Photocount statistics in mesoscopic optics.

We report the first observation of the impact of mesoscopic fluctuations on the photocount statistics of coherent light scattered in a random medium. A Poisson photocount distribution of the incident light widens and gains additional asymmetry upon transmission through a suspension of small dielectric spheres. The effect is only appreciable when the average number n of photocounts becomes comparable or larger than the effective dimensionless conductance g of the sample.