Scientists at Houston’s Rice University have successfully increased the intensity of laser light a thousand-fold by shining it into a “nanoantenna.” At the heart of the device are two gold tips, separated by a gap measuring about a hundred-thousandth the width of a human hair. At the point where it passed through that gap, the light was “grabbed” and concentrated. Condensed matter physicist Doug Natelson believes that the technology could be useful in the development of tools for optics and chemical/biological sensing, with applications in industrial safety, defense and homeland security.
The photons in the laser light excited plasmons (oscillating electrons) in the gold tips, creating an electrical field within the gap. “At the surfaces of the metal, these fields can be very big – much bigger than those from the original radiation,” Natelson explained. “What was hard to measure was just how big.”
In order to obtain those measurements, the Rice team started by running a low-voltage, controllable current into the antenna, which caused electrons to jump across the gap. By comparing the the low-frequency electrically driven and the high-frequency optically driven currents between the tips, the researchers were able to set a standard by which the light amplification could be measured.
“The reason we're studying these enhanced fields is not just because they're there,” Natelson said. “If you can enhance the local field by a factor of 1,000, there are lots of things you can do in terms of sensors and non-linear optics. Anything that gives you a handle on what's happening at these tiny scales is very useful.”