The problem of an atom inside a cavity in an infinite isotropic medium

The problem of a fluctuating atomic or molecular dipole inside a hollow sph erical cavity in a homogeneous, isotropic, linear but non-local medium is e xamined. The difficulty due to the infinite extension of the medium is over come by solving first, by use of an adequate basis set, the case of a mediu m limited by a concentric outer sphere of large radius (respecting the symm etry of the problem). It is then shown that when this radius tends to infin ity, the results obtained in the quasi-static approximation, and in particu lar the reflection factors involved in the response field, take definite li mits. These results, similar to but different from those obtained with a di pole outside a filled sphere, give a rigorous background to further extend the efficient 'propagator method' to the case of atomic or molecular system s confined in hollow cavities, or bubbles of finite thickness, of a micro- or nanometer size. (C) 1999 Elsevier Science B.V. All rights reserved.