Spectral Effects for an Ultrashort Pulse Train Propagating in a Two-Level Atom Medium

We investigate the spectra of a femtosecond pulse train propagating in a resonant two-level atom (TLA) medium. It is found that higher spectral components can be produced even for a 2π femtosecond pulse train. Furthermore, the spectral effects depend crucially on both the relative shift Ф and the delay time τ between the successive pulses of the femtosecond pulse train.