- The dynamics of quantum fluctuations in an atom interacting with a standing-wave field is studied. The spectrum of resonance fluorescence is calculated using a formulation based on optical Bloch equations for two-time correlation functions and continued-fraction methods. The spectra are calculated both under resonant and nonresonant conditions. The resonance condition in the context of a standing-wave field corresponds to a velocity-tuned or Doppleron resonance that in turn depends on the intensity of the pump. The Doppleron resonances are extracted from the positions of maxima in the total intensity of fluorescence. The spectral features are explained in terms of the eigenvalues of the appropriate Floquet matrix. 1992 The American Physical Society.