Phase control of squeezing in fluorescence radiation

We study squeezing properties of the fluorescence radiation emitted by a driven $\Lambda$-type atom in which the metastable lower energy levels are coupled by an additional field. We find that the relative phase of the applied fields can significantly modify the squeezing characteristics of radiation. It is shown that the additional field connecting the lower levels in the system can induce spectral squeezing in a parameter regime for which the squeezing is absent without the additional field. Moreover, the squeezing can be shifted from inner- to outer-sidebands of the spectrum by simply changing the relative phase. A dressed-state description is presented to explain these numerical results. The phase control of squeezing in the total variance of quadrature components is also examined. We show that the squeezing in total variance attains its maximal value when the system reduces to an effective two-level system.