The analytical vectorial structure of a nonparaxial Gaussian beam close to the source.

The description of a nonparaxial Gaussian beam is made directly staring with the Maxwell's equations. The vector angular spectrum method is used to resolve the Maxwell's equations. As the vector angular spectrum can be decomposed into the two terms in the frequency domain, the nonparaxial Gaussian beam is also expressed as a sum of two terms. One term is the electric field transverse to the propagation axis, and the other term is the associated magnetic field transverse to the propagation axis. By means of mathematical techniques, the analytical expressions for the two terms in the source region have been derived without any approximation. The influence of the evanescent plane wave on the vectorial structure is also investigated. The results are analyzed with numerical example. This research is useful to the optical trapping and the optical manipulation.