共查询到19条相似文献,搜索用时 140 毫秒
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针对一维非线性声波的传播问题进行了有限元仿真和实验研究. 首先推导了一维非线性声波方程的有限元形式, 含有高阶矩阵的非线性项导致声波具有波形畸变、谐波滋生、基频信号能量向高次谐波传递等非线性特性. 编制有限元程序对一维非线性声波进行了计算并对仿真得到的畸变非线性声波信号进行处理, 分析其传播性质和物理意义. 为验证有限元计算结果, 开展了水中的非线性声波传播的实验研究, 得到了不同输入信号幅度激励下和不同传播距离的畸变非线性声波信号. 然后对基波和二次谐波的传播性质进行详细讨论, 分析了二次谐波幅度与传播距离和输入信号幅度的变化关系及其意义, 拟合出二次谐波幅度随传播距离变化的方程并阐述了拟合方程的物理意义. 结果表明, 数值仿真信号及其频谱均与实验结果有较好的一致性, 证实计算方法和结果的正确性, 并提出了具有一定物理意义的二次谐波随传播距离变化的简单数学关系. 最后还对固体中的非线性声波传播性质进行了初步探讨. 本研究工作可为流体介质中的非线性声传播问题提供理论和实验依据. 相似文献
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推广T矩阵法来研究二组分颗粒复合介质的非线性交流响应,解析推导出基频、三次及五次谐波频率下的有效线性介电常数及三阶和五阶非线性极化率的解析表达式.当组分颗粒的介电常数为实数时,表达式同以前微扰理论完全一致.进一步数值计算了金属-电介质复合介质的有效非线性交流响应,数值结果表明,体系的三阶、五阶非线性极化率在表面等离子共振频率附近有明显增强,而且,随着体积分数提高,共振峰增强且伴随着共振频率红移现象.还进一步讨论了维度效应对体系非线性交流响应的影响.
关键词:
T矩阵方法
复合介质
非线性交流响应 相似文献
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二维矩形波导管中的非线性声传播 总被引:1,自引:0,他引:1
本文采用部分波和二阶微扰理论对二维矩形波导管内声波的非线性传播问题进行了研究。由二次谐波的边界条件和初始条件,可得到物理图象清晰、便于计算的二次谐波声场解析式。结果表明,不同基波传播模式间的相互作用不存在二阶非线性,管内任意振幅分布的稳态激发源产生的二次谐波为各个模式二次谐波之和,且二次谐波声场分布具有对称性。 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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Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a quantum box with finite confining potential 总被引:1,自引:0,他引:1
S. Ünlü . Karabulut H. afak 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):319-324
In this work, both the intersubband optical absorption coefficients and the refractive index changes are calculated exactly in a quantum box. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using the compact-density matrix approach. Numerical results are presented for typical GaAs/AlxGa1−x As quantum box system. The linear, third-order nonlinear and total absorption and refractive index changes are investigated as a function of the incident optical intensity and structure parameters such as box-edge length and stoichiometric ratio. Our results show that both the incident optical intensity and the structure parameters have a great effect on the total absorption and refractive index changes. 相似文献
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Guanghui Zhang Dong Xu Mengkai Lü Duorong Yuan Xingqiang Wang Fanqing Meng Shiyi Guo Quan Ren Minhua Jiang 《Optics & Laser Technology》2001,33(2)
Violet 404-nm radiation is generated by type-I single-pass frequency doubling of the output of an GaAlAs diode laser in critically phase-matched ZnCd(SCN)4 (ZCTC) crystal, a metallo-organic complex crystal. In this paper, its refractive index and second-harmonic generation phase-matching angles are reported. Using a 3-mm-long ZCTC crystal, a diode laser power of 473 mW generated 390 μW of second-harmonic radiation. More recently, 380-nm, 20 μW ultraviolet (UV) radiation is also realized by frequency doubling of the 100 mW output of a continuous-wave Ti:sapphire laser at 760 nm. ZCTC is a promising UV nonlinear optical candidate material for frequency doubling of diode lasers. 相似文献
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In this paper, we have analyzed the influences of non-linear refractive index on the four-wave mixing (FWM) characteristics in semiconductor optical amplifiers (SOAs). It has been shown that the generated FWM signal characteristics can be modified due to the variation of non-linear refractive index of the SOA's medium. The wave propagation in the SOA has been modeled using the nonlinear propagation equation taking into account gain spectrum dynamics, gain saturation, which depends on carrier depletion, carrier heating, spectral hole-burning, group velocity dispersion, self-phase modulation and two photon absorption. Simulation of optical wave evolution in the SOA has been carried out using the finite-difference beam propagation method (FD-BPM) both in time and spectral domains. Our simulation results confirm that higher FWM conversion efficiency and lower time bandwidth product are achieved for higher absolute values of non-linear refractive index. Moreover, non-linear refractive index is more efficacious for high power propagated waves in SOAs. Finally, we have studied the modification of waveguide refractive index due to the propagation of optical pulses. We have also shown that when |n2|=1 cm2/TW, refractive index variation is in the order of 10?4 to 10?7 for high and low power input pulses, respectively. 相似文献
