Three-dimensional confocal microscopy of colloids

Confocal microscopy is used in the study of colloidal gels, glasses, and bi nary fluids. We measure the three-dimensional positions of colloidal partic les with a precision of approximately 50 nm (a small fraction of each parti cle's radius) and with a time resolution sufficient for tracking the therma l motions of several thousand particles at once. This information allows us to characterize the structure and the dynamics of these materials in quali tatively new ways, for example, by quantifying the topology of chains and c lusters of particles as well as by measuring the spatial correlations betwe en particles with high mobilities. We describe our experimental technique a nd describe measurements that complement the results of light scattering. ( C) 2001 Optical Society of America.