Transformation of optical speckles by atomic vapors: From Rayleigh to Weibull intensity statistics

We investigate the transformation of Rayleigh speckle patterns by an atomic cesium vapor. After propagation through the atomic vapor, the incident exponentially decaying intensity distribution of the Rayleigh speckles is transformed with enhancement of high intensities probabilities (extreme events). The measured intensity distributions are fitted by Weibull distributions. The nonlinear interaction between the atomic vapor and the optical field leads to intensity-dependent refraction and absorption, resulting in changes of the speckle spots' intensities with propagation. We measure the inverse of the shape parameter of the Weibull distributions as a function of laser detuning and interpret the results by modeling the speckle propagation.