变换规律 ,得到了平行光束和同心光束在共轴光学系统中的光斑传输变换公式 ,进而计算了高功率激光系统典型结构单元鬼光束会聚点的位置和鬼光束会聚光斑的光强。结果表明 ,共轴光学系统中鬼点分布都在光轴上 ,单元件构成的系统在未考虑增益介质放大时 ,鬼光束会聚光斑的光强随鬼点阶次的升高下降较快 ,而多元件构成的系统则规律性不明显。 相似文献
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会聚束电子衍射是测定晶体点群、空间群的有效方法。要清楚地判断会聚束电子衍射图样的对称性,电子束的会聚角要大,但衍射盘不能重叠。本文提出了一种新方法来获得不重叠的大角度会聚束电子衍射。新方法是使电子束离焦,固定样品,从而保留了样品的同心倾动位置,作大角度倾动时不会失去原来感兴趣的区域。新方法在原理上和田中等人提出的方法相同,但优越性更大。同时也研究了大束斑(≥2μm)大角度会聚束电子衍射。
关键词: 相似文献
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Characterization of semiconductor laser frequency chirp based on signal distortion in dispersive optical fiber 总被引:1,自引:0,他引:1
P. Krehlik 《Opto-Electronics Review》2006,14(2):119-124
In the paper, the simple method of laser chirp parameters estimation is presented. It is based on measuring time-domain distortions
of chirped signal transmitted through dispersive fiber and finding laser chirp parameters by matching measured distortions
to calculated ones. Experiments undertaken with 1.55 μm telecommunication grade distributed feedback (DFB) lasers and standard
single-mode fiber are described, together with some practical remarks on measurement setup and main conclusions. 相似文献
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采用无模激光器发射波长为330 nm的激光激发多色激光导星,需要考虑脉冲激光重频率、激光带宽、激光初始光斑直径以及大气透过率对回波光子数的影响.通过数值模拟,计算了高斯光束的脉冲激光和连续激光激发多色激光导星在实际大气中后向辐射330 nm和2207 nm波长的回波光子数.数值计算结果表明,在垂直发射和接收的情况下,当到达大气中间层的激光能量为1 W时,连续激光能够获得更多的回波光子数,并且回波光子数几乎无起伏.对于脉冲激光,提高脉冲激光重频率达到50 kHz以上时,多色激光导星330 nm的回波光子数随脉冲重频率的增加趋于有限值;当大气能见度小于5 km且大气相干长度为12.8 cm时,大约需要34 W以上的激光发射能量,才能获得满足使用自然星全倾斜探测的330 nm回波光子数.对于连续激光,相同情况下,大约需要20 W以上的激光发射能量. 相似文献
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对光纤激光极限功率的探索和其受限因素的分析, 有利于为大功率光纤激光器的发展提供理论依据和实验指导. 本文考虑热效应、光效应、非线性效应和抽运亮度等因素对光纤激光极限功率的影响, 分析了掺镱和掺铥光纤的极限功率和受限因素. 在此基础上, 结合激光在光纤中单模传输的条件, 计算了单模掺镱和掺铥光纤激光的极限功率. 计算结果表明, 在现有技术条件下, 使用常规的976 nm和793 nm激光二极管抽运, 单模掺镱和掺铥光纤激光的极限功率分别为4.2 kW和7.8 kW, 其中单模掺铥光纤激光的功率水平还远低于它的极限功率的原因是受抽运亮度的限制. 最后分析指出减小纤芯的数值孔径和改进少模光束的光束质量是提升单模光纤激光极限功率的重要途径. 相似文献
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A.F. Hassan M.M. El-Nicklawy M.K. El-Adawi E.M. Nasr A.A. Hemida O.A.Abd El-Ghaffar 《Optics & Laser Technology》1996,28(5):337-343
The two-dimensional Laplace integral transform technique is used to solve the problem of heating a semi-infinite target induced by the surface absorption of a laser pulse. Mathematical expressions for the surface temperature and the temperature profile within the target are obtained considering cooling and temperature-dependent absorption coefficient at the front surface. The linear behaviour of the system is found to be established for all cases except for that of temperature dependent surface absorptance. As an illustrative example, computations are carried out on Al, Cu, Ag and Au targets using an empirical formula for the temporal distribution of a measured laser pulse. 相似文献
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利用菲涅尔公式分析了Zig—Zag板条中全反射退偏对谐振光束的影响和能量损耗。分析了当谐振光偏振方向与Zig-Zag板条的选偏方向存在偏差时,线偏光经过板条后的偏振态,并计算了各因素对Zig—Zag板条全反射退偏损耗的影响。根据板条全反面的镀膜特点设计合理的谐振光全反射次数可有效地降低Zig—Zag板条的全反射退偏损耗。 相似文献
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This article presents new data on multicenter structure of the optical spectra and of emission dynamics of the doping ions in various types of crystalline and polycrystalline cubic laser materials (garnets, sesquioxides). It is inferred that the satellite structure of the active ions is induced by crystal field perturbations inside the near neighbor associations of the active ion with specific defects of the host lattice (P-type satellites independent on doping concentration) or with other active ions (M-type satellites dependent on doping concentration). Such satellite structures are described for various rare earth ions; including Nd3+, Pr3+, Er3+. In case of the garnet crystals, both types of satellites are present, and the satellites P can be connected with departures from stoichiometry; in garnet ceramics, they are much less intense. In contrast, the structures of M satellites are similar in garnet crystals and ceramics, indicating similar distribution of the doping ions in the host matrix. The luminescence spectra of these materials are influenced by the emission quantum efficiency of the various centers. In the case of sensitized materials, the mutual crystal field perturbations could modify the absorption spectra on both the sensitizer ions. In the case of materials with charge compensation, the electric charge disordering determined by the process of compensation strongly influences the optical spectra of the doping ions and their distribution. The relation between the global spectroscopic properties and those measured by microscopic methods is also considered. The connection between the fabrication process, structure, spectroscopic, and laser emission properties is shown and it is inferred that the multicenter structure of the spectra, together with emission dynamics, can be an efficient tool for investigating the microstructure of the laser materials, for optimization of laser properties, or for tailoring new laser materials. 相似文献
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C.J. Zietkiewicz B.A. Knecht C.M. Herring N.P. Ostrom J.G. Eden 《Optical and Quantum Electronics》2002,34(10):1031-1044
The design, construction, and operating characteristics of a pulsed, transverse discharge-pumped HgBr laser, capable of operation at pulse repetition frequencies as high as 100 Hz, are presented. Having an active length of 53 cm, this laser system is preionized by two sets of spark arrays and average single pulse energies of 55 mJ are produced from Ne/N2/HgBr2 (natural abundance) vapor mixtures, with an output coupling of 50% and 17 J of energy stored in the pulse forming network. Based on measurements of the laser pulse energy for several values of cavity output coupling, the small signal gain coefficient and saturation intensity for the laser were determined to be 4.7% cm–1 and 260 kW cm–2, respectively. The single pass gain-to-loss ratio is 12.4. 相似文献
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