Representation of the pressure field of an extended source as a geometric-optical series in the two-dimensional case

The asymptotical solution of two-dimensional nonuniform Helmholtz' equation in space with a variable refraction index is considered. Volumetric density of a source is different from zero in a finite region. It is shown that this asymptotical solution can be represented as a geometric-optical series. The algorithms for calculation of all characteristics of this series are given.