Interference resonant propagation and spectral properties of two-colour femtosecond Gaussian pulses in three-level Λ-type atomic medium

The interference resonant propagation and spectral properties of two-colour femtosecond Gaussian pulses in three-level Λ-type atomic medium with different values of the relative phase φ is investigated by using numerical solution, which is obtained by the finite-difference timedomain (FDTD) method and the iterative predictor–corrector (PC) method for the full Maxwell–Bloch equations. It is found that, for a smaller value of the φ, the pulse splitting occurs, and when the value of the φ increases to a certain value, only the variation of pulse shape is present but the pulse splitting no longer occurs; accordingly, for the two-colour pulses with smaller areas their spectral strengths and frequency ranges decrease remarkably with the value of φ increasing; for the pulses with larger areas, with value of the φ increasing, their spectral strengths decrease evidently but the relative strengths of the higher frequency components increase significantly, while the spectral frequency range is not varied obviously. Moreover, the relative phase also has an obvious effect on population, different population evolutions can be achieved by adjusting the value of φ.