Weak localization of waves

The weak localization of waves is formulated in terms of coherent multiple scattering theory. This leads, in the backscattering direction, to an enhancement of the differential cross-section. It manifests itself macroscopically by the doubling of the backscattering intensity in a narrow cone of width φ c =λ/l•θ(Ω)/τ, where θ(Ω) is the residence time around the incident direction. The corrections to transport coefficients are then derived both in two and three dimensions in terms of φ c . An e-expansion around the lower critical dimension d c =2 is then performed and leads to a wave localization threshold for d>2 around which the critical behaviour is studied. Different kinds of experimental situations leading to the observation of this backscattering cone and critical exponents are then discussed Obtention de la localisation faible des ondes a partir d'une theorie de la diffusion multiple coherente, ce qui conduit a une augmentation de la section efficace differentielle dans la direction de retrodiffusion et, macroscopiquement, a une valeur double de l'intensite retrodiffusee dans un cone tres etroit autour de la direction d'incidence (ouverture angulaire φ c ). Corrections aux coefficients de transport a 2 et 3 dimensions a partir de φ c