Under the quadratic approximation of the Rytov＇s phase structure function, this paper derives the general closed-form expressions for the mean-squared width and the angular spread of partially coherent beams in turbu...Under the quadratic approximation of the Rytov＇s phase structure function, this paper derives the general closed-form expressions for the mean-squared width and the angular spread of partially coherent beams in turbulence. It finds that under a certain condition different types of partially coherent beams may have the same directionality as a fully coherent Gaussian beam in free space and also in atmospheric turbulence if the angular spread is chosen as the characteristic parameter of beam directionality. On the other hand, it shows that generally, the directionality of partially coherent beams expressed in terms of the angular spread is not consistent with that in terms of the normalized far-field average intensity distribution in free space, but the consistency can be achieved due to turbulence.展开更多
It is found that in free space, the curves of the mean-squared beam width may each have a cross point at a certain propagation distance Zc. For Gaussian array beams, the analytical expressions of zc are derived. For t...It is found that in free space, the curves of the mean-squared beam width may each have a cross point at a certain propagation distance Zc. For Gaussian array beams, the analytical expressions of zc are derived. For the coherent com- bination, Zc is larger than that for the incoherent combination. However, in non-Kolmogorov turbulence, the cross point disappears, and the Gaussian array beams will have the same directionality in terms of the angular spread. Furthermore, a short propagation distance is needed to reach the same directionality when the generalized exponent is equal to 3.108. In particular, it is shown that the condition obtained in previous studies is not necessary for laser beams to have the same directionality in turbulence, which is explained physically. On the other hand, the relative average intensity distributions at the position where the Gaussian array beams have the same mean-squared beam width are also examined.展开更多
The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation rat...The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation ratio between flange and web and flange thickness are the maior influencing factors on the spread of rolling piece, and the inclination and diameter of vertical roll together with web inner width can also influence to some extent on the spread of rolling piece.展开更多
With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere ...With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.展开更多
By using wave optics numerical simulation, the intensity-hole effect, beam spreading and wandering properties of Gaussian vortex beam propagation in atmospheric turbulence are investigated quantitatively. It is found ...By using wave optics numerical simulation, the intensity-hole effect, beam spreading and wandering properties of Gaussian vortex beam propagation in atmospheric turbulence are investigated quantitatively. It is found that an intensity hole in the center of the beam pattern appears gradually as a Gaussian vortex beam propagates. The size of the intensity hole increases with the increase of the topological charge of the vortex phase. However, the intensity hole could to some extent be filled with optical energy by atmospheric turbulence, especially in strong turbulence. The radius of the intensity hole first decreases and then increases with the growth of turbulence strength. The effective radius of vortex beam with larger topological charge is greater than with a smaller topological charge. But the topological charge has no evident influence on beam wandering.展开更多
通过数值计算斜程大气路径上传输光束的束径短期端流扩展,比较了由基于广义韦更斯-菲涅耳衍射理论导出的光束短期湍流扩展半径 Yura 理论与建立在大尺度湍涡主要产生传输光束偏折(光束抖动)和小尺度湍涡主要导致光束扩展等假设基础上的 ...通过数值计算斜程大气路径上传输光束的束径短期端流扩展,比较了由基于广义韦更斯-菲涅耳衍射理论导出的光束短期湍流扩展半径 Yura 理论与建立在大尺度湍涡主要产生传输光束偏折(光束抖动)和小尺度湍涡主要导致光束扩展等假设基础上的 Fante 光束短期湍流扩展半径理论间的差异,分析指出 Yura 理论与Fante 理论在不同传输条件下所反映出光束短期扩展的总体规律是一致的,但是在光束扩展增长的趋势、扩展半径与发射散束径间函数等关系细节上存在着较大差异.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 60778048)
文摘Under the quadratic approximation of the Rytov＇s phase structure function, this paper derives the general closed-form expressions for the mean-squared width and the angular spread of partially coherent beams in turbulence. It finds that under a certain condition different types of partially coherent beams may have the same directionality as a fully coherent Gaussian beam in free space and also in atmospheric turbulence if the angular spread is chosen as the characteristic parameter of beam directionality. On the other hand, it shows that generally, the directionality of partially coherent beams expressed in terms of the angular spread is not consistent with that in terms of the normalized far-field average intensity distribution in free space, but the consistency can be achieved due to turbulence.
基金supported by the National Natural Science Foundation of China(Grant No.61178070)the Construction Plan for Scientific Research Innovation Teams of Universities in Sichuan Province,China(Grant No.12TD008)
文摘It is found that in free space, the curves of the mean-squared beam width may each have a cross point at a certain propagation distance Zc. For Gaussian array beams, the analytical expressions of zc are derived. For the coherent com- bination, Zc is larger than that for the incoherent combination. However, in non-Kolmogorov turbulence, the cross point disappears, and the Gaussian array beams will have the same directionality in terms of the angular spread. Furthermore, a short propagation distance is needed to reach the same directionality when the generalized exponent is equal to 3.108. In particular, it is shown that the condition obtained in previous studies is not necessary for laser beams to have the same directionality in turbulence, which is explained physically. On the other hand, the relative average intensity distributions at the position where the Gaussian array beams have the same mean-squared beam width are also examined.
文摘The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation ratio between flange and web and flange thickness are the maior influencing factors on the spread of rolling piece, and the inclination and diameter of vertical roll together with web inner width can also influence to some extent on the spread of rolling piece.
文摘With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.
基金Project supported by the National Natural Science Foundation of China(Grant No.61107066)
文摘By using wave optics numerical simulation, the intensity-hole effect, beam spreading and wandering properties of Gaussian vortex beam propagation in atmospheric turbulence are investigated quantitatively. It is found that an intensity hole in the center of the beam pattern appears gradually as a Gaussian vortex beam propagates. The size of the intensity hole increases with the increase of the topological charge of the vortex phase. However, the intensity hole could to some extent be filled with optical energy by atmospheric turbulence, especially in strong turbulence. The radius of the intensity hole first decreases and then increases with the growth of turbulence strength. The effective radius of vortex beam with larger topological charge is greater than with a smaller topological charge. But the topological charge has no evident influence on beam wandering.
文摘通过数值计算斜程大气路径上传输光束的束径短期端流扩展,比较了由基于广义韦更斯-菲涅耳衍射理论导出的光束短期湍流扩展半径 Yura 理论与建立在大尺度湍涡主要产生传输光束偏折(光束抖动)和小尺度湍涡主要导致光束扩展等假设基础上的 Fante 光束短期湍流扩展半径理论间的差异,分析指出 Yura 理论与Fante 理论在不同传输条件下所反映出光束短期扩展的总体规律是一致的,但是在光束扩展增长的趋势、扩展半径与发射散束径间函数等关系细节上存在着较大差异.
基金The Natural Science Basic Research Plan in Shaanxi Province of China(Program No.2012JM8008)Scientific Research Program Funded by Shaanxi Provincial Education Department(No.14JK1350)
