Quasisimultons in thermal atomic vapors.

The propagation of two-color laser fields through optically thick atomic ensembles is studied. We demonstrate how the interaction between these two fields spawns the formation of copropagating, two-color solitonlike pulses akin to the simultons found by Konopnicki and Eberly [Phys. Rev. A 24, 2567 (1981)]. For the particular case of thermal Rb atoms exposed to a combination of a weak cw laser field resonant on the D1 transition and a strong sub-ns laser pulse resonant on the D2 transition, simulton formation is initiated by an interplay between the 5s1=2 − 5p1=2 and 5s1=2 − 5p3=2 coherences. The interplay amplifies the D1 field at the arrival of the D2 pulse, producing a sech-squared pulse with a length of less than 10 μm. This amplification is demonstrated in a time-resolved measurement of the light transmitted through a thin thermal cell. We find good agreement between experiment and a model that includes the hyperfine structure of the relevant levels. With the addition of Rydberg dressing, quasisimultons may offer interesting prospects for strong photon-photon interactions in a robust environment