共查询到20条相似文献,搜索用时 234 毫秒
1.
对超短超强激光脉冲 (45fs,6× 10 17W /cm2 )与光致电离氦气形成的欠稠密等离子体相互作用中的二次谐波辐射进行了实验研究。测量了多种打靶强度的飞秒激光脉冲与不同气体密度氦气相互作用的二次谐波光谱 ,得到在欠稠密等离子体中二次谐波辐射与打靶激光能量的关系 ,分析了产生二次谐波辐射产生的物理机制 ,在考虑了强短脉冲激光电离气体产生的等离子体径向电子密度梯度因素 ,基于非线性作用过程的理论预期曲线与实验结果较好地吻合 相似文献
2.
利用OMA光学多道分析仪测量了激光与薄膜靶相互作用中产生的辐射光谱,在靶后观察到红移的二次谐波发射. 这种二次谐波是v×B加热产生的、具有微脉冲结构的超热电子束在等离子体-真空边界产生的相干渡越辐射(CTR). 随着激光能量的增大,红移峰向长波方向移动,光谱同时发生展宽. 分析认为,等离子体临界面的迅速膨胀是导致二次谐波红移的主要原因. 随着预脉冲能量的增大,临界面膨胀速度增大,导致了发射峰更大的红移. 实验还测量了靶面法线方向的辐射光谱,观察到基频辐射的红移和展宽. CTR为诊断临界面的运动方向和速度提供了一种新的方法.
关键词:
相干渡越辐射
超热电子
超短超强激光
等离子体相互作用 相似文献
3.
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
4.
5.
6.
超短超强激光与固体靶表面等离子体相互作用可以通过高次谐波的方式产生从极紫外到软X射线波段的相干辐射,获得飞秒甚至阿秒量级的超短脉冲,可用于观测原子或分子中的电子运动等超快动力学过程.本文实验研究了相对论圆偏振飞秒激光与固体靶相互作用的高次谐波产生过程,实验结果表明,在较大入射角下,圆偏振激光也可以有效地产生高次谐波辐射.通过预脉冲控制靶表面的预等离子体密度标长,发现高次谐波的产生效率随密度标长的增加而单调下降.进一步通过二维粒子模拟程序,分析了激光的偏振以及预等离子体密度标长对高次谐波产生的影响,很好地解释了实验观测结果. 相似文献
7.
8.
9.
10.
11.
F. Setzpfandt D. N. Neshev A. A. Sukhorukov R. Schiek R. Ricken Y. Min Y. S. Kivshar W. Sohler F. Lederer A. T��nnermann T. Pertsch 《Applied physics. B, Lasers and optics》2011,104(3):487-493
We present theoretical and experimental studies on nonlinear beam propagation in lithium niobate waveguide arrays utilizing higher-order second harmonic bands. We find that the implementation of the higher-order second harmonic bands leads to a number of new effects. The combined interaction of two second harmonic bands with a propagating fundamental beam can lead to a complete inhibition of nonlinear effects or to the formation of discrete spatial solitons, depending only on the wavelength of the fundamental wave. Furthermore we analyze the properties of discrete solitons, allowing for linear coupling of the second harmonic. Here we predict and demonstrate experimentally a power dependent phase transition of the soliton topology. 相似文献
12.
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
13.
The second harmonic generated by non-linear self interaction of a magneto-acoustic wave in a planar plasma-filled waveguide is a freely propagating mode. Coupled-mode equations for resonant nonlinear interaction of this second harmonic mode with the fundamental mode are derived. Using these equations the possibility of generation of the second harmonic is analysed. 相似文献
14.
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
15.
The approximation of strong interaction of waves is developed to analyze the generation of the second harmonic under the conditions of self-action. Based on this method, an approximate expression is obtained for the generation efficiency of the second harmonic with allowance for the effect of higher nonlinearities, depletion of pumping radiation, and linear phase detuning. The effect of phase detuning and change in the spatial distribution of the amplitude of the fundamental radiation on the efficiency of second-harmonic generation has been analyzed. Good agreement of the results of the developed approximate method with experimental data and numerical calculations is shown. The optimum conditions of the second-harmonic generation in a wide range of the laser system radiation intensities are determined. 相似文献
16.
By using the generalized method of strong interaction of nonlinear waves and computer simulation, an analysis of the influence of self-action effects on second harmonic generation of an intense diverging picosecond pulse is performed. Using the approximation of strong wave interaction, an analytic solution is obtained for frequency conversion of the laser radiation taking into account the pump intensity depletion, the influence of the angular dispersion effect (ADE), and the higher nonlinearities. It is shown that the self-action effects, the ADE, and the linear phase mismatch can compensate for each other, increasing the efficiency of second harmonic generation. Optimum conditions for second harmonic generation in converging and diverging laser beams were found. An asymmetry of the angular dependence of the second harmonic intensity was experimentally observed and theoretically explained. The asymmetry is caused by the reverse energy conversion of the second harmonic into the pump by the influence of the ADE and Kerr nonlinearities. 相似文献
17.
提出了一种基于等效弹性模量的微裂纹-超声波非线性作用多阶段模型.该模型将微裂纹微观层面的界面几何特征和宏观层面的界面相对运动统一为介观单元弹性模量的变化,利用等效弹性模量表征损伤区域的"应力-应变",然后利用分段函数来描述微裂纹-超声波非线性相互作用,最后通过有限元仿真对波动方程进行求解,验证了模型的有效性,获得了超声波在经过微裂纹后传播的非线性波动规律.仿真结果表明本文提出的模型相比于双线性刚度模型、接触面模型,能更好地体现一个谐波周期内超声波经过微裂纹损伤区域时波形会发生畸变.同时,仿真实验还分析了裂纹倾角、裂纹长度和超声波激励幅值对超声波经过微裂纹后产生的二次和三次谐波的幅值的影响.最后,对比分析了该模型的仿真计算结果与实验测试结果,表明本文提出的多阶段模型与实验测试均能较好地体现微裂纹-超声波非线性作用产生的二次谐波信号,且结果基本一致,验证了模型的有效性.该模型为开展超声波非线性效应定量检测微裂纹提供了一种新的仿真手段. 相似文献
18.
The method of strong interaction of nonlinear waves has been developed to analyse the second harmonic generation of intense laser radiation in the transient regime. Analytic solution for frequency conversion efficiency – taking into account the pump radiation depletion, influence of phase mismatch, dispersion of group velocities and higher nonlinearities – has been first obtained. A comparison of theoretically derived results and known experimental data has been conducted, and a general agreement of these results has been obtained. The optimal conditions of the second harmonic generation of neodymium laser radiation into femtosecond pulse duration range have been determined. 相似文献
19.
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
20.
B. L. Vasin Yu. V. Korobkin M. V. Osipov V. N. Puzyrev A. T. Sahakyan A. N. Starodub S. I. Fedotov 《Bulletin of the Lebedev Physics Institute》2013,40(7):205-209
The experimental results on the conversion of multimode radiation of a neodymium glass laser with controlled spatial and temporal coherence to the second optical harmonic in nonlinear KDP crystal during the oee interaction implementation are presented. The dependence of the efficiency of the conversion to the second harmonic on the fundamental radiation power density on the crystal in the range I = 0.2 ? 5 GW/cm2 is studied at the number of transverse modes in the cavity N = 1000; the radiation divergence φ = 3.5, 4.7, and 5 mrad; the emission spectral width δλ = 5and 42 Å; and the pulse duration of 2.5 ns. The breakdown power density of the KDP crystal is determined, the interference properties of the converted radiation of the second harmonic are studied. 相似文献