Abstract

Work on deterministic instabilities and chaos over the past decade has largely focused on spatiotemporal behavior. In connection with fluids and, more recently, laser dynamics, spatial structures have played an increasingly important role. In this work we show that standing light waves, which can exert periodic radiation forces on dielectric particles, can be used to produce complex structures in colloidal crystals of polystyrene spheres. The crystals are formed by a strong repulsive Debye-potential interaction in ultraclean aqueous environments having particle densities on the order of 1014/cmA Quasielastic laser-light scattering measurements show that the crystals assume a face-centered cubic lattice with a (111) plane separation of several thousand angstroms. The injection of a standing optical wave produces a second periodic potential, which in one-dimensional results in the well-studied circle mapping for the position of the nth ball: Xn + 1 = Xn + a + sin 2kxn, where a is the unperturbed lattice spacing and is proportional to light intensity. We have studied the phenomenon in two-dimensional and three-dimensional systems and will show that the light forces available from cw lasers can produce "chaotic crystals," as well as other solutions, for certain winding numbers and intensities.

© 1990 Optical Society of America