When atoms in a crystal are struck by laser light, their electrons, excited by the light, typically begin moving back and forth together in a regular pattern, resembling nanoscale soldiers marching in a lockstep formation.
But according to a new theory developed by Johns Hopkins researchers, under the right conditions these atoms will rebel against uniformity. Their electrons will begin moving apart and then joining together again repeatedly like lively swing partners on a dance floor.
Moreover, the researchers say, this atomic freestyle dancing can be controlled, paving the way for tiny computer components that emit less heat and new sensors to detect bio-hazards and medical conditions.
"By choosing particular atoms in the proper configuration and directing the right laser light at them, we could control the behavior of these 'nano-dancers,'" said Alexander E. Kaplan, a professor in the Department of Electrical and Computer Engineering in Johns Hopkins' Whiting School of Engineering. "The essential thing is, these are completely designable atomic structures."
Kaplan and Sergei N. Volkov, a postdoctoral fellow in his lab, described this phenomenon in a paper published recently in the journal Physical Review Letters . The next step is for other researchers to conduct lab experiments in an effort to validate the theory and predictions advanced by Kaplan and Volkov.
Kaplan, an internationally renowned nonlinear optics expert who studies how matter interacts with strong light, said his and Volkov's "nano-riot" idea runs counter to a widely accepted concept. For decades, Kaplan said, scientists have adhered to the Lorentz-Lorenz theory, which asserts that the atomic electrons in a crystal, exposed to a laser beam, will move back and forth in tandem in a uniform way under any conditions.
"But we've concluded that under certain circumstances, the nearest atoms will behave much differently," he said. "Their electrons will move violently apart and come back together again, staging a sort of 'nano-riot.'"
For this to happen, Kaplan said, several critical conditions must exist. First, the system must be very small, typically involving no more than a few hundred atoms, and the atoms must be arranged in a one-dimensional or two-dimensional configuration. The atoms must be grouped in a sufficiently close concentration; interestingly, though, this arrangement may allow more space between atoms than exists in a typical crystal. Also, the frequency of the laser driving the atoms must be closely tuned to one of the specific frequencies of the atomic electrons -- the so-called atomic resonance -- in the way that a radio receiver might be tuned to a particular station.
When these critical conditions are met, the interacting excited atomic electrons get strongly "coupled," and their motion is affected by one another. The atomic dance partners begin to match or counter-match the motion of each other, while still being driven by the laser's "music."