3-LEVEL ATOM IN A SQUEEZED VACUUM .1. THE POPULATIONS

We consider a three-level atom in any of its possible configurations, ladder, lambda or vee, which interacts with two classical, resonant, m onochromatic electromagnetic fields. We suppose the levels \0>, \1> an d \2> to be unequally spaced, so that one field strongly couples only the 0-1 transition, and another field only the 1-2 transition. In addi tion, the atom is interacting with two squeezed fields, one centred on each of the two transition frequencies. The effects of collisions, as an example of a conventional dissipative process, are also included. We develop a unified description of the properties of the three-level system (as far as possible independent of the particular configuration ) which is based upon an exact rate equation/diagrammatic approach. In this paper we show that the atomic populations are strongly affected by the squeezing phases, the degree of squeezing and the intensities o f the applied fields, in addition to the collisions. In a subsequent p aper we shall consider resonance fluorescence in the same system.