  We continue to study the optical properties of the solar gravitational lens
(SGL). The aim is prospective applications of the SGL for imaging purposes. We
investigate the solution of Maxwell's equations for the electromagnetic (EM)
field, obtained on the background of a static gravitational field of the Sun.
We now treat the Sun as an extended body with a gravitational field that can be
described using an infinite series of gravitational multipole moments. Studying
the propagation of monochromatic EM waves in this extended solar gravitational
field, we develop a wave-optical treatment of the SGL that allows us to study
the caustics formed in an image plane in the SGL's strong interference region.
We investigate the EM field in several important regions, namely i) the area in
the inner part of the caustic and close to the optical axis, ii) the region
outside the caustic, and iii) the region in the immediate vicinity of the
caustic, especially around its cusps and folds. We show that in the first two
regions the physical behavior of the EM field may be understood using the
method of stationary phase. However, in the immediate vicinity of the caustic
the method of stationary phase is inadequate and a wave-optical treatment is
necessary. Relying on the angular eikonal method, we develop a new approach to
describe the EM field accurately in all regions, including the immediate
vicinity of the caustics and especially near the cusps and folds. The method
allows us to investigate the behavior of the EM field in this important region
that is characterized by a violent oscillatory behavior. Our results are new
and may be used to describe gravitational lensing by a large class of realistic
astrophysical lenses.
