  We study the 2-D Helmholtz equation in perturbed stratified media, allowing
the existence of guided waves. Our assumptions on the perturbing and source
terms are not too restrictive.
  We prove two results. Firstly, we introduce a Sommerfeld-Rellich radiation
condition and prove the uniqueness of the solution for the studied equation.
Then, by careful asymptotic estimates, we prove the existence of a bounded
solution satisfying our radiation condition.
