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本文对激光等离子体细丝的线性转换理论作了研究.通过对激光等离子体二次谐波的能量通量的计算发现,二次谐波的平面波理论关于在垂直密度梯度方向没有二次谐波辐射的结论与实验结果不符.在此基础上,我们提出了等离子体细丝的二次谱波线性转换理论,在垂直密度梯度方向有较强的二次谐波发射,这与实验结果较为一致. 相似文献
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将超声导波的非线性视为线性波动响应的一个二阶微扰,采用二阶微扰近似和导波的模式展开分析方法,从理论上研究了各向异性固体板中超声导波的二次谐波发生效应,给出了超声导波二次谐波声场的一般形式解.板材的各向异性可从多个方面对二次谐波发生效应产生影响,尤其是板材各向异性引起的导波模式相速度的改变,可显著地影响到构成导波二次谐波声场的二倍频导波模式随传播距离的积累增长程度.根据理论分析和数值计算结果可知,在不同传播方向上超声导波的非线性效应存在较显著的差异,伴随基频导波模式的传播所发生的二次谐波对固体板材的各向异性表现出更为敏感的性质,这一结果可为准确定征板材的弹性各向异性提供一种理论依据. 相似文献
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在考虑了二次谐波的吸收对转换效率影响的情况下,由光在介质中的波动方程,推导出负单轴晶体Ⅰ类相位匹配时平面二次谐波的耦合波方程和二次谐波转换效率的理论公式。在此基础上,再考虑走离效应的影响,给出了二次谐波转换效率的理论公式。根据这些公式,以负单轴晶体K2Al2B2O7(KABO)为例,对二次谐波的转换效率进行了数值计算。结果表明:考虑二次谐波的吸收时,存在倍频晶体长度的最佳值,当倍频晶体取该值时,二次谐波的转换效率最高;走离效应的存在使二次谐波的转换效率降低。 相似文献
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分别给出了归一化调制电流和电子束动能的积分微分方程,并提出了完整的数值计算方法。对于束压束流分别为511kV,5kA和800kV,8kA两组典型参数,采用非线性理论和二维粒子模拟程序分别计算了电流调制系数和距离的关系。在线性增长区以及当调制电流达到最大值并开始缓慢下降后,理论与模拟都符合得很好。此外还计算了电子束动能和调制电流的n次谐波的模式强度随归一化距离的变化情况:一次和二次谐波强度较大,八次以上谐波幅度较小而可以忽略。 相似文献
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A theory explaining the effects of second harmonic generation and rectification of space-charge waves (SCWs) in both space and time in photorefractive crystals and semi-insulating semiconductors is formulated for the first time. The theory predicts two mechanisms of SCW second harmonic excitation. An experimental technique is proposed for second harmonic detection, and the formulas required for interpreting the experimental results are derived. It is found that the effect of complete rectification of SCWs may lead to a change in the current passing through the sample by tens of percent. The results of calculations are in qualitative agreement with preliminary experimental results. 相似文献
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The frequency dependence of the third harmonic generation in trans-polyacetylene is quantitatively interpreted by considering the bands of finite chain and the damping of excitation. Our theory shows that there are two distinct peaks in the spectrum of the third harmonic generation. The first one around 0.6 eV comes from the three-photon resonant transition between the edges of the valence band and conduction band; the second one around 0.9 eV is produced by the two-photon interband transition. The excitation-dependent damping is essential to determine the position of the second peak. The theoretical results agree well with the experimental data. 相似文献
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U. K. Sapaev 《Optics and Spectroscopy》2003,95(1):154-157
A generalized approximation of strong interactions of waves is suggested for the theoretical analysis of second-harmonic generation under conditions of self-action. On the basis of the method suggested, approximate solutions for the efficiency of second-harmonic generation are obtained with regard to the influence of higher nonlinearities, depletion of pumping radiation, and linear phase mismatch. The effects of the phase mismatch and the spatial distribution of the amplitude of the fundamental harmonic on the efficiency of second harmonic generation by intense laser radiation is analyzed. The results obtained with the approximate method developed are shown to be in good agreement with known experimental data and numerical calculations. Optimum conditions for second harmonic generation are determined in a wide range of laser radiation intensity and at different spatial distributions of the fundamental harmonic amplitude. 相似文献
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This paper reports experimental and analytical results on optical second harmonic generation when a noncollinear arrangement is employed. The dependence of second harmonic power on crystal length, absorption, beam radius and the angle between the two fundamental waves is obtained. Double refraction of the crystal is taken into account, but the divergence and depletion of the fundamental waves are neglected. The results of the calculations are confirmed by experiments carried out with a KDP crystal in the near field of two intersecting TEM00 ruby laser beams.An extension of the theory to nonlinear interactions other than second harmonic generation - e.g. four-wave interaction - is possible. 相似文献
