激光大气传输中的相位奇点和光学涡旋及其演化特性研究

发布时间：2017-12-31 14:16

本文关键词：激光大气传输中的相位奇点和光学涡旋及其演化特性研究　出处：《山东师范大学》2016年博士论文　论文类型：学位论文

【摘要】：激光在湍流大气中传输时,光波的振幅和相位会发生随机起伏,导致接收平面处光场的光强起伏及相位畸变等。在强湍流效应条件下,畸变光场中会出现一些光强为零且相位不确定的点,这些点被称为相位奇点。相位奇点的存在给传统自适应光学系统的波前测量和校正带来很大困难,从而给天文观测、激光通讯、激光武器等众多的工程应用带来挑战。为了提高自适应光学系统的校正能力,有必要对激光大气传输中的相位奇点演化特性展开研究。中心光强为零且携带有相位奇点的涡旋光束因其特有的性质受到人们的广泛关注。当涡旋光束在湍流大气中传输时,传输介质会引起光强起伏、光束扩展以及光学涡旋的漂移等。另外,涡旋光束的拓扑荷可以作为信息的载体用于自由空间光通信中。因此,有必要研究涡旋光束在湍流大气中的光强分布、光束扩展以及光学涡旋的演化特性等。本论文首先研究了激光在大气中水平、斜程、上行和下行传输时,受湍流扰动的畸变光场中产生的相位奇点的演化特征;然后以拉盖尔-高斯涡旋光束为例,系统研究了涡旋光束在湍流大气中传输时的光强分布、光束扩展、涡旋光束拓扑荷的确定和光学涡旋的漂移等传输特性;最后简单探讨了无衍射贝塞尔光束在湍流大气中的束宽扩展和相位奇点数密度的变化特性。主要研究内容和结论如下:1.数值模拟了激光在大气中传输时,受湍流扰动的畸变光场中产生的相位奇点的演化特征。模拟结果显示,相位奇点会成对产生;极性相反的相位奇点对会随着波前向前传播;相位奇点对的相对位置和间距在传播过程中会发生变化;相位奇点也会成对地湮灭。2.数值模拟了激光在湍流大气中水平传输时产生的相位奇点数密度与湍流效应特征参数的关系,这些参数包括传输距离,湍流强度,激光波长、湍流内尺度和外尺度等。计算结果表明,当其他传输条件一定时,相位奇点数密度分别随传输距离的增加和湍流强度的增强而增加,随湍流内尺度和激光波长的增加而降低;而相位奇点数密度基本不受湍流外尺度的影响。3.数值模拟了激光在湍流大气中水平传输时两种传输条件下的相位奇点数密度的变化过程。一种是湍流较弱但传输距离很长;另一种是传输距离较短但湍流很强,这两种情况下均能产生强湍流效应。结果表明,湍流强度对相位奇点数密度的影响要大于传输距离对相位奇点数密度的影响;不同传输条件下产生的相位奇点数密度随Rytov指数的变化过程有所不同,但它们之间的关系比较符合Logistic统计公式。4.模拟了激光在湍流大气中自地面向空中垂直上行传输时畸变光场中出现的相位奇点数密度随传输高度的变化过程。在传输高度一定的情况下,主要模拟了两种激光传输过程:一种是固定发射激光的波长,变化传输路径中的湍流强度;另一种是固定传输路径中的湍流强度,变化发射激光的波长。结果表明,相位奇点数密度随传输高度的增加其变化过程可以分成四个不同的区域;当发射激光的波长一定时,近地面处的湍流强度不同对应的相位奇点数密度达到峰值时的传输高度也是不同的,湍流越强,相位奇点数密度的峰值越高,其对应的传输高度却越低;当湍流强度的分布一定时,畸变光场中的相位奇点数密度达到峰值时对应的传输高度基本不受激光波长的影响。另外,通过对模拟结果的曲线拟合发现,不同条件下的相位奇点数密度随传输高度的变化关系非常类似于黑体辐射公式。5.模拟了激光在湍流大气中自地面向空中斜程传输时,相位奇点数密度的变化特征。结果表明,斜程传输时的相位奇点数密度随传输距离的变化过程非常类似于上行传输时相位奇点数密度随传输高度的变化过程;固定近地面处的湍流强度,当传输距离一定时,光束的发射天顶角越大,畸变光场中出现的相位奇点数密度越大且相位奇点数密度达到极大值时对应的传输距离越长;当发射天顶角和传输距离一定时,近地面处的湍流强度越强,畸变光场中产生的相位奇点数密度越大。6.模拟了激光在湍流大气中自空中某一高度垂直下行传输至地面时,畸变光场中产生的相位奇点数密度的变化特征。结果表明,光源位置距离地面越高,在较高位置处的畸变光场中就会有相位奇点产生,且到达地平面处时的畸变光场中产生的相位奇点数密度越大;相位奇点数密度随高度的降低而单调增加且在接近地平面处达到最大值。7.以拉盖尔—高斯(LG)光束为例,模拟了涡旋光束在湍流大气中传输时在垂直于传输方向的平面内的光强分布。结果表明:当涡旋光束在湍流大气中传输时,光强由最初的中空光束演变为平顶光束,并最终在远场演变为高斯光束。光强廓线的演变过程以及相位奇异性的消失与传输距离、湍流强弱、湍流外尺度、涡旋光束拓扑荷数、光束的束腰宽度以及光束的波长有关,而与湍流的内尺度无关。对于同一涡旋光束,传输距离越远、湍流越强以及湍流外尺度越大,光强分布受到的影响越大。对于不同的涡旋光束,拓扑荷数越高、束腰越窄以及波长越长,光强分布受到的影响越小,在湍流大气中越易于保持其原有的光强和相位分布特性。8.数值模拟了大气湍流对涡旋光束束宽扩展的影响。结果表明:传输距离越长或湍流越强,涡旋光束在湍流大气中传输时的束宽扩展受湍流的影响越大;涡旋光束的拓扑荷数越高、光束的束腰越小或光波的波长越长,束宽扩展受大气湍流的影响反而越小;随着湍流内尺度的减小或湍流外尺度的增加,大气湍流对光束扩展的影响会有所增加,但影响幅度相对较小。另外,还比较了涡旋光束和普通高斯光束因湍流引起的光束扩展的差异。结果表明大气湍流对普通高斯光束束宽扩展的影响要大于对涡旋光束束宽扩展的影响。9.通过数值分析接收面内相位奇点拓扑荷的代数和(简称为AS-PS),得出AS-PS近似等于入射涡旋光束拓扑荷的结论。提出了一种在湍流大气中确定涡旋光束拓扑荷的方法——相位奇点代数和法。该方法可以有效的消除湍流的影响并减小确定拓扑荷的误差。研究了传输参量、光束参量以及探测系统的口径等对确定AS-PS的影响。结果表明:涡旋光束在湍流大气中的传输距离越短、湍流强度越弱、入射涡旋光束的拓扑荷越低,利用该方法确定涡旋光束拓扑荷的标准偏差越小;合理选择涡旋光束的束腰也会增加该方法的准确性;探测口径近似等于涡旋光束传输至探测面上的主光斑尺寸时,相位奇点代数和与入射涡旋光束拓扑荷的相对误差最小,该结论可以给探测器口径的定量设计提供一定的参考依据。10.通过模拟光学涡旋在接收面的不同位置出现的频次研究了湍流大气中光学涡旋的漂移特性。由模拟结果可知,光学涡旋在接收面的不同位置出现的频次或概率满足高斯分布。随着传输距离的增加、湍流的增强或入射涡旋光束拓扑荷的增加,光学涡旋位置的统计特性不再满足高斯分布。另外,适当选择入射涡旋光束的束腰会减小光学涡旋的漂移。以上这些结论可以为涡旋光束在自由空间光通讯中的应用提供一定的参考依据。11.初步探讨了贝塞尔光束在湍流大气中传输时引起的束宽扩展和相位奇点数密度的变化特性。结果表明,与零阶贝塞尔光束和零阶贝塞尔—高斯光束相比,贝塞尔—高斯涡旋光束由大气湍流引起的束宽扩展程度最小且在一定条件自身所携带的光学涡旋基本不受湍流的影响,即贝塞尔涡旋光束更适用于自由空间光通信中信息的载体。
[Abstract]:Laser propagation in turbulent atmosphere, the amplitude and phase of light will lead to random fluctuations, receiving plane light field intensity fluctuation and phase distortion. In effect under the condition of strong turbulence, there will be some distortion intensity is zero and phase uncertain point light field, these points are called phase singularities. There is a phase singularity which brings great difficulties to the traditional adaptive optics wavefront measurement and correction to the astronomical observations, laser communication, laser weapon engineering and many other challenges. In order to improve the correction capability of adaptive optical system, it is necessary on the evolution properties of phase singularities