Universal conductance fluctuations of light

We observed that laser light, multiply scattered through small samples of o ptically dense colloidal suspensions, builds up anomalous long range correl ations in the transmission speckle pattern. The dynamic autocorrelation fun ction of angular integrated light intensity has two contributions, C-2(t) a nd C-3(t). which decay on very different time scales. C-2 and C-3 are expla ined by onefold and twofold crossing, respectively, of multiple scattering paths, in quantitative agreement with theory. Our C-3 data provide the firs t evidence for the classical wave analog of universal electronic conductanc e fluctuations and pinpoint their physical origin as a macroscopic quantum- wave interference effect.