We study the field theoretical model of a scalar field in presence of spacial
inhomogeneities in form of one and two finite width mirrors (material slabs).
The interaction of the scalar field with the defect is described with
position-dependent mass term. Within this model we derive the interaction of
two finite width mirrors, establish the correspondence of the model to the
Lifshitz formula and construct limiting procedure to obtain finite self-energy
of a single mirror without any normalization condition.Comment: 5 pages, based on the presentation on the Ninth Conference on Quantum
Field Theory under the influence of External Conditions, Oklahoma, 200