Abstract: Influence of relative phase between probe and driving fields(Φ) Oil propagation effect of a Doppler broadened quasi-Λ type four-level atomic system with spontaneously generated coherence(SGC) is numerically studied.It is shown that by choosingΦ, we can obtain greater GWI and longer propagation distance where GWI exists and hence obtain higher LWI intensity.Doppler broadening width and propagation directions of probe and driving fields have considerable effect on phase·dependent spatial evolutions of GWI and LWI intensity.

Key words: four-level system, propagation effect, relative phase, Doppler broadening, lasing without inversion