Coherent emission in time-separated fields

Experimental observations are reported of coherent emission from an absorbing rarefied gas following the interaction with two standing-wave pulses separated by a time T. The emission occurred at a time 2T after the first pulse and was associated with the spatial transport of polarization and the formation of spatial polarization harmonics because of a phase jump following two-photon interaction with the field of the second pulse. The formation of spatial polarization harmonics was responsible for the appearance of Ramsey resonances in the optical region. Intensity oscillations were observed at the center of the absorption line on tuning the frequency of the exciting laser and varying the delay time between the pulses.