Theory of fluorescence and probe absorption in the presence of a driving field using semiclassical dressed states

A theory of resonance fluorescence in a monochromatic field and pump-probe spectroscopy is developed using semiclassical dressed states. The semiclassical dressed states are obtained via a rotation from the time-dependent state vectors in a field-interaction representation. Although the semiclassical dressed states are not stationary states as are the dressed states in a quantized-field formulation, they still offer all the conceptual advantages of a dressed-atom approach. Moreover, the line-shape formulas can be obtained directly from physically intuitive equations, without having to invoke the quantum regression theorem and without having to worry about cascades and coherences in the ladder of quantized dressed states.