Laser-Linewidth Effects on the Photon-Phonon Conversion Rate at a Gas-Solid Interfaces

摘要

An atom, bounded to the surface of a crystal, absorbs photons from a strong incident laser field and subsequently emits phonons into the solid. This paper studies the influence of the laser linewidth of this photon phonon conversion process. The appearance of coherences obscures the interpretation of the equation of motion in terms of transition rates and prohibits the derivation of a master equation in the transient region. The absorbed energy from the driving field, which is assumed to be resonant with a set of two levels only, results from the work done by the external field on the transition dipole. In the steady state, the energy absorption from the radiation field equals the energy emission in the phonon field. It is shown that in this long time limit the coherences can be expressed in terms of the populations, and hence the system is again described by a master equation. Specific aspects of the finite laser bandwidth are pointed out.