Velocity-selective resonance dips in the probe absorption spectra of Rb   D2 transitions induced by a pump laser
  We report experimental observation of velocity-selective resonances in the Doppler-broadened probe absorption spectra of 85Rb and 87Rb D2 transitions in the presence of a strong copropagating pump laser locked to a frequency within the Doppler profile of the transition. The set of three dips having the separation of allowed hyperfine transitions can be moved along the Doppler profile by tuning the pump laser frequency indicating a resonance between the pump laser frequency and the velocity shifted probe laser frequency. 
S.Chakrabarti, A.Pradhan, A.Bandyopadhyay, A.Ray, B.Ray, N.Kar and   P.N.Ghosh