of laser transmission in the atmosphere is studied. The intensity of the vortex center beam zero and carrying phase singularities have attracted extensive attention due to its unique properties. When the vortex beam propagation in turbulent atmosphere, the transmission medium will cause the intensity fluctuation Well, the beam spreading optical vortex drift. In addition, the topological charge of vortex beam can be used as the carrier of information for free space optical communication. Therefore, it is necessary to intensity distribution in the turbulent atmosphere of vortex beam, beam propagation and optical vortex evolution characteristics. This paper studied the laser level in the atmosphere in the slant, the uplink and downlink transmission, the evolution characteristics of light field distortion in phase singularities by turbulence perturbation; then the Laguerre Gauss vortex beam as an example, the light intensity distribution of vortex beams in atmospheric turbulence is studied systematically on the beam spreading, transmission characteristics and determine the topology of optical vortex vortex beam bearing the drift; finally discusses the characteristics of non diffraction Bessel beam in turbulent atmosphere beam width extension and phase number of singular points density. The main research contents and conclusions are as follows 1.: the numerical simulation of laser propagation in atmosphere, the evolution characteristics of light field distortion in phase singularities by turbulence disturbance. The simulation results show that the phase singularities will be produced in pairs; the opposite polarity of phase singularities with wavefront propagates; phase singularities of the relative position and distance change in communication in the process of relationship; phase singularities will pair annihilation.2. numerical simulation of the laser generated in a turbulent atmosphere, the odd number phase density and turbulence parameters, these parameters include the transmission distance, turbulence intensity, laser wavelength, turbulence inner scale and outer scale. The calculation results show that when the other transmission conditions when a certain number of singular points respectively with increasing phase density and turbulence intensity of the transmission distance increased, and decreased with increasing turbulence inner scale and laser wavelength; and the number of dense phase singularities The degree is not affected by the outer scale of turbulence numerical simulation of the effect of.3. laser in horizontal turbulent atmosphere, changes of two kinds of transmission under the condition of the phase number of singular points density. One is the weak turbulence but the transmission distance is very long; the other is a short transmission distance but the turbulence is very strong, these two kinds of situations can produce strong turbulence effect. The results show that the influence of turbulence intensity on the phase density is greater than the number of singular points affect the transmission distance of the phase change process of the odd number density; different transmission conditions of phase number of singular points density with Rytov index is different, but the relationship between them is consistent with the Logistic statistical formula.4. to simulate the change with the height of the process of laser transmission in atmospheric turbulence from the ground to the air vertical upward distortion in the light field transmission phase. When the number of singular points density transmission height, main mode The two laser transmission process: one is the fixed laser wavelength, the turbulence intensity change of the transmission path; the other is a fixed