Microspheres, photonic atoms and the physics of nothing

The transfer of energy between neighboring molecules plays a pivotal role in nature. In photosynthesis, for example, a plant fuels its metabolism and growth with sunlight by taking advantage of a curious physical phenomenon that allows energy to hop from one chlorophyll molecule to another situated about a half a nonometer away. A couple of hundred chlorophyll molecules pass the energy they collect from the sum in this way to a single reaction center, the starting point for subsequent chemical reactions. Without this mechanism for transfering energy between molecules, photosynthesis would largely cease, and we would likely starve. About 15 years ago I began to wonder whether similar forms of energy transfer could influence photochemistry within aerosol particles. In particular, I wanted to know whether there are subtleties in the way energy is conveyed between molecules in an isolated droplet about 10 micrometers in diameter. To most physicists, the idea must have seemed crazy. After all, the range of the longest substantial exchange of this sort, as Nobelist Jean Perrin had discovered and Theodore Förster had described in quantummechanical terms decades ago, is only about 5 nonometers. The vessels I was proposing to use would be 2,000 times larger. So there was no obvious reason to expect that their tiny size would have any influence at all. Still, research elsewhere with similar microscopic particles hinted of interesting physical effects, and I urged one of my graduate students, Lorcan Folan, to investigate. Little did I know that the results we and other were soon to obtain would distinguish the lowly aerosol particle as a high-tech item. Such microscopic particles now stand poised to serve in a variety of ways, from lasers of exceptional efficiency to optical filters of unprecedented purity and chemical probes of tiny size-to name just few obvious applications.But before delving into how tiny spheres can provided such valuable functions, it is worthwhile to review how this rapidly evolving creature of 21st-century technology first arose from a primordial soup of basic research.