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1.
基于模拟退火算法的自适应近场光束整形   总被引:6,自引:0,他引:6  
在激光实际应用中,为了提高系统的利用效率,常常需要将激光器的输出光束整形为特定光强分布光束.基于纯相位液晶空间光调制器的高空间分辨率、实时可编程控制等特性,结合模拟退火算法搭建了一套自适应近场光束整形系统.理论模拟了该系统对于理想高斯光束的近场整形效果,并基于这一闭环系统,对固体激光器输出的近高斯光束进行了近场光束整形...  相似文献   

2.
王锐 《发光学报》2014,35(7):835-839
为了有效抑制激光大气传输过程中引起的闪烁效应,本文围绕照明光束相干性与闪烁指数关系展开研究。首先,明确闪烁效应产生机理,建立与光束相干性相关的数学模型。然后,采用偏振分光元件将出射激光分为4束,并破坏其相干性。在此基础上,以随机相位屏为核心元件构建大气湍流仿真实验装置,评估不同光束相干性条件下的远场光斑闪烁指数。实验结果表明,4束光照明的光斑闪烁指数比单光束照明降低了75%。理论分析及实验结果均证明了多束部分相干光在抑制光强闪烁效应方面的有效性。  相似文献   

3.
为了获得高光束质量的脉冲固体激光输出,研究了高斯非稳腔固体激光器的模式分布。运用边界有限元法将谐振腔内光场衍射积分方程转化成矩阵方程组,模拟分析了平凸高斯非稳腔内光阑位置、孔径大小以及高斯镜参数对输出光束模式的影响。基于理论模拟结果对激光器结构参数进行了优化,分别测量了腔内不同光阑位置和孔径下的激光器输出光束振幅及模式分布情况。在光阑半径为1 mm、光阑距高斯镜为150 mm、泵浦电压为900 V的实验条件下,光束质量M_x~2=1. 9、M_y~2=2. 3,激光最大输出能量为280 mJ的高光束质量激光输出。实验结果表明,在腔内加入选模光阑以及优化高斯镜参数可以进一步改善腔内模式分布,获得高光束质量激光输出,这与理论模拟结果基本相符。  相似文献   

4.
大气湍流对部分相干平顶高斯光束的影响   总被引:4,自引:3,他引:1       下载免费PDF全文
采用相屏近似处理方法对激光通过湍流大气的传输进行了数值模拟。从数值模拟的结果拟合出两个公式:一是通过湍流前后部分相干平顶高斯光束的束宽平方比随阶数、传输距离和湍流强度的变化关系式;一是通过湍流后的相干长度随初始光束相干长度、湍流相干长度的变化关系式。研究发现:部分相干平顶高斯光束分解为相互独立的厄米-高斯光束的叠加;相干性越差的光束受到湍流的影响程度就越小;湍流对光束传输的影响与光束自身相干特性对其传输的影响之间是不相关的。  相似文献   

5.
谢兴盛 《大学物理》1990,9(11):47-47,F004
采用稳定腔的激光器所发出的激光,将以高斯光束的形式在空间传输.我们能够从已知的腔参数,推导出高斯光束的参数,就可以用透镜那样的光学元件来使一个腔的高斯光束同另一腔的高斯光束相匹配本文讨论两共轴高斯光束的匹配问题.  相似文献   

6.
拉盖尔-高斯光束由于其特有的涡旋特性使其在大气传输过程中具有更好的稳定性。实际激光输出存在的部分相干性将对光束传输具有明显的影响,在大功率输出模式下,克尔效应的产生也会影响到光束传输的特性。本文从部分相干拉盖尔-高斯光束的交叉谱密度方程出发,推导了克尔效应作用下光束的传输表达式,利用分步傅里叶变换,对高功率部分相干涡旋传输中的克尔效应过程进行了模拟,并对比了不同参数影响下,光束相干性不同时克尔效应的差异。结果表明,克尔效应有助于维持光强的环状结构,提高拓扑荷数能够有效地缓解因相干度降低而造成的涡旋结构衰退的现象。  相似文献   

7.
高增益激光器的模式和时间相干性   总被引:1,自引:1,他引:0  
耿纪宏  张桂燕 《光学学报》1994,14(5):80-485
以高斯型的功率谱模型为基础在理论上计算了高增益激光器的运转状态与光束的时间相干性之间的依赖关系。在实验上研究了CuBr激光的时间相干特性,并将计算结果与实验结果进行了比较。  相似文献   

8.
基于液晶空间光调制器的激光束整形   总被引:4,自引:1,他引:3  
于晓晨  胡家升  王连宝 《光学学报》2012,32(5):514001-138
采用相位混合算法(PMA)与平滑修正法相结合的混合算法,对激光发出的高斯光束进行整形,得到了均方误差和顶部不均匀度均明显降低的等光强分布。利用液晶空间光调制器(LCSLM)的相位调制特性,实现了对高斯光束的光束整形,获得了光强均匀分布的圆光束和矩形光束输出。得到的输出光束顶部不均匀度和均方误差都低于5%,能量集中度在90%以上。表明此方法是一种实时、可控和高效的激光束整形方法。  相似文献   

