共查询到19条相似文献,搜索用时 660 毫秒
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高功率激光放大器中光束的成丝和B积分 总被引:13,自引:4,他引:9
研究了高功率激光放大器中光束的成丝问题,利用弗兰兹-诺德威克(Frantz-Nodvik)模型将准稳态波动议程推广到介质有饱和增益的情形,进而得到高功率激光放大器中小尺度调制的传输方程,在小信号增益和饱和增益情形下,分别得到了小尺度调制方程的精确解析解和数值解。结果表明,对于相同的输入光强,增益使小尺度调制增益谱的范围加宽,最快增长频率增高,最大增长率提高;同时,在放大介质中,小尺度调制的最快增长频率和最大增长率还随传输距离变化,增益饱和效应使小尺度调制的增长速度以及B积分的增长低于无饱和放大情形。 相似文献
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在物体变形场的测量中,云纹干涉的载频调制技术有重要作用.在云纹干涉中,对称光照明产生的衍射光沿试件栅表面的法线传播并产生干涉.通过改变照明光的入射角度,可实现变形条纹场的空间调制.通过光程差的分析说明了载波条纹产生的机理,得出了载波频率与照明光入射角度变化之间的关系式.利用三点弯曲加载结合二维载频调制实验,给出了实验结果.证明了在初始条纹较少的情况下,载频调制技术能有效地测量物体的位移场. 相似文献
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为避免时域调制增长形成的高强度时间尖峰对光学元件的损坏,数值研究了啁啾堆积脉冲宽带激光非线性传输的时域调制增长规律。结果表明:对于正常色散介质,子脉冲间干涉引入的时间调制与外加调制随着传输距离的增加,不断振荡减弱;相反,对于反常色散介质,无外加时间噪声时,堆积子脉冲间的相互干涉引入的时间调制有微弱增长,但当传输距离进一步增加时,子脉冲间干涉引入的调制可以获得快速增长;而当外加非线性最快增长时间调制时,时间调制发生迅速增长,具有破坏威胁的时间尖峰易于形成。 相似文献
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干涉条纹的相位变化与干涉条纹中某一固定点的光强密切相关,基于这一原理,通过对干涉场光强分析,提出并设计了一种用于干涉条纹相位锁定的控制系统.光电探测器检测干涉条纹中固定目标点的光强,并以该光强电压作为反馈控制信号,利用声光调制器对干涉系统中两束高斯光束中的一束进行实时频率调制,将光强电压控制在一个固定值,实现干涉条纹的相位锁定.构建了条纹锁定控制系统控制对象的理论模型,通过实验进行了验证,并基于该模型的特点设计了条纹锁定控制器.实验结果表明:在400Hz的控制频率下,干涉条纹相位漂移不超过±0.04个条纹周期,满足干涉光刻的曝光需求. 相似文献
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进行穿透扫描探测实验时,在回波图像中发现了由于介质具有倾斜角度产生的周期性干涉条纹,这种干涉条纹对介质后或者介质中的目标成像有严重影响.研究表明,这种干涉条纹主要由介质表面反射波及透射后的层面反射波引起.文中建立点源辐射模型分析干涉条纹现象的形成机理,推导出薄层介质的干涉条纹间距表达式.考虑到天线的影响,建立了角锥喇叭天线近场模型,并且基于该模型进行精确的电磁仿真.商用软件Computer SimulationTechnology的电磁仿真结果与MATLAB程序的数字计算结果进一步验证了干涉条纹的成因分析及其与介质倾斜角度的关系.从推导的薄层介质干涉条纹间距表达式可以看出,干涉条纹间距与介质倾斜角度有关,控制影响条纹间距的因素,可以抑制干涉条纹现象,从而达到提高目标分辨率和成像质量的效果. 相似文献
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大剪切电子散斑干涉的载频调制与位移场测量 总被引:6,自引:0,他引:6
将电子散斑干涉场的载波调制引入到大剪切电子散斑干涉中,通过对参考物的微小偏转引入载波条纹;利用傅里叶变换法,解调出了变形场的相位,从而实现了物体变形场的精确测量。讨论了大剪切载频的调制机理,理论分析表明,调制条纹的空间频率与参考面偏转的角度成正比;因此,控制参考面的偏转角度可实现不同位移量系统的调制。利用中心加载周边固定圆盘进行了典型实验,实验结果证明在大剪切电子散斑干涉技术中可以通过参考面的旋转高质量地实现电子散斑干涉条纹的调制,求解位移场。该系统具有系统简单,不需要专门引入参考光,条纹质量好等优点。该技术可扩展电子散斑干涉的应用范围,有一定的实际应用价值。 相似文献
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基于非线性薛定谔方程推导出大啁啾脉冲的传输方程,利用微扰理论,分析了啁啾脉冲激光的时空不稳定性. 理论上比较清楚的阐述了宽带脉冲激光在大啁啾情况下,其时空噪声的相互影响与相互作用情况及脉冲啁啾对噪声微扰调制的影响,发现在相同γI0(非线性系数与峰值强度乘积)的情况下脉冲啁啾对噪声调制的增长没有直接影响. 最后我们在实验上利用非线性介质对啁啾脉冲的空间小尺度自聚焦过程进行了部分验证,同时也在数值上对宽带啁啾脉冲的时间噪声调制的增长进行了模拟分析,发现实验结果和模拟分析结论
关键词:
时空不稳定性
宽带脉冲激光
啁啾 相似文献
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We describe a method to increase and to reverse the contrast of the fringes generated in a Fresnel plane by a photographic plate H, multiple exposed to a random intensity distribution and laterally shifted through ζH between the exposures. H is limited by two identical apertures separated through 2ζ0. It is demonstrated that the contrast of the fringes is a function of ζH and ζ0. The cases of the two-beam fringes and of the multiple-beam fringes will be considered. 相似文献
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Shape measurements by fringe projection methods require high-quality sinusoidal fringes. We present a sinusoidal fringe generation technique that utilizes slightly defocused binary fringe projection. The proposed method is a spatial version of the well-known pulse-width modulation (PWM) technique of electrical engineering. PWM is easy to implement using off-the-shelf projectors, and it allows us to overcome the gamma problem (i.e., the nonlinear projector response) in the output light intensity. We will demonstrate that, with a small defocusing level--lower than with other techniques proposed in the literature--a high-quality sinusoidal pattern is obtained. Validation experiments using a commercial video projector are presented. 相似文献
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Tianlun Li Rui Hao Yaping Hou Duorui Gao Yunfan Xu Yanpeng Zhang Jixiang Fang Lei Zhang 《Annalen der Physik》2023,535(1):2200378
