We present a realistic theoretical treatment of a three-level Λ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. We take into account a dynamic rate of influx of atoms in the two lower levels of the Λ, and an outflux from all the three levels. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. Our predictions are in excellent agreement with the reported experimental results for 4He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.
We present a realistic theoretical treatment of a three-level Λ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. We take into account a dynamic rate of influx of atoms in the two lower levels of the Λ, and an outflux from all the three levels. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. Our predictions are in excellent agreement with the reported experimental results for 4He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.
We present a detailed theoretical treatment of a three-level $\ensuremath{\Lambda}$ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions (VCCs) are modeled in the strong-collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the $\ensuremath{\Lambda}$, are in excellent agreement with the reported experimental results for ${^{4}\text{H}\text{e}}^{\ensuremath{\ast}}$. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.
We have experimentally studied electromagnetically induced transparency (EIT) and absorption (EIA) in hot 85Rb atomic vapor using probe and coupling light with comparable power levels. We have shown that strong-probe EIT has different linewidth and appears in fewer configurations than does usual, weak probe EIT. In V-scheme, where optical pumping and saturation are dominant mechanisms, narrow EIT is possible only when a probe is tuned to a closed transition. The width of the EIT resonance increases with laser intensity with non-linear dependence, similar to the weak-probe EIT in Lambda- scheme. The EIT in Lambda- scheme was observed when two transitions had balanced population losses. The EIA was modified for the case of a strong probe as well: in four-level N-scheme with Zeeman sublevels the EIA was observed only for a cycling transition when F'=F+1, where F and F' are the angular momenta of the 5 2S1/2 (ground) and 5 2P3/2 (excited) state hyper-fine levels, respectively. The combination of strong probe and strong coupling laser beam intensities allows observation of an absorption dip due to three-photon resonance in a four-level scheme that involves the Raman transitions via virtual level.
In this thesis we study light-matter coherence phenomena related to the interaction of a coherent laser field and the so-called Λ-system, a three-level quantum system (e.g., an atom). We observe electromagnetically induced transparency (EIT), slow and stored light in hot rubidium vapor. For example, a 6 μs Gaussian pulse propagate at a velocity of ~1 km/s (to be compared with the normal velocity of 300 000 km/s). Dynamic changes of the control parameter allows us to slow down a pulse to a complete stop, store it for ~100 μs, and then release it. During the storage time, and also during the release process, some properties of the light pulse can be changed, e.g., frequency chirping of the pulse is obtained by means of Zeeman shifting the energy levels of the Λ-system. If, bichromatic continuous light fields are applied we observe overtone generation in the beating signal, and a narrow `dip' in overtone generation efficiency on two-photon resonance, narrower than the `coherent population trapping' transparency. The observed light-matter coherence phenomena are explained theoretically from first principles, using the Lindblad master equation, in conjunction with the Maxwell's equations. Furthermore, we analyze an optical delay-line based on EIT and show that there is in principle (besides decoherence) no fundamental limitation, but the usefulness today is scant. The combination of EIT and a photonic crystal cavity is inquired into, and we show that the quality value of a small resonator (area of 2.5λ×2.5λ with a missing central rod) can be enhanced by a factor of 500 due to the increased modal density close to two-photon resonance. Open system effects (decoherence effects) are thoroughly investigated using a coherence vector formalism, furthermore, a vector form of the Lindblad equation is derived. Specifically we find an open system channel that lead to slow light and gain.
We report a likely observation of cw lasing without inversion in a gas of hot rubidium atoms in an optical cavity under conditions of electromagnetically induced transparency (EIT). The medium is pumped coherently and resonantly by a single ``coupling'' beam which also produces EIT in the lasing transition. The steady-state intensity exhibits thresholds as a function of the atomic density and the strength of the coupling beam. A theoretical model for an effective three-level lambda system indicates that gain without inversion is possible in this system if the two ground states are coupled by depolarizing collisions, and if the decay branching ratios meet certain conditions.
We experimentally and theoretically analyze the propagation of weak-signal field pulses under the conditions of electromagnetically induced transparency (EIT) in hot Rb vapor, and study the effects of resonant four-wave mixing (FWM). In particular, we demonstrate that in a double-Λ system, formed by the strong control field with the weak resonant signal and a far-detuned Stokes field, both continuous-wave spectra and pulse propagation dynamics for the signal field depend strongly on the amplitude of the seeded Stokes field, and the effect is enhanced in optically dense atomic medium. We also show that the theory describing the coupled propagation of the signal and Stokes fields is in good agreement with the experimental observations.
Electromagnetically induced transparency (EIT) has mainly been modelled for three-level systems. In particular, a considerable interest has been dedicated to the Lambda-configuration, with two ground states and one excited state. However, in the alkali-metal atoms, which are commonly used, hyperfine interaction in the excited state introduces several levels which simultaneously participate in the scattering process. When the Doppler broadening is comparable with the hyperfine splitting in the upper state, the three-level Lambda model does not reproduce the experimental results. Here we theoretically investigate the EIT in a hot vapor of alkali-metal atoms and demonstrate that it can be strongly reduced due to the presence of multiple excited levels. Given this model, we also show that a well-designed optical pumping enables to significantly recover the transparency.