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| Credit: Technology Review |
Today, Darran Milne and Natalia Korolkova at the University of St Andrews in Scotland outline another idea. These guys have worked out how to make an optical invisibility cloak that you can turn on and off.
What makes this possible is a process known as electromagnetically induced transparency--a phenomenon in which certain materials become transparent when zapped by light from two carefully tuned lasers.
This works for materials with atoms that can exist in three different electronic states--say a, b and, the highest, c. The idea here is that the first laser beam is absorbed by the material because it excites electrons from state a to state c. The second laser is also absorbed because it excites electrons from state b to state c.
If the frequencies of the lasers are close together, they can be tuned in a way that makes them interfere destructively. And when this happens, their ability to excite electrons cancels out.
When this happens, the laser photons suddenly pass through the material unimpeded, sometimes at dramatically reduced at speeds (which is how experiments that stop light are performed).
What makes this possible is a process known as electromagnetically induced transparency--a phenomenon in which certain materials become transparent when zapped by light from two carefully tuned lasers.
This works for materials with atoms that can exist in three different electronic states--say a, b and, the highest, c. The idea here is that the first laser beam is absorbed by the material because it excites electrons from state a to state c. The second laser is also absorbed because it excites electrons from state b to state c.
If the frequencies of the lasers are close together, they can be tuned in a way that makes them interfere destructively. And when this happens, their ability to excite electrons cancels out.
When this happens, the laser photons suddenly pass through the material unimpeded, sometimes at dramatically reduced at speeds (which is how experiments that stop light are performed).
Technology Review: An Invisibility Cloak With An On-Off Switch
Physics arXiv: Electromatically induced invisibility cloaking
Physics arXiv: Electromatically induced invisibility cloaking
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