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Dependence of Stokes dynamics in stimulated Brillouin scattering generated in optical fibers on the pump power, the nonlinear refractive index, the fiber length, and the feedback powers of the pump and the Stokes is numerically analyzed. The Stokes power fluctuation becomes complicated and chaotic as the nonlinear refractive index and the input pump power increase in a fiber of sufficient length. The Stokes dynamics is less complicated and the chaotic region decreases in a pump power-reflectivity domain in a short fiber. The chaotic behavior appears without regular tendency in relation to the feedback power. Taking into account the pump feedback, the chaotic region expands and some Stokes behaviors are different in the PP-R domain graph, compared with the case with the Stokes feedback alone, although this feedback does play an essential role in Stokes dynamics. 相似文献
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在10℃~230℃温差下,对大气相干长度r0分别采用夏克-哈特曼的到达角起伏法、差分像运动法、波面法三种测量法和四象限探测器进行了测试和对比;对折射率结构常量Cn2及闪烁功率谱分别采用夏克-哈特曼和光电倍增管进行对比.实验结果表明:对于r0,在强湍流时四象限探测器比夏克-哈特曼的稳定性明显降低,且对夏克-哈特曼三种方法,差分像运动法可克服设备抖动等问题,但引入了方向上不一致的问题,波面法可有效避免该问题;对于Cn2,夏克-哈特曼比光电倍增管测量更稳定,拟合相关系数高达0.96;对于闪烁功率谱,由于噪音影响,在200℃时夏克-哈特曼比光电倍增管测得的最大频率高15 Hz;最后,通过对夏克-哈特曼子孔径的闪烁功率谱分析得出,若同一子孔径入射光强不在CCD响应的线性区间时无法准确测量闪烁功率谱,否则可通过不同子孔径可完成湍流均匀性的测量.这将为湍流池提供最优的测试方法及理论依据. 相似文献
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Petrov V. Panyutin V. L. Tyazhev A. Marchev G. Zagumennyi A. I. Rotermund F. Noack F. Miyata K. Iskhakova L. D. Zerrouk A. F. 《Laser Physics》2011,21(4):774-781
We present measurements of the transparency, refractive index dispersion, nonlinear coefficient, damage threshold, and two-photon
absorption of mixed GaS
x
Se1 − x
crystals and show that GaS0.4Se0.6 is a promising nonlinear material for down conversion of pulsed 1064 nm radiation to the mid-IR above 5 μm without significant
two-photon absorption. 相似文献
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The values of the nonlinear refractive index n2 and the two-photon absorption coefficient β of ternary and quaternary ZnSe-based mixed crystals were extracted from the standard
backward degenerate four wave mixing (DFWM) and nonlinear transmission measurements at 532 nm, respectively. Studied crystals
were grown by the modified high-pressure Bridgman method. We found that the value of the nonlinear refractive index n2 for Zn0.79Be0.21Se is higher than that for Zn0.80Mg0.20Se. However, the opposite behaviour was found in the case of two-photon absorption coefficient β for these compounds. We also
found that the values of the nonlinear refractive index n2 and the two-photon absorption coefficient β for Zn0.83Be0.04Mg0.13Se are about five times lower and three times higher than that for Zn0.80Mg0.13Se, respectively. In the case of ternary ZnSe-based crystals we noticed that the value of the nonlinear refractive index n2
decreases with increasing Mg or Be content. However, the value of the two-photon absorption coefficient β increases with increasing
Mg or Be content. 相似文献
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The third order nonlinear optical properties of acid blue 29 solutions have been studied using Z-scan technique. Experiments are performed using a CW He–Ne laser at 632.8 nm wavelength and 3 mW power. The linear absorption coefficient α0, nonlinear absorption coefficient β, nonlinear refractive index n2, Re χ3, and Im χ3 are measured at three different concentrations. Our results show that higher concentration gives better nonlinear optical properties. Also, it was found that there is an increasing trend in the value of the nonlinear refractive index n2 as the concentration increases. 相似文献