啁啾脉冲高斯光束在大气湍流中的传输特性

基于广义惠更斯-菲涅耳原理,推导出啁啾脉冲高斯光束在湍流大气中传输的光谱解析表达式,并对解析表达式进行了数值仿真。结果表明：啁啾参数越大,光源谱宽越宽;当光源相对谱宽大于0.336时,轴上点光谱产生蓝移;湍流使得轴上点光谱的相对频移量减小,相对频移量随源光谱宽的增大而非线性增大;增大光束束腰半径可减小湍流对光谱频移、光束展宽的影响。     

贝塞尔高斯涡旋光束在大气湍流中的传输特性

基于广义惠更斯-菲涅耳原理,推导了贝塞尔高斯涡旋光束在湍流大气中传输时系统平均光强的解析表达式,研究了贝塞尔高斯空心涡旋光束在湍流大气中的光强传输特性,同时分析了大气湍流的强弱、涡旋光束的拓扑荷等对光束质量的影响.结果表明:贝塞尔高斯涡旋光束在大气湍流中传输时,光强分布经历几个连续的变化,相位奇异性也会在传输过程中消失,该过程与涡旋光束拓扑荷的数目、光束的束腰宽度以及大气湍流的强弱等因素密切相关.拓扑荷数目高的涡旋光束在湍流大气中传输时,其奇异性的保持较拓扑荷数目低的涡旋光束要好.另外,基于桶中功率理论,分析研究了涡旋光束的拓扑荷数目、大气湍流强弱和束腰宽度对贝塞尔高斯涡旋光束在大气湍流中传输时的光束质量的影响.     

贝塞尔高斯涡旋光束在大气湍流中的传输特性

为了探测更高轨道的空间目标,研制了一台通光口径为Ф750 mm的望远镜.该望远镜为主焦点光学系统,由一片二次非球面反射元件和四片透射元件组成,具有大视场(4°),大相对孔径(1∶1.32)和宽光谱(500~800 nm)的特点.本文以该望远镜的研制为基础,介绍了其光学系统各个元件的单独检测和系统装调完成后的整体检测方法和过程.采用样板法对系统中的球面透射元件进行了单独检测,采用透射无像差补偿器法对二次非球面反射镜进行了单独检测,采用反射无像差补偿器法对组合起来的透射校正镜组进行了检测,并且对系统装调对准之后的光学系统进行室内平行光管和室外对星观测两种方法进行检测.测量结果均满足设计要求,其中球面透镜的面形误差小于0.1个光圈,反射元件和透射元件非球面表面的面形误差均优于λ/30(λ=632.8 nm),透射校正镜组的波像差优于λ/30(λ=632.8nm).光学系统整体检测结果表明,室内和室外检测结果一致,其像面的80% 能量集中度直径在4°的全视场范围内均小于2个像元,达到了设计的成像要求.     

啁啾高斯脉冲通过增益色散介质的传输特性

采用复数波数定义和衍射积分方法,研究了啁啾高斯脉冲在增益色散介质中的传输特性,给出了介质增益谱为洛仑兹分布时的频谱分布以及时空分布的传输解析公式,详细分析了传输过程中光场的频谱和时空分布、脉宽和频谱变化以及谱移等特性。结果表明,啁啾高斯光束在介质中传输时其时间波形仍保持高斯分布不变,但在传输过程中其脉宽会发生变化。在传输过程中,啁啾参量会影响谱宽的减小程度以及谱移的幅度。啁啾参量越大,脉宽展宽和谱宽压窄的效果越明显,同时,随着传输距离的增大,光谱谱移也越明显。对于给定的啁啾参量,随着传输距离的增大,谱移将最终趋于一恒定值。     

环状光束在大气湍流中的传输特性

基于广义惠更斯-菲涅耳原理,利用Rytov近似理论,推导出环状光束在湍流大气介质中光强分布的解析表达式。在此基础上,根据强度二阶矩定义,推导出环状光束在大气湍流中传输的M2因子的表达式。最后,详细讨论了环状光束在湍流介质中的传输变换特性及其光束质量变化。研究结果表明,环状光束在湍流介质中传输时,湍流的强弱直接影响着环状光束传输变换的程度和快慢。由于湍流的影响,环状光束在传输过程中由完全相干光变成部分相干光。环状光束在湍流中传输的M2因子与光束遮拦比、湍流强度、光束波长以及传输距离有关。选择合适的光束遮拦比和波长等光束参数,可以有效地控制激光束在湍流介质中传输的光束质量。     

相干合成光束在湍流大气中的传输

分析了湍流大气对相干合成光束传输的影响,根据广义惠更斯-菲涅耳原理,对相干合成光束在不同强度湍流大气中传输进行计算,对接收平面处的光强分布的统计特性,如桶中功率(PIB)曲线、局部功率曲线进行比较.研究结果表明,较弱的湍流大气对相干合成光束的传输影响较小,接收平面的光强分布以及PIB曲线基本不变;随着湍流强度的增大,相干合成光束的光强分布和PIB曲线产生显著变化,光斑扩展和能量的弥散速度加快,光束的能量集中度显著降低.计算了湍流大气传输后光束的空间相干度,认为空间相干度下降是降低相干合成效果的原因,对如何降低湍流大气的影响进行讨论.     

