Summary form only given. Coherent propagation of small area femtosecond pulses in a dispersive medium leads to strong coherent interactions between the driving field and the excited atoms if the relaxation times of the medium are long compared with the pulse length. As a resuit, the shape of the propagating pulse will be characteristically modified. By use of atomic Rydberg states as the dispersive medium, a systematic study of coherent pulse propagation and interference effects can be performed.
Summary form only given. Coherent propagation of small area femtosecond pulses in a dispersive medium leads to strong coherent interactions between the driving field and the excited atoms if the relaxation times of the medium are long compared with the pulse length. As a resuit, the shape of the propagating pulse will be characteristically modified. By use of atomic Rydberg states as the dispersive medium, a systematic study of coherent pulse propagation and interference effects can be performed.
Summary form only given. A small-area femtosecond pulse propagates in a dispersive medium in a coherent fashion, if the relaxation times of the medium are compared with the pulse length for a long time. As a result, the pulse will be reshaped. This has been described by linear dispersion theory. Using Rydberg states of a molecular or an atomic gas as dispersive medium, the large spectral width of the femtosecond pulse can overlap with more than one level simultaneously. In this case, the shape of the propagated pulse reflects the temporal evolution of the Rydberg wave packet formed by the resonant Rydberg states.
An investigation of the propagation properties of a short pulse in a resonant absorber with a homogeneously broadened transition is presented with two main questions in mind: 1) the influence of the input pulse area on the transitory regime and on the steady-state propagation; 2) the effects of atomic coherence on the pulse shaping and the time delay of the leading edge of the pulse. The transitory regime of a propagating pulse is investigated and the stability of some asymptotic wave form confirmed. As expected, the transversal relaxation mechanism affects critically the major features of the coherent interaction. A detailed analysis of this problem is also presented.
This thesis deals with the study of propagation effects experienced by weak light pulses as they propagate in atomic media driven by strong pulses. We explore both the ultra-short and long pulse regime and investigate the phenomena that arise at these different time scales. In the short pulse regime, a strongly driven two level atomic system presents transient light shifts, and non-adiabatic transitions occur between these adiabatic levels. We have studied a method to probe these light shifts in real time by propagating a weak probe through the medium. The light shifts enrich the spectrum of the probe and the probe gets shaped as a result. In this way a strongly driven two-level system can act as an active pulse shaper, and can introduce oscillations in the temporal profile of an ultra-short pulse at a time scale shorter than the pulse duration. We also show that by driving the system with two time delayed non-resonant strong fields, the non-adiabatic effects can be rendered phase dependent. This gives very sensitive phase control of the excited state population and can be used to formulate new techniques in interferometry. In the long pulse regime we present a new method of slowing light that can be realized in a double two-level system interacting with two orthogonally polarized light pulses that propagate along different axis. Spatio-temporal dependence of the total polarization induces a grating in the ground Zeeman coherence. The stronger of the two fields (the control field) is diffracted from this grating into the direction of the weak probe field compensating for the absorption of this latter field. A transparency window is thus created in the absorption spectrum of the probe leading to the slowing down of light. The transparency window exhibits characteristics similar to the one obtained by EIT (electromagnetic induced transparency) method. However, the important difference between our method and the traditional EIT method, is that ours doesn't rely on realizing dark state in the system. This may open the possibility of slowing down light in more complex atomic media. Moreover, when the linear absorptive response of the medium is cancelled in this manner, the nonlinear response becomes more important. In the situation where fields propagate in the same direction and have same frequency, two regimes have been investigated. For small optical depths, the effective susceptibility behaves as chi_lin exp[2 i phi] (with phi the phase difference between two fields). This renders phase control of the medium response, and the medium can be changed from an absorber to an amplifier, with normal or anomalous dispersion, by adjusting the relative phase phi. In the regime of large optical thickness, phase saturation takes place and the effective susceptibility turns into chi_lin*, changing an absorber into an amplifier without effecting the dispersive response (chi_lin is linear susceptibility).
This article presents a study of the propagation of small-area pulses of coherent light through matter. It is found that the small-area pulses exactly obey an area theorem which, in the case of an attenuating medium, requires that the pulse area decay to zero exponentially with increasing distance of propagation. This, however, does not necessarily imply that the pulse energy decays exponentially. Instead, it is found that pulses of duration comparable to or shorter than the transverse relaxation time of the medium T2 (including both homogeneous and inhomogeneous broadening) propagate with low energy loss. The results are explained in terms of simple physical arguments which indicate that the pulse envelope should oscillate between positive and negative values, causing the area to decrease without a comparable decrease in the pulse energy. Analytic solutions are presented for the case of a pulse whose envelope varies as ${t}^{k}{e}^{\ensuremath{-}t}$ for tg0, a rectangular pulse, an ultrashort pulse (i.e., pulse width much less than T2), and the leading portion of a step-function pulse. The propagation of a small-area Gaussian pulse is studied numerically.
This article presents a study of the propagation of small-area pulses of coherent light through matter. It is found that the small-area pulses exactly obey an area theorem which, in the case of an attenuating medium, requires that the pulse area decay to zero exponentially with increasing distance of propagation. This, however, does not necessarily imply that the pulse energy decays exponentially. Instead, it is found that pulses of duration comparable to or shorter than the transverse relaxation time of the medium T2 (including both homogeneous and inhomogeneous broadening) propagate with low energy loss. The results are explained in terms of simple physical arguments which indicate that the pulse envelope should oscillate between positive and negative values, causing the area to decrease without a comparable decrease in the pulse energy. Analytic solutions are presented for the case of a pulse whose envelope varies as ${t}^{k}{e}^{\ensuremath{-}t}$ for t>0, a rectangular pulse, an ultrashort pulse (i.e., pulse width much less than T2), and the leading portion of a step-function pulse. The propagation of a small-area Gaussian pulse is studied numerically.
We investigate the areas of extremely short, intense (area ⩾π) resonant optical pulses on propagation through an inhomogeneously broadened atomic medium. Experimentally, there is no apparent change in the shape of such pulses on propagation, in contradiction to the area theorem. Here we show that, although the main part of the pulse is unchanged for short propagation distances (αl∼1), it is followed by a long weak tail formed by free induction decay from the excited atoms. The tail lengthens and oscillates on propagation through the medium and permits the area theorem to be obeyed. These oscillations, which depend critically on the Doppler broadening, are reflected in the spectral analysis of the propagated pulse. We also introduce another mechanism for pulse reshaping, which is a generalization of the McCall–Hahn pulse breakup and operates at long propagation lengths (αl≫1), where the number of absorbing atoms encountered by the pulse is comparable with the number of photons in the pulse.