Quantum Electrodynamics

This chapter discusses the photonic applications, beginning with the elementary processes of single-photon absorption, and stimulated and spontaneous emission, and computation of Einstein A and B coefficients. It presents two-photon processes-absorption and emission of light, both from different and identical beams, as well as linear scattering of light both elastic and inelastic varieties. The chapter also presents intermolecular forces modified by external radiation. In order to treat molecular vibrational Raman scattering, it is advantageous to invoke the Born-Oppenheimer approximation and separate the electronic and nuclear degrees of freedom. The van der Waals dispersion potential has been recalculated using a number of differing physical viewpoints within the framework of molecular quantum electrodynamics (QED) in the multipolar coupling scheme. These include response theory, and coupling of induced multipole moments as well as simplification of the computation via introduction and employment of an effective two-photon interaction Hamiltonian.