平顶光束通过湍流大气传输的光谱特性

采用Rytov相位结构函数二次近似的方法,推导出了平顶光束在湍流大气中的光谱传输方程,详细研究了其光谱特性,并给出了合理的物理解释。研究表明,轴上点光谱为蓝移,随着离轴距离的增大,光谱由蓝移逐渐变为红移,轴外点存在多阶光谱跃变现象。随着湍流的增强,光谱位移量和光谱跃变量减小、光谱跃变现象消失。特别分析了平顶光束与高斯谢尔模型(GSM)光束通过湍流大气传输的光谱跃变之间存在的差异。     

啁啾脉冲的光谱整形

为了获得更高功率的输出激光脉冲,需要将注入到主放大链的种子脉冲进行光谱整形来补偿放大过程中的增益窄化效应.利用展宽器中啁啾脉冲的光谱具有空间排布的特点.采用石英晶体平凸透镜空间光强度调制器间接地实现窄带激光脉冲的光谱整形,在展宽器的输出端获得了光谱呈平顶分布的种子啁啾脉冲.通过调节偏振片的透偏方向,可方便地调谐输山脉冲光谱的形状.     

高斯涡旋光束在大气湍流传输中的特性研究

为了研究大气湍流对高斯涡旋光束传递信息的影响,理论分析了经过大气湍流的高斯涡旋光束轨道角动量(OAM)模式的径向平均功率和归一化平均功率分布、固有模式指数、初始光束半径和湍流强度;采用纯相位扰动逼近的有效性,数值模拟高斯涡旋光束在传输中的OAM模式径向平均功率分布的变化。建立传输模型并进行外场激光大气传输实验,对比分析了模拟和实测的OAM归一化平均功率分布,结果表明在弱湍流条件下,OAM模式的径向平均功率随着接收器孔径尺寸的增加而变化,逐渐趋于稳定值。对于一般常用的接收孔径,在强湍流或较小的初始光束半径条件下对OAM模式干扰十分严重。验证了用数值方法模拟OAM在湍流介质中的模式变化过程的可靠性。     

Changes in the spectrum of Gaussian Schell-model beams propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the spectrum of Gaussian Schell-model (GSM) beams propagating through turbulent atmosphere is derived analytically. It is shown that, if the scaling law is valid, the normalized spectrum S(ω) of GSM beams propagating through turbulent atmosphere is the same as the normalized source spectrum S⁽⁰⁾(ω), whether GSM source is quasi-homogenous or not. On the other hand, if the scaling law fails, S(ω) of GSM is different from S⁽⁰⁾(ω). The structure constant of the refractive index, transverse coordinate of observation point and spatial correlation length of the source affect the spectrum, which is illustrated numerically.     

Spectral changes of aberrated stochastic electromagnetic flat-topped beams propagating in turbulent atmosphere

In this paper, taking the electromagnetic partially coherent flat-topped (PCFT) beam as an example, we investigate the spectral changes of stochastic electromagnetic beams with astigmatic aberration propagating through a turbulent atmosphere. The analytic expressions for the spectrum of the beams propagating through the turbulent atmosphere are derived. It is shown that the spectral changes of the electromagnetic PCFT beams in the turbulent atmosphere are closely related with the astigmatism aberration, the strength of atmospheric turbulence, the inner scale of turbulence, the correlation of source and the order of flatness of electromagnetic PCFT beams. It is important to note that the spectral changes of the aberrant electromagnetic PCFT beams are insensitive to the atmospheric turbulence. Some possible explanations have also been given for the interesting physical phenomena.     

Changes in the spectrum of twist anisotropic Gaussian Schell-model beams propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the spectrum of twist anisotropic Gaussian Schell-model (TAGSM) beams propagating through turbulent atmosphere is derived analytically by using the partially coherent complex curvature tensor. The relative spectral shift of TAGSM beams propagating through turbulent atmosphere is closely related with the strength of atmospheric turbulence, the beam’s parameter and the radial coordinate. The on-axis spectral shift of TAGSM beams propagating through turbulent atmosphere changes from blue shift to red shift with the increasing of the propagation distance z, and at a certain propagation distance z, there exists a rapid transition of the spectrum at the critical position r_c.     

