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 co-propagating 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 move along the Doppler profile while the pump laser frequency is tuned. This indicates a resonance between the pump laser frequency and the velocity shifted probe laser frequency.