Subharmonic instabilities in resonant interactions with bichromatic fields

laser-dye molecule into account. However, the actual phys- ical mechanism responsible for the instability remains to be seen. In an attempt to develop physical intuition for the prob- lem of a nonlinear system being driven by a two-component field, we previously examined the gain for such a field driv- ing a two-level atom. 8 These calculations showed that the gain of the two-component field displays resonances when the frequency separation of the two fields is equal to the Rabi frequency or to a subharmonic of the Rabi frequency. In this paper we consider the stability of a bichromatic laser field. Since a general self-consistent solution to the multimode laser equations is not available, the stability analysis must be carried out in some other manner. The equations could be numerically integrated; however, the pa- rameter space is too large for such a solution to provide intuition. An alternative is to calculate the atomic response to the laser field and examine the gain experienced by a probe field. When the probe-field gain exceeds the laser- field gain, an instability will occur. In this paper we discuss the stability of a bichromatic field to the growth of a bichro- matic probe field by using just such an alternative.