Changes in the coherence of quasi-monochromatic electromagnetic Gaussian Schell-model beams propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the mutual coherence function of quasi-monochromatic electromagnetic Gaussian Schell-model (EGSM) beams propagating through turbulent atmosphere is derived analytically. By employing the lateral and the longitudinal coherence length of EGSM beams to characterize the spatial and the temporal coherence of the beams, the behavior of changes in the spatial and the temporal coherence of those beams is studied. The results show that with a fixed set of beam parameters and under particular atmospheric turbulence model, the lateral coherence of an EGSM beam reaches its maximum value as the beam propagates a certain distance in the turbulent atmosphere, then it begins degrading and keeps decreasing along with the further distance. However, the longitudinal coherence length of an EGSM beam keeps unchanging in this propagation. Lastly, a qualitative explanation is given to these results.     

Spectral shifts and spectral switches of elliptical Gaussian beam propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the spectrum of elliptical Gaussian beam (EGB) propagating through turbulent atmosphere can be derived analytically by tensor method. It can avoid time-consuming numerical integral that was commonly used in the previous study of spectral changes. Analytical results show that the on-axis normalized spectrum S(ω) of EGB propagating through turbulent atmosphere is different from the original spectrum S₀(ω) and there exist spectral shifts and spectral switches for EGB propagating through turbulent atmosphere. Besides, spectral shifts and spectral switches of EGB are closely related with the structure constant of the turbulent atmosphere, the beam parameters and the coordinate of observation point. Compared with the Gaussian beam, there are two spectral switches for EGB propagating through turbulent atmosphere.     

拉盖尔-高斯光束在湍流大气中的螺旋谱特性

研究了拉盖尔-高斯光束在湍流大气中的传输特性.在利托夫近似下,得到接收孔径处光束的螺旋谱的积分表达式.通过数值仿真得出大气湍流对光束螺旋谱的影响以及光束螺旋谱随各参数值的变化特性.仿真发现大气湍流会使螺旋谱发生弥散.而且随着拓扑荷,接收孔径半径,折射率结构函数及距离的增加,螺旋谱弥散加剧.经拟合得到描述螺旋谱弥散程度的无量纲方差V随距离成6次函数关系;与接收孔径半径及折射率结构函数成二项式关系;而与拓扑荷呈11次多项式关系.最后得出径向指数,束腰半径对螺旋谱的影响非常小,并且根据此结论推出光 关键词： 拉盖尔-高斯光束 大气湍流 螺旋谱 无量纲方差     

Spectral properties of apertured stochastic electromagnetic twist anisotropic Gaussian Schell-model beam propagating in turbulent atmosphere

Based on the extended Huygens-Fresnel principle, analytical formulas are derived for the cross-spectral density matrix of an apertured stochastic electromagnetic twist anisotropic Gaussian Schell-model (ETAGSM) beam propagating in a turbulent atmosphere by use of a tensor method. Spectral properties of apertured ETAGSM beam are closely related with the strength of atmospheric turbulence, the aperture widths and the beam's parameters, etc. Our main attention was focused on the influence of the aperture widths, atmospheric turbulence, twist parameters and partial coherence on the spectral properties (including spectral degree of polarization, the spectral degree of coherence and the spectral density) of apertured ETAGSM beam propagating in turbulent atmosphere. Numerical calculation results and analysis are given.     

湍流大气中斜程传输光场的相位特性

运用功率谱反演法对斜程传输大气湍流扰动相位屏进行了数值模拟。通过建立激光束初始畸变相位模型,从波前峰谷值和波前功率谱密度函数两个方面,对激光束通过大气湍流后的相位特性进行了研究,重点分析了湍流传输距离和天顶角对激光束波前相位分布的影响。研究结果表明:激光束在湍流大气斜程传输后,其波前相位会发生明显畸变,且空间高频相位较低频相位所占比例明显增加;通过湍流后的波前相位与传输距离及天顶角密切相关,传输距离越长,天顶角越大,相位畸变程度越大,高频相位所占比例越多。     

湍流大气中斜程传输光场的相位特性

运用功率谱反演法对斜程传输大气湍流扰动相位屏进行了数值模拟。通过建立激光束初始畸变相位模型,从波前峰谷值和波前功率谱密度函数两个方面,对激光束通过大气湍流后的相位特性进行了研究,重点分析了湍流传输距离和天顶角对激光束波前相位分布的影响。研究结果表明：激光束在湍流大气斜程传输后,其波前相位会发生明显畸变,且空间高频相位较低频相位所占比例明显增加;通过湍流后的波前相位与传输距离及天顶角密切相关,传输距离越长,天顶角越大,相位畸变程度越大,高频相位所占比例越多。