Energy Transfer Between Radiation and Atomic Transitions

Daniel F. Walls, Gerard J Milburn

Andreas F. Molisch, Bernhard P Oehry

Abstract Since the beginning of this century we have a rough understanding about the structure of atoms. They consist of a nucleus and electrons orbiting around this nucleus. We know that electrons occupy only certain discrete energy states. When they decay from a high-energy state to a low-energy state, they emit electromagnetic radiation. Usually, the low-energy state will be the ground state. In that case, the emitted radiation is called resonance radiation.1 Since the resonance photons have an energy that corresponds to the energy of the transition, they can easily be absorbed by other ground-state atoms. A ground-state atom that absorbs the resonance photon is excited to the upper state for some time and will eventually release the photon again. This absorption/reemission process can be repeated many times, until the photon finally escapes from the vapour. This process is called ‘radiation trapping’ (also known as ‘imprisonment of resonance radiation’, ‘radiative transfer of spectral lines’, ‘line transfer’, or ‘radiation diffusion’).

Daniel F. Walls, Gerard J Milburn

N. A. Enaki

The symmetry of the two types of resonances between the spontaneous and induced emissions by two- and single-photon transitions of three inverted radiators from the ensemble is studied. The condition for increasing the collective decay rate of the entangled photon pairs generated by the system relative to the dipole-forbidden transition is found. One of them corresponds to the situation when the total energy of emitted photons by two dipole-active radiators enters the two-photon resonance with the dipole-forbidden transitions of the third atom. The second effect corresponds to the scattering situation when the differences of the excited energies of two dipole-active radiators are in resonance with the dipole-forbidden transitions of the third atom. It is shown that transfer of the excited energy between two quantum oscillators off resonance takes place through a dipole-forbidden transition of the thread atom.

Mitchel Weissbluth

Vlasta Horvatić, Mladen Movre, Cedomil Vadla

The cross sections for the excitation energy transfer induced by collisions with He, Ar and Na ground-state atoms have been measured. The sodium atoms in the 4D state have been produced by two-photon excitation using cw laser radiation at 578.89 nm. Within a model which takes into account collisional population and depopulation of the 4F level as well as radiative relaxation (direct or cascade) of the 3D, 4P, 4D and 4F states ending in the 3P level, the rate for the collisional transfer turns out to be related to the ratio of the steady-state populations created in 3D and 4D states. They have been determined by measuring the fluorescence intensities of the and transitions. The measurements yield the following cross section values for those processes investigated: , and , at .