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S. D. Lavrov A. V. Kudryavtsev A. P. Shestakova L. Kulyuk E. D. Mishina 《Optics and Spectroscopy》2016,120(5):808-814
Second harmonic generation is studied in structures containing nanoscale layers of transition metal chalcogenides that are two-dimensional semiconductors and deposited on a SiO2/Si substrate. The second harmonic generation intensity is calculated with allowance for multibeam interference in layers of dichalcogenide and silicon oxide. The coefficient of reflection from the SiO2-layer-based Fabry–Perot cavity is subsequently calculated for pump wave fields initiating nonlinear polarization at every point of dichalcogenide, which is followed by integration of all second harmonic waves generated by this polarization. Calculated second harmonic intensities are presented as functions of dichalcogenide and silicon oxide layer thicknesses. The dependence of the second harmonic intensity on the MoS2 layer thickness is studied experimentally in the layer of 2–140 nm. A good coincidence of the experimental data and numerical simulation results has been obtained. 相似文献
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I. V. Shutov I. A. Ozheredov A. V. Shumitski A. S. Chirkin 《Optics and Spectroscopy》2008,105(1):79-84
Results of the study of second harmonic generation by femtosecond laser pulses in a lithium niobate crystal with a regular domain structure in the Laue scheme are presented. The angular distribution of the intensity and the polarization properties of the second harmonic radiation are studied. The orders of the corresponding phase-matching conditions and the angular width of the second harmonic maxima are calculated theoretically. The theoretical results are compared with experimental data. 相似文献
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On the baisis of a microscopic local-field theory, a non-local analysis of the second harmonic generation arising from intersubband transitions in coupled double quantum wells is presented. Taking as a start point an integral equation for the local field, the local fields at both the fundamental and second harmonic frequencies for a p-polarized incident field are determined. In a reflection geometry, the conversion efficiency of the second harmonic generation from the coupled double quantum wells is derived. Numerical calculations for different parameters show that the influence of the electronic non-local effects on the second harmonic generation can be significant. 相似文献
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研究了单模激光中产生的二次谐波的统计性质,用全饱和激光理论导出了二次谐波光子计数m的几率分布函数、二次阶乘矩和三次阶矩的表达式,同实验值比较,理论与实验在阈值附近符合得很好。研究结果表明,激光场基波和二次谐波的涨落随空腔衰减常数的增大而减小;当激光场中含有乘性噪声时,乘性噪声增强基波的涨落,同时抑制二次谐波的涨落。 相似文献
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The second harmonic generation at microwave frequency be a system of paramagnetic spins is studied. The correlations between different spins brought about by the e.m. field are taken into account, and a physical explanation is given to some features of the experimental results which could not be explained within the framework of the previously developed isolated spin theory. 相似文献
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A. V. Ovchinnikov O. V. Chefonov M. B. Agranat K. A. Grishunin N. A. Il’in R. V. Pisarev A. V. Kimel A. M. Kalashnikova 《JETP Letters》2016,104(7):441-448
Optical second harmonic generation at the photon energy of 2?ω = 2eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses (0.4–2.5 THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse arises through the electric dipole mechanism of the interaction of the electric field of a pump pulse with the electron subsystem of NiO. Temporal changes in optical second harmonic generation during 7 ps after the action of the pulse are also of an electric dipole origin and are determined by the effects of propagation of the terahertz pulse in a NiO platelet. Coherent oscillations of spins at the antiferromagnetic resonance frequency induced by the magnetic component of the terahertz pulse induce a relatively weak modulation of magnetic dipole optical second harmonic generation. 相似文献