transmission path in turbulence intensity, changes in emission wavelength of the laser. The results show that the phase number of singular points density with the increase of the height of the transmission process can be divided into four different when the wavelength of the laser emission region; when the transmission of near ground surface turbulence intensity corresponding to the different phase of odd points density peak height is different, the stronger the turbulence is, the peak phase number of singular points density is higher, the corresponding transmission height is lower; when the turbulence intensity distribution at the corresponding transmission in distorted optical field phase singular points density peak height was not affected by the wavelength of the laser. In addition, the curve fitting of the simulation results showed that under different conditions of phase singular points density With the change of the height of the transmission relationship is very similar to the blackbody radiation formula.5. simulation of laser beam propagation in turbulent atmosphere from the ground to the air oblique propagation, phase change characteristics of odd points density. The results show that the oblique propagation of phase singular points density change with the transmission distance of the process is very similar to the uplink transmission phase odd the number density changes with the height of the transmission process; the turbulence intensity is fixed near the ground, when the transmission distance, the beam emission zenith angle increases, appear distorted optical field phase in the odd points greater density and phase singularity density reached the maximum when the corresponding transmission distance is longer; when the zenith angle of emission and the transmission distance, turbulence intensity near the ground surface is stronger, the distortion of light field phase in the number of singular points higher density.6. simulation of laser beam propagation in turbulent air from a vertical downward transmission To the ground when the number of singular points density variation of phase distortion in the light field. The results show that the position of the light source from the ground is higher in the high position of the distorted optical field will produce phase singularities, the distortion of phase singularities in the light field density and arrived at the plane of the larger phase; the odd points density with height decrease monotonously increased and near the ground plane reaches a maximum at.7. (LG) with Laguerre Gauss beam as an example, the simulation of the vortex beams in atmospheric turbulence intensity in the plane perpendicular to the direction of transmission in distribution. The results show that when the vortex beam propagating in turbulent atmosphere when the light intensity changes from the original hollow beam of flat topped beam, and eventually evolved into the Gauss beam in the far field. The evolution of intensity profile and the phase singularity and the disappearance of the transmission distance, turbulence intensity, turbulent outer scale vortex. Optical beam topological number, the beam waist width and beam wavelength, and has nothing to do with the inner scale of turbulence. For the same vortex beam, the transmission distance is far more turbulent intensity and turbulent outer scale is larger, the greater the effect of light intensity distribution. For different vortex beam, the topological charge of the high waist is narrow and the longer wavelength, the intensity distribution of the effect is small, easy to maintain its original intensity and phase distribution of.8. numerical influence of atmospheric turbulence on the vortex beam width