CASIMIR EFFECT IN ABSORBING MEDIA

The Casimir force between two dielectric slabs of finite thickness is calculated for the case of dissipative media. The medium is modeled as a continuous field of quantum harmonic oscillators interacting with the heat bath. The electromagnetic field inside and outside the cavity formed by the plates is found for the ground state of the coupled system, and its pressure is calculated. Two terms in the expression for the Casimir force are distinguished. One is the electromagnetic vacuum pressure, which is the only contribution in the case of lossless media. The other arises from the Langevin forces that appear together with the damping as the result of the interaction of atoms with the heat bath. It is shown that both contributions are necessary in order to arrive at a finite result.