Diffraction of electromagnetic waves by an extended gravitational lens

We continue our study of the optical properties solar gravitational lens (SGL). Taking next step beyond representing it as an idealized monopole, we now characterize field Sun using infinite series multipole moments. consider propagation electromagnetic (EM) waves in this within first post-Newtonian approximation general theory relativity. The problem is formulated Mie diffraction theory. solve Maxwell's equations for EM wave propagating background a static extended gravitating body, while accounting contributions. Using wave-theoretical approach and eikonal approximation, find exact closed form solution Debye potentials determine at image plane strong interference region lens. resulting characterized by new integral. show how presence multipoles affects lens, distinct patterns. identify deflection angle with individual contributions due to each multipoles. Treating extended, axisymmetric, rotating that zonal harmonics causes light diffract into area whose boundary caustic particular shape. appearance caustics modifies point-spread function (PSF) thus affecting its properties. allows lensing realistic possesses arbitrary number This {\em angular method} represents improved treatment lensing. It may be used wave-optical description many astrophysical lenses.