NON-DEGENERATE TWO-PHOTON FLUORESCENCE SPECTRUM FOR TWO-LEVEL ATOM IN SQUEEZED VACUUM
压缩真空库场中二能级原子的非简并双光子荧光谱

In this paper the master equation is derived for the atomic reduced density operator, by means of projection operator technique, starting from the Liouville equation. The nondegenerate two-photon fluorescence spectrum for an atom with two-levels in a squeezed vacuum with broad band has been studied by means of the above equation. We find that there is a new type of oscillation phenomenon, in which there are both super and lower thresholds. Between the two thresholds the atom will exhibit oscillation and the two-photon fluorescence spectrum exhibits single peak. Outside the region between the two thresholds the oscillation will not happen and the two-photon fluorescence spectrum possesses novel negative peak or peaks. The shapes of the spectra depend strongly on the natural two-photon linewidth. However, the spectra are not phase-sensitive, which is unexpected.