Spontaneous Raman Scattering

In this chapter, we extend the Hamiltonian governing the interaction between light and molecules to incorporate external reservoirs, including the free space modes reservoir, the dephasing reservoir associated with spectral line broadening in gases, and the reservoir responsible for vibron mode relaxation. These reservoirs are essential for facilitating light emission by atoms. We demonstrate that, under the conditions of weak interaction between the reservoirs and the atom, and when the reservoirs are in thermal equilibrium, it is possible to eliminate the reservoirs’ variables from the operator equations describing the atom-vibron system. As a result, the system exhibits noise terms, leading to a set of complex equations. To tackle these intricate equations, we develop a perturbation theory, enabling us to solve them systematically. We establish that the Raman effect emerges as a consequence of the second-order perturbation within this framework, ultimately allowing us to determine the Raman spectrum.