The topic of this work deals with theoretical and experimental studyof the control of ultrashort pulse coherent propagation in opticallydense medium. First, we describe the basics of propagationphenomena. The optical thickness characterizes the importance of thetemporal distortion of the pulse profile. As prisms or gratingscompressors are used to cancel the dispersion of transparent medium,we show that a high resolution pulse shaper can compensate for theresonant dispersion. Secondly, we study the idea of using a strongdriving pulse, to control the transient properties of a weakresonant pulse simultaneously propagating in the medium. The strongfield induces transient modifications in the medium, that modify viaradiation the electric field of the weak resonant propagating pulse.In a three level ladder system, modulations appear on the intensityprofile, and reveal the light shift induced (off resonance) on thetwo upper levels. Their characteristic duration is shorter than theinitial pulse duration : new components thus appear on thetransmitted spectrum. These oscillations are the consequence of thebeating between the incident and the radiated field whose frequencysweeps in time, following the light shift. In the bichromaticexcitation of a two level system, two spatial configurations giveaccess to different information. Besides the previous phenomenaappearing in non collinear geometry, the non adiabatic transitionsinduced by the driving field are also involved in collinearinteraction. A weak pulse can be used as a very sensitive probe tothese effects. Finally, we study a configuration where twoorthogonally polarized pulses, excite resonantly a four level systemdegenerated two by two. With the strong field mixing the states, theemission and absorption path of the weak field have similarcontribution. The two paths interfere thus modulating thetransmitted pulse energy. The interplay of the light shift and theinterference, enables us to control the gain and the pulse temporalshape as well.
