The theory of electromagnetism swallowed up the theory of light.

磁电学说取代了光学论.

Based on the classical theory of electromagnetism, the relation and the difference between OAM and the parameter of the beam in paraxial approximation are analyzed.

从经典电磁场理论出发，主要介绍了傍轴近似条件下，光束的轨道角动量和光束的参数之间的关系。