9.
利用Kogelnik一维耦合波理论,以及离散傅里叶变换,分析光栅矢量相互正交,且串联级联放置的两透射型体相位光栅对空域任意分布的连续激光光束的衍射特性;讨论其对入射光束的空间低通滤波性能,并具体模拟其对畸变高斯光束空间低通滤波的效果.结果表明,利用体光栅优良的角度选择特性,无须对畸变光束进行聚焦,即可实现入射光束角谱域中的高频成分与低频成分的空间分离,滤除畸变高斯光束中高频角谱成分,使得衍射光束与未畸变光束在空域中的光强分布非常接近,达到滤除畸变光束中杂散成分且保留有用成分的主要目的.这种方法有效地避免了聚焦型空间低通滤波,如针孔滤波在针孔附近光强过高,易致针孔周边材料损坏等不利因素,有助于应用至高功率激光光束质量的优化.  相似文献   

10.
 将多个光纤激光器的输出光束进行相干合成是获得高功率、高光束质量激光的有效途径。利用准部分相干光(PPCB)模型,计算了高功率光纤激光器阵列发出的部分相干光在远场的能量分布,分析了激光的时间部分相干性对相干合成的影响。计算结果表明,随着单根激光器输出光束线宽的增大,远场光斑的图样基本保持不变,但峰值功率和Strehl比随之减小。对于采用的算例,要保证远场光斑的Strehl比大于0.8,单根光纤激光器的线宽不能超过5 nm。  相似文献   

11.
This paper is based on the unified theory of coherence and polarization of stochastic electromagnetic beams and the extended Huygens–Fresnel principle, combined with the quadratic approximation of Rytov’s phase structure function and the generalized Stokes parameters. We have derived the novel expressions for the cross-spectral density matrix elements and the degree of cross-polarization of a class of elliptically polarized spatially and spectrally partially coherent Electromagnetic Gaussian-Schell model pulse (EGSMP) beams propagating through atmospheric turbulence along a slant path. Additionally, we calculate and analyze the effects of the turbulent intensity, the initial pulse duration, waist width of the beam, the spatial coherence length and temporal coherence length et al. on the polarization properties of fully polarized and partially coherent EGSMP beams. Finally, a comparison of the impact of those factors on the partially polarization beams is made. The results show that the influences of the turbulent intensity, the initial pulse duration, waist width of the beam, the spatial coherence length and temporal coherence length et al. on the polarization properties of fully polarized and partially coherent EGSMP beams are larger. While the effects of those parameters on the partially polarization and partially coherent EGSMP beams are smaller. It is noted that the results of this paper have established sound theoretical basis on the topic of improving performance of the laser system propagating through the atmospheric turbulence.  相似文献   

12.
In this paper, the spectral degree of coherence formula was derived by using the generalized Huygens–Fresnel principle and the method of Rytov phase structure function quadratic approximation. The spatial coherence of vortex Gaussian beams passed atmospheric turbulence was studied. It showed that the spatial coherence was mainly affected by the coherence of light source, the number of topological charges and the transmission distance. The distance of transmission was farther, the spatial coherence of beam was better. The number of topological charges were more, the spatial coherence of beam was better. In a certain transmission distance, the coherence of light source was better, the spatial coherence of beam was worse. In addition, there were coherent vortexes which spectral degree of coherence was zero after the partially coherent vortex beams getting through atmospheric turbulence transmission.  相似文献   

13.
基于广义惠更斯-菲涅耳衍射积分公式和洛伦兹函数的厄米-高斯展开,导出了部分相干洛伦兹-高斯光束在湍流大气中经傍轴ABCD光学系统的峭度参数的解析表达式,对该峭度参数进行了数值计算。结果表明:空间相干长度和结构常数对峭度参数的影响与部分相干洛伦兹-高斯光束本身的光束参数有关;当空间相干长度小于光束参数时,其影响显著;当洛伦兹部分的光束参数较大或高斯部分的光束参数较小时,结构常数的影响较明显且随传输距离的增大而增强。  相似文献   

14.
基于非Kolmogorov谱模型,利用广义惠更斯-菲涅耳原理和维格纳分布函数的二阶矩定义,推导出部分相干厄米高斯(H-G)光束在非Kolmogonov大气湍流中传输因子的解析表达式,并用以研究了非Kolmogorov大气湍流对部分相干H-G光束传输因子的影响。结果表明,部分相干H-G光束在非Kolmogorov大气湍流中传输时,传输距离、湍流外尺度、广义结构常量和空间相关长度越小,湍流内尺度和光束阶数越大,光束传输受非Kolmogorov大气湍流影响越小,光束质量越好。当广义指数取3.11时,部分相干H-G光束在传输过程中表现的光束质量最差。  相似文献   

