Guilin Sun
Ansys Employee

There is some confusion here for the NA beam and the scalar Gaussian beam. NA bean is diffracted beam, thinking the fields at the focal plane of a microscope objective. It is Airy pattern with side lobes. It is

It is not Gaussian shape.

The simulated result suffers some discrete errors so the simulated results may not be exactly the same as theoretical value. In addition, the simulated result is full vectorial even through the excitation source has only one non-zero component. Please note that the scalar Gaussian beam is approximate, which assumes only one field component, eg, the polarization (Ex for example) in source excitation.