Laser Levitates Diamonds
It’s almost a song lyric: Diamonds in the sky with with laser beams.
Nick Vamivakas, an assistant professor of optics at the University of Rochester, led an experiment in which he and his team hit a nanometer-sized piece of diamond with a laser and levitated it. On top of that, the laser made it glow green. The work was published in the journal Optics Express.
To make the diamond float, Vamivakas and his team fired a laser into a vacuum chamber, and focused the beam to a tiny point. They then sent a cloud of diamond particles into the chamber.
Laser beams — and light generally — can exert force on objects, but we don’t usually feel it because most things are so heavy the force from light doesn’t matter. But the diamonds were so tiny that they could be pushed and pulled by the laser beam. Out of the cloud of diamond particles, one was attracted to the point where the laser beam was focused, and got trapped in place. They fired a second laser at the diamond to make it glow.
The diamonds weren’t pure like the ones sold in jewelry stores. They had tiny defects, called nitrogen vacancies. Those are places where a nitrogen atom replaces the carbon atoms that make up a diamond. In a jewel that would make the diamond discolored, lowering its value. But in this case the scientists wanted the defects, because that’s what makes them light up when the second laser hits.
The diamond crystals are so tiny — 100 nanometers across on average — that their vibrations can be controlled with the laser, making the diamond a resonator. Resonators are a key part of ordinary electronics, but they’re made of solid materials. A resonator made of light could be the building block for faster computers. The diamonds’ behavior also offers insights into how tiny objects respond to friction, heat and other ordinary phenomena that change when the scale gets small enough.
The glowing diamond can also answer questions about fundamental physics. The glow happens because the second laser beam is exciting the nitrogen atom, making it release photons, a process governed by quantum mechanics. One question physicists want to answer is just how big objects can get before they lose their quantum nature.
Credit: J. Adam Fenster/University of Rochester