Net motion of an ensemble of many Brownian particles captured with a self-mixing laser

The overall dynamics of Brownian particles suspended in water were captured with high time resolution by using a self-mixing thin-slice solid-state laser. The net motion of an ensemble of many particles moving in the small imaging field observed at given time intervals was found to be represented by Brownian motions of an effective medium obeying the Ornstein-Uhlenbeck process, whose physical parameters have scaling relations with those of a real turbid medium. An approach toward measuring particle diffusion constants is described.