Similar-shaped pulse generation in double-lambda system

This study investigates similar-shaped pulse generation in a four-level system in the double-Λ configuration. This work shows that the short pulse case can be treated as the superposition of dark-state polaritons and simultons. The propagation velocity of simulton is proportional to the intensity of probe pulses with Rabi frequencies (interacting with the ground state). The propagation velocity of polariton is proportional to more intensive coupling pulses (resonant to adjacent transitions) with equal Rabi frequencies. Simultons propagate slowly and become detached in space. Segregated polariton component acts as matched pulses. Any initial superposition evolves to distinguished simultons and a couple of similar-shaped dark-state polaritons.