15.
With the help of a tensor method, we derive an explicit expression for the on-axis scintillation index of a circular partially coherent dark hollow (DH) beam in weakly turbulent atmosphere. The derived formula can be applied to study the scintillation properties of a partially coherent Gaussian beam and a partially coherent flat-topped (FT) beam. The effect of spatial coherence on the scintillation properties of DH beam, FT beam and Gaussian beam is studied numerically and comparatively. Our results show that the advantage of a DH beam over a FT beam and a Gaussian beam for reducing turbulence-induced scintillation increases particularly at long propagation distances with the decrease of spatial coherence or the increase of the atmospheric turbulence, which will be useful for long-distance free-space optical communications.  相似文献   

16.
We study the change in the degree of coherence of partially coherent electromagnetic beam (so called electromagnetic Gaussian Schell-model beam). It is shown analytically that with a fixed set of source parameters and under a particular atmospheric turbulence model, an electromagnetic Gaussian Schell-model beam propagating through atmospheric turbulence reaches its maximum value of coherence after the beam propagates a particular distance, and the effective width of the spectral degree of coherence also has its maximum value. This phenomenon is independent of the used turbulence model. The results are illustrated by numerical curves.  相似文献   

17.
This work investigates the joint effects of jet engine exhaust-induced turbulence and atmospheric turbulence on the propagation of a partially coherent Gaussian Schell-model Array (GSMA) vortex beam. Using the two-process propagation method, analytical formulae are derived for the cross-spectral density, spectral density, degree of coherence, and beam width of the considered beam. The results show that the considered beam takes different shapes; when the spatial coherence is large, the spectral density of the GSMA vortex beam takes an elliptical shape, whereas when the spatial coherence is smaller, the spectral density remains a Gaussian shape. The evolution profile of the degree of coherence weakens gradually when the propagation distance, topological charge, and turbulence strength increase. Moreover, the profile of the degree of coherence takes the Gaussian profile when the propagation distance is longer or turbulence atmospheric is stronger. Furthermore, the results reveal that the corresponding beam spreads faster with a larger propagation distance, lower spatial coherence, and high-strength turbulence. This study also concludes from the results that the beam is affected more when its propagation is near the jet engine exhaust, which means that this latter has a significant impact.  相似文献   

18.
Normalized intensity distribution, the complex degree of coherence and power in the bucket for partially coherent controllable dark hollow beams (DHBs) with various symmetries propagating in atmospheric turbulence are derived using tensor method and investigated in detail. Analytical results show that, after sufficient propagation distance, partially coherent DHBs with various symmetries eventually become circular Gaussian beam (without dark hollow) in turbulent atmosphere, which is different from its propagation properties in free space. The partially coherent DHBs return to a circular Gaussian beam rapidly for stronger turbulence, higher coherence, lower beam order, smaller p or smaller beam waist width. Another interesting observation is that the profile of the complex degree of coherence attains a similar profile to that of the average intensity of the related beam propagating in a turbulent atmosphere. Besides the laser power focusablity of DHBs are better than that of Gaussian beam propagating in turbulent atmosphere.  相似文献   

19.
The explicit expression for the cross-spectral density of partially coherent elliptical Gaussian beams carrying an edge dislocation propagating through atmospheric turbulence along a slant path is derived, and used to study the transformation of the edge dislocation in atmospheric turbulence. We find that the edge dislocation disappears and transforms to a noncanonical coherence vortex, when partially coherent elliptical Gaussian beams with edge dislocation propagate through atmospheric turbulence. The inversion of the topological charge of the coherence vortex may take place. The ellipticity of the beam and slope of the edge dislocation play a dominant role in the evolution of the coherence vortex. In the coherent limit the coherence vortex in turbulence becomes an intensity vortex, however, differing from the case in free-space propagation, the position of the intensity vortex depends on the choice of the reference point. The results are illustrated analytically and numerically.  相似文献   

20.
大气湍流对部分相干电磁平顶光束传输的影响   总被引:1,自引:1,他引:0  
基于相干性和偏振性统一理论,采用Rytov相位结构函数平方近似推导出了部分相干电磁平顶光束在湍流大气中传输的偏振度、相干度和光谱强度公式,并研究了湍流对其传输特性的影响.研究表明,偏振度和相干度与源光谱的带宽无关.大气湍流使得不同阶数的部分相干电磁平顶光束的偏振度经长程传输后均趋于其初始值.大气湍流使得部分相干电磁平顶光束与电磁高斯一谢尔模型光束相干度的差别减小,并导致相干度的振荡和相位奇异现象消失.大气湍流使得相干性较好的部分相干电磁平顸光束的光谱跃变现象消失.  相似文献   

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