The Electromagnetically Induced Transparency of Quasi-A-type Four-level Atom System at Low Light Levels

The probe gain and the population in high level in the Quasi-A-type four-level atom system interacting with two fields at low light levels are investigated in this paper： The system always displays three gain peaks with probe detuning. At the same time, the electromagnetically induced transparency （EIT） can be observed in two windows which only relate to coupling detuning. When the system displays EIT, the population in the high level is zero. If the phase of the probe field is changed, the probe gain would be changed and absorption occurs but the population in the high level is a constant. It is worth noting that all results are got on the condition that the fields are as weak as the spontaneous emission fields and without any approximation.

The Electromagnetically Induced Transparency of Quasi-A-type Four-level Atom System at Low Light Levels

We investigate the spontaneous emission decay of a two-level atom embedded in a structure with modified density of spectrum. The decay rate of the atom is calculated by integrating the dynamic equation numerically. It is found that the decay in the early stage is sensitively relay on the spectrum function. It is quit different from that in the Weisskopf-Wigner approximation.