A type of MoS2 nanoparticle with a spherical-like shape is chemically synthesized with favorable third-order and suppressed second-order nonlinear optical response, which results from the isotropy induced by the geometrical uniformity of nanoparticles and an artificial symmetry center. It is found that the linewidth of third harmonic signal is broadened due to the self-phase modulation effect, another third-order nonlinearity. Moreover, the intensity of harmonic signal can be conveniently adjusted by controlling the polarization state of applied optical field. The artificially designed material morphology may provide a reference for designing all-optical modulation devices. 相似文献
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In this paper we have measured second order nonlinear refractive index of Ag and Au nano-particles using the moiré deflectometry with a CW He-Ne laser at wavelength of 632.8 nm. The main advantages of this technique are its extreme experimental simplicity and low sensitivity to external distribution in comparison with other interfrometric methods that need very stable experimental set-up. Because of self-focusing (or self-defocusing) that is due to intensity dependent refractive index, presence of sample in the moiré deflectometry set-up lead to rotation of moiré fringes. By moving the sample in set-up we have measured these rotation angles in different displacements from focus point of lens used in this set-up and then we have calculated the nonlinear refractive index of Ag and Au nano-particles using their values. Also we have obtained the sign of n2 regard to the direction of rotations. Consequently by using the Mathematica software we have exhibited the suitable fitness of theoretical curve with experimental results. 相似文献
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A new approach for studying photorefractive gratings in two-wave mixing experiments by a phase modulation technique is presented. The introduction of a large-amplitude, high-frequency sinusoidal phase modulation in one of the input beams blurs the interference pattern and provides powerful harmonic signals for accurate measurements of the grating diffraction efficiency η and the output phase shift ϕ between the transmitted and diffracted waves. The blurring of the light fringes can be used to suppress the higher spatial harmonics of the grating, allowing a space-charge field with sinusoidal profile to be recorded. Although the presence of such a strong phase modulation affects the beam coupling in a rather complicated way, it is shown that for the special case of equal intensity input beams, the effect of the phase modulation on η and ϕ is reduced to a weakening of the coupling strength. The potentialities of the technique are illustrated in a study of refractive-index waves excited by running interference patterns in a Bi12TiO20 crystal. Expressions for the diffraction efficiency and the output phase shift are derived and used to match numerically calculated curves to the experimental data. The theoretical model is supported by the very good data fitting and allows the computation of important material parameters. PACS 42.40.Ht; 42.40.Kw; 42.70.Nq 相似文献
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Using the intensity distribution of interference fringes formed by a capillary filled with transparent liquid, the variations in refractive index (RI) of nonlinear optical materials, corresponding to change of the intensity at the centre of fringes for a period, were deduced. With this conclusion, we measured variations in RI of ethyl red (ER) solution excited by a 535-nm-15 mW-laser, and found that the change of RI is 0.00504 and the corresponding effective index of refraction is −1.06 × 10−9, for which the order of magnitude is same as that measured by Z-scan. The influences on the accuracy of the method, such as temperature, beam and fringe contrast, were analyzed. This is a novel and simple method for measuring the RI of nonlinear optical materials. 相似文献
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KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries (e.g., width, morphology, and depth of defects) are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 μ. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μ for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects. 相似文献