spreading in a turbulent atmosphere were simulated. The results show that the transmission distance is longer or more strong turbulence, vortex beams propagating in in the turbulent atmosphere when the beam width is more affected by turbulence; topological charge of vortex beam with higher beam waists smaller or longer wavelength, the beam width extension affected by atmospheric turbulence decreases with the turbulence inner scale; Increase or the decrease of the outer scale of turbulence, the influence of atmospheric turbulence on the beam spreading will increase, but the influence is relatively small. In addition, also compared the difference of beam vortex beams and ordinary Gauss beam due to turbulence induced expansion. The results show that the influence of atmospheric turbulence on the ordinary Gauss beam width spreading is greater than the expansion of the vortex the beam width effect of.9. through numerical analysis of in-plane phase singularities receiving algebraic and topological charge (referred to as AS-PS), the AS-PS is approximately equal to the topological charge of the vortex beam incident. The conclusion presents a method of determining the topology in the atmospheric turbulence vortex beam bearing - phase singularities and algebraic method. This method can be effective to eliminate the effects of turbulence and reduce the error of determining the topological charge. The transmission parameters are investigated, and the effects of the beam parameters detection system to determine the diameter of AS-PS. The results show that the vortex The propagation distance in the turbulent atmosphere is shorter, the turbulence intensity is weaker, the topological charge of vortex beam incidence is low, determine the standard deviation of the topology of vortex beam bearing using this method; reasonable choice of vortex beam waist will also increase the accuracy of the method; detection aperture is approximately equal to the spot size of vortex beam transmitted to the main on the surface of the probe, and the relative error of phase singularities of algebraic and topological charge of the vortex beam incident is minimum, the conclusion can give the quantitative design of detector aperture and provided a reference for the.10. simulation of optical vortex research in receiving the different position of the frequency drift characteristics of the optical vortex in a turbulent atmosphere. From the simulation results the frequency, or probability of optical vortex in different position of the receiving surface satisfies Gauss distribution. With the increase of the transmission distance, enhanced or incident optical vortex turbulence Increase the beam topological charge, the statistical properties of the optical vortex position no longer satisfies Gauss distribution. In addition, will reduce the incidence of optical vortex vortex beam waist appropriate selection drift. These conclusions can be used as vortex beams in free space optical communication to provide a reference for.11. discussed the characteristic changes caused by Bessel beam transmission in the turbulent atmosphere when the beam width extension and phase number of singular points density. The results show that, compared with the zero order Bessel beam and zero order Bessel Gauss beams, Bessel - Gauss vortex beams by atmospheric turbulence caused by the beam width of the optical vortex and its extended degree minimum carried under certain conditions is not affected by turbulence the carrier, namely Bessel vortex beam is more suitable for the information of free space optical communication.

【学位授予单位】：山东师范大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN24

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