论文标题
关于辐射电磁场的螺旋
On the helicity of radiative electromagnetic fields
论文作者
论文摘要
得出了自由电磁场的磁性和电线的相对不变的表达，从而导致了创建这些场的电流。证明对于辐射场（例如激光脉冲），两个螺旋度均保持稳定并彼此相等。此外，螺旋性的保守性意味着在辐射电磁场中，电气和磁性矢量始终彼此正交。在量子理论中，这表明相应的量子螺旋场算子等于所有光子的旋转投影之和在其动量上。最后，例如，获得并讨论了偶极电磁脉冲场的总螺旋，光子数量和总自旋动量的表达式。
A relativistically invariant expression for the magnetic and electric helicities of free electromagnetic field through the currents, which created those field, are derived. It is demonstrated that for radiative fields (e.g. laser pulses) the both helicities are conserved and equal to each other. Moreover the conservation of the helicity means that in radiative electromagnetic fields the electric and magnetic vectors are always orthogonal to each other. Proceeding to the quantum theory, it is shown that the corresponding quantum helicity field operator is equal to the sum of projections of spins of all photons onto their momentums. Finally, as an example, the expressions for the total helicity, number of photons and the total spin momentum of the field of a dipole electromagnetic pulse are obtained and discussed.
