Laser beam divergence was considered using the components of the Poynting vector. A physical interpretation of the real and imaginary parts of the “longitudinal” field component (along the $z$ axis, the direction of beam propagation) is given in an exponential representation. The longitudinal field component was shown to be the reason for the formation of laser beam divergence. This fact was used to reveal fundamental differences between Laguerre–Gaussian beams and incoherent rays in the focal region. The possibility of using selective action on the longitudinal field component to decrease the divergence of Laguerre–Gaussian beams is discussed.

中文翻译：

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Poynting矢量和光束发散

使用Poynting向量的分量考虑了激光束发散。对“纵向”场分量的实部和虚部（沿$ z $轴，光束传播方向）的物理解释以指数表示。纵向场分量被证明是形成激光束发散的原因。这个事实被用来揭示拉盖尔-高斯光束与焦点区域内非相干光线之间的根本差异。讨论了对纵向场分量采用选择性作用以减小拉盖尔－高斯光束发散的可能性。