November 18, 2008 feature
Can a single molecule behave as a mirror?
(麻豆淫院Org.com) -- 鈥淲e have shown for the first time, theoretically, that a single molecule can behave as a perfect mirror,鈥� Mario Agio tells 麻豆淫院Org.com. 鈥淚magine that your mirror at home becomes a single molecule and that you put a strong lens between you and it. Well, you could still see the image of your face reflected鈥A]mazing if you think that a molecule is just about a nanometer in size.鈥�
Agio is a scientist at the Nano-Optics Group headed by Vahid Sandoghdar at ETH Zurich, Switzerland. Sandoghdar鈥檚 team investigates both theoretically and experimentally how light interacts with nanoscale objects. 鈥淭heoretically,鈥� Agio says, 鈥渨e show that a directional dipole wave can be reflected by one point-like oscillating dipole.鈥� The results of the work done by the Group, including Gert Zumofen and Nassiredin Mojarad, can be seen in 麻豆淫院ical Review Letters: 鈥淧erfect Reflection of Light by an Oscillating Dipole.鈥�
鈥淭here are many possibilities for this kind of work,鈥� Agio points out. He explains that, 鈥淥nce you can realize efficient coupling between a photon and a molecule or atom in free space, there is a great deal that you can do. For example, advanced solar cells, spectroscopy, quantum communications and quantum computation would all benefit from stronger interaction between light and matter.鈥�
However, there are some technical problems that need to be overcome in the lab. One of the more pressing issues is the fact that molecules behave like strongly damped oscillators at room temperature. 鈥淲e need to cool the system to very low temperatures,鈥� Agio says. Referring to work published earlier this year in Nature 麻豆淫院ics (鈥淓fficient coupling of photons to a single molecule and the observation of its resonance fluorescence鈥�), he continues: 鈥淚ndeed, our experiments have been able to achieve 12 percent extinction of light in the forward direction by a single molecule.
Agio also explains that there are problems with being able to focus. 鈥淭he reflection is only 100 percent if you can create a focused beam with lenses that just are not available today. But a terrific 80 percent reflection should be possible even with today鈥檚 conventional lenses and laser beams.鈥�
Sandoghdar鈥檚 group has been considering future developments for this work, and Agio discusses some of the possibilities. 鈥淲e are considering the use of optical antennas to overcome the limitations of focusing. We should be able to channel and collect light more efficiently, improving the coupling between a photon and a single molecule, very much in the same way the antenna in your cell phone receives and send calls.鈥� He pauses before adding: 鈥淲e鈥檇 have to make it very small, though, scaling everything down to optical frequencies is challenging.鈥�
Agio is optimistic. He points out that the group has already done some work along the lines of optical antennas, and that it, too, has been reported in 麻豆淫院ical Review Letters. 鈥淲e have already shown experimentally that noble metal nanoparticles are very efficient optical antennas for single molecules,鈥� he says, referencing an article titled, 鈥淓nhancement of single molecule fluorescence using a gold nanoparticle as an optical nano-antenna.鈥�
鈥淣ow,鈥� he continues, describing the next steps, 鈥渨e are working on how to combine the focusing with the antenna to make all of this workable.鈥�
More Information:
G. Zumofen, N. M. Mojarad, V. Sandoghdar, and M. Agio. 鈥淧erfect Reflection of Light by an Oscillating Dipole,鈥� 麻豆淫院ical Review Letters (2008). Available online: .
G. Wrigge, I. Gerhardt, J. Hwang, G. Zumofen & V. Sandoghdar. 鈥淓fficient coupling of photons to a single molecule and the observation of its resonance fluorescence,鈥� Nature 麻豆淫院ics (2008). Available online: .
Sergei K眉hn, Ulf H氓kanson, Lavinia Rogobete, and Vahid Sandoghdar. 鈥淓nhancement of Single-Molecule Fluorescence Using a Gold Nanoparticle as an Optical Nanoantenna,鈥� 麻豆淫院ical Review Letters (2006). Available online: .
Copyright 2007 麻豆淫院Org.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of 麻豆淫院Org.com