In our system, a colloidal particle (upper left (a), red) is trapped by optical tweezers (upper left (b)) as a surrounding colloidal suspension flows past. Surprisingly, long range order develops in the particle density (lower left, dark bands are regions with over-representation of particles, sigma is the particle diameter). A novel analysis of particle motions using a technique from computer science reveals the otherwise hidden flow patterns in the fluid surrounding the probe (right). This is a research collaboration between the research groups of Aaron Dinner, Norbert Scherer and Stuart Rice.
