Ph.D Student | Ofer Firstenberg |
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Subject | Spatial Phenomena and Atomic Motion in Electromagnetically Induced Transparency Medium |

Department | Department of Physics |

Supervisors | Professor Emeritus Ron Amiram |

Full Professor Nir Davidson | |

Full Thesis text |

The quantum optics phenomenon of electromagnetically induced transparency (EIT) occurs when two radiation fields excite two atomic levels to a common upper level, creating a coherent superposition that reduces the absorption of the medium. In this thesis, we study the effects of the thermal motion in an EIT medium of hot atomic vapor, focusing mainly on the diffusion of the complex atomic coherence. From the spectral viewpoint, we investigate the mechanisms of Doppler broadening, Dicke narrowing, and Ramsey narrowing, which determine the transmission line-shape and the accompanied refraction. From the spatial viewpoint, we study the transverse dynamics of the light-matter polariton that slowly traverses the EIT medium and the dynamics of stored light. We utilize the technique of light storage to examine the diffusion of images imprinted onto the coherence field and demonstrate an interference behavior for patterns with a non-uniform phase. The self-similar solutions of complex diffusion are determined and experimentally exemplified. An important outcome of Dicke narrowing is the quadratic dependence of the absorption and refraction line-shapes on the wave-vectors difference between the probe and the pump. It follows that the complex susceptibility for a given resonance condition depends on the spatial frequencies of the light fields. This dependency results in a diffusion-like and a diffraction-like behavior of slowly propagating light packets, with the ratio between the induced diffusion and the induced diffraction determined by the group velocity. Naturally, slow light is also subjected to the regular (free-space) optical diffraction throughout its propagation. By carefully tuning the parameters of the system, the induced diffraction can be set to counteract the regular diffraction, thus completely eliminating the diffraction in the medium. Here, diffraction is suppressed for an arbitrary paraxial image and for any distance along the propagation direction, since it is manipulated in its natural spatial-frequency basis rather than in real space. By further introducing an angle between the pump and the optical axis, the induced diffraction is biased, inflicting a directional drift on the probe envelope. Finally, the interaction may be increased and the induced diffraction doubled, so that the overall optical diffraction is exactly reversed. This creates a medium which undoes diffraction that has already taken place and which acts similarly to a negative-index lens that focuses light which has already diverged. All the aforementioned manipulations of diffraction are experimentally demonstrated and quantitatively explained.