Scattering of light by a quantum harmonic oscillator

A study is made of the scattering of light by a quantum harmonic oscillator with the emission of a single photon. The second-quantization representation is adopted for both the incident and the emitted field. The unperturbed Hamiltonian of the quantum oscillator in a monochromatic field can be diagonalized; this corresponds to the existence of stationary states of the system consisting of the oscillator and the quantized monochromatic electromagnetic field. The concept of coherent states is introduced for such a system. The scattering of light i s considered by perturbation theory for the emitted field.