Abstract: We investigate effect of atomic densities (N) on propagation and spectral property of femtosecond Gaussian pulses in a three-level Λ-type atomic medium by using numerical solution of full Maxwell-Bloch equations.It is shown that,for pulses with smaller area 2π,propagate in mediums with different N,pulse splitting does not occur and strength of spectral component near central frequency decreases considerably as N increases.For pulses with area 4π,pulse splitting could occur when pulses propagate in dilute medium with greater atomic density and in dense medium,and pulse spectral bandwidth and strength of spectral component with higher frequency increase with increasing of N in dilute medium.Spectrum broadening in dense medium is much smaller than that in dilute medium with greater atomic density.For pulses with larger area 8π,pulse splitting is similar to that of 4π pulses.Pulse spectral bandwidth and strength of spectral component with higher frequency increase monotonously with increasing of N.And spectrum broadening in dense medium is much larger than that in dilute medium with smaller atomic density.

Key words: femtosecond Gaussian pulse, atomic density, propagation, spectrum