Ph.D Student | Gero Aharon |
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Subject | Cooperative Effects in the Multiple Scattering of Photons by Atomic Gases |

Department | Department of Physics |

Supervisor | Professor Eric Akkermans |

Full Thesis text |

We study multiple scattering of photons in disordered atomic media while
taking into account cooperative effects, which originate from the interaction
between atoms through the radiation field. We show that in atomic gases
cooperative effects, like superradiance and subradiance, lead to a potential
between two atoms that decay as the inverse inter-atomic distance, where in the
case of superradiance, this potential is attractive for close enough atoms. The
contribution of superradiant pairs to multiple scattering properties of a
dilute gas, such as photon elastic mean free path and group velocity, is
significantly different from that of independent atoms. Near resonance, it
leads to a finite and positive group velocity, unlike the one obtained for
light interaction with independent atoms. We also study the photon propagation
in a gas of N atoms, using an effective Hamiltonian that accounts for photon
mediated atomic dipolar interactions. The density of photon escape rates is
obtained from the spectrum of the N x N random matrix U_{ij }= sin x_{ij}
/ x_{ij}, where x_{ij} is the dimensionless random distance
between any two atoms. A scaling function is defined to study photon escape
rates as a function of disorder and system size. Photon localization is
described using statistical properties of random networks whose mean field
solution displays a "small world" behavior.