Focusing of WKB solution of the equation [Δ+K2n2(x)]u=0, K→∞

For a given incoming wave converging to a point, a focal solution and ray expansion for the outgoing wave are constructed. These nonuniform expansions are matched to all orders.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematichskogo Instituta im. V. A. Steklova AN SSSR, Vol. 51, pp. 123–128, 1975.The author is grateful to V. M. Babich for useful discussions during the course of the work.