大气湍流像差散焦和像散与高斯涡旋光束焦面光强

分别研究了构成大气湍流波像差中的散焦和像散两个低阶像差对高斯涡旋激光束传输和成像的影响.采用菲涅耳-基尔霍夫衍射积分理论和大气湍流波相位结构函数的平方近似研究了聚焦高斯涡旋光束在大气湍流中散焦和像散影响下焦面光强的分布特性.导出了斜程传输条件下接收面上平均光强分布的积分表达式,并采用数值模拟方法研究湍流强度、传输距离和拓扑电荷对焦面光强的调制规律.结果表明:在弱湍流起伏区域,散焦和像散两类像差对高斯涡旋光束的光强分布影响都很小,可以忽略;在中等湍流区域,随着光束传输距离和湍流强度的增加,两类像差都导致高斯涡旋光束的光强峰值降低、束径扩展、中心暗斑扩大.当单拓扑电荷高斯涡旋光束传输时,在同等传输条件下,像散导致的光强峰值降低比散焦更严重,主亮斑区域外的次级亮环强度更大,光斑和中心暗斑扩展更明显.与单拓扑电荷光束相比较,散焦和像散导致双拓扑电荷光束的扩展更加明显,中心光斑更大,亮环区域外的次级亮环更明显;但是,由于光的相干性的降低和光束的偏折效应,像散导致光束中心的暗斑变为次级亮斑.

Defocus and astigmatic aberration of the turbulent atmosphere and the intensity distribution of a vortex carrying Gaussian beam

The effects of defocus and astigmatism aberration of the turbulent atmosphere on the intensity distribution of a focused vortex carrying Gaussian beam are investigated. The integral expression of the intensity distribution on the focal plane in slant path is derived from the extended Fresnel-Kirchhoff diffraction integral and the quadratic approximation of phase structure function. And the influences of the three factors, turbulent strength, the propagation distance and the topological charge of the initial beam, are investigated by numerical calculation. Our results show that in weak turbulent region, the effects of defocus and astigmatism aberration in turbulent atmosphere on the intensity distribution of a vortex carrying Gaussian beam are very small and can be ignored. However, in the middle turbulent region, the effects of defocus and astigmatism are pronounced. As the propagation distance and the turbulent strength increase, both aberrations cause the decrease of the intensity peak value, the spreading of the beam, and the stretching of the dark core. For the beams with single topological charge, under the influence of astigmatism, the peak value of the intensity decreases more seriously, the intensity of the secondary maximum stripe increases much faster, and the focal spot expands more than the effect of defocus aberration. Compared with single topological charge, the effects of defocus and astigmatism of vortex beam with double topological charge are more obvious. The focal spots are expanded, and the secondary maximum stripes are more obvious. However, under the effect of astigmatism, because of the reduction of the coherence and the deflection effect of the beam, the dark core on the focal plane tends to break into two dark regions separated by a bright region.