压缩真空库场中二能级原子的非简并双光子荧光谱

NON DEGENERATE TWO PHOTON FLUORESCENCESPECTRUM FOR TWO LEVEL ATOM INSQUEEZED VACUUM

利用投影算符技巧从刘维方程出发导出了二能级原子约化密度算符主方程，研究了压缩真空库场中二能级原子的非简并双光子荧光谱特性．发现与真空库或热库中双光子荧光不同，在非简并双光子情况中存在一种新型振荡现象，它具有上下两个阈值，在上下阈值之间原子发生振荡，在两阈值之外原子将不发生振荡．在两阈值之间原子的非简并双光子荧光谱呈现正峰结构，在两阈值之外双光子荧光谱具有负的峰结构．光谱形状强烈地依赖于双光子自然线宽，但光谱是非相敏性的。

Abstract 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.