Phase-dependent spectra in a driven two-level atom
  We propose a method to observe phase-dependent spectra in resonance fluorescence, employing a two-level atom driven by a strong coherent field and a weak, amplitude-fluctuating field. The spectra are similar to those which occur in a squeezed vacuum, but avoid the problem of achieving squeezing over a $4\pi $ solid angle. The system shows other interesting features, such as pronounced gain without population inversion. 
Peng Zhou and S. Swain