  Background: One important ingredient for many applications of nuclear physics
to astrophysics, nuclear energy, and stockpile stewardship are cross sections
for reactions of neutrons with rare isotopes. Since direct measurements are
often not feasible, indirect methods, e.g. (d,p) reactions, should be used.}
Those (d,p) reactions may be viewed as three-body reactions and described with
Faddeev techniques.
  Purpose: Faddeev equations in momentum space have a long tradition of
utilizing separable interactions in order to arrive at sets of coupled integral
equations in one variable. While there exist several separable representations
for the nucleon-nucleon interaction, the optical potential between a neutron
(proton) and a nucleus is not readily available in separable form. The purpose
of this paper is to introduce a separable representation for complex
phenomenological optical potentials of Woods-Saxon type.
  Results: Starting from a global optical potential, a separable representation
thereof is introduced based on the Ernst-Shakin-Thaler (EST) scheme. This
scheme is generalized to non-hermitian potentials. Applications to n$+^{48}$Ca,
n$+^{132}$Sn and n$+^{208}$Pb are investigated for energies from 0 to 50 MeV
and the quality of the representation is examined.
  Conclusions: We find a good description of the on-shell t-matrix for all
systems with rank up to 5. The required rank depends inversely on the angular
momentum. The resulting separable interaction exhibits a different off-shell
behavior compared to the original potential, reducing the high momentum
contributions.

Nuclear Theory