JILA team demonstrates ‘a new way of lasing,’ a ‘superradiant’ laser

April 12, 2012 •

NIST news release



JILA/NIST physicist James Thompson, an adjoint professor of physics at CU-Boulder, says the new laser is based on a powerful engineering technique called “phased arrays” in which electromagnetic waves from a large group of identical antennas are carefully synchronized to build a combined wave with special useful features that are not possible otherwise. 

“It’s like what happens in the classical world but with quantum objects,” Thompson explains. “If you line up lots of radio antennas that each emit an oscillating electric field, you can get all their electric fields to add up to make a really good directional antenna. In the same way, the individual atoms spontaneously form something like a phased array of antennas to give you a very directional laser beam.” 


That doesn’t happen in the new JILA laser simply because the photons don’t hang around long enough. The atoms are constantly energizing and emitting synchronized photons, but on average, very few—less than one photon, in fact —stick around between the mirrors. This average, which scientists calculate indirectly based on the laser beam’s output power, is just enough to maintain an oscillating electric field to sustain the atoms’ synchronized behavior. Nearly all photons escape before they have a chance to become scrambled by the mirrors and disrupt the synchronized atoms—thus averting the very effect that causes laser frequency to wobble in a normal laser. 


“This superradiant laser is really, really dim—about a million times weaker than a laser pointer,” Thompson says. “But it is much brighter than one would expect from the ordinary uncoordinated emissions from individual atoms.” 


Despite its dim light, the extraordinary stability of the superradiant laser can be transferred by using it as part of a feedback system to "lock" a normal laser's output. The bright laser, potentially 100 to 1,000 times more stable than today’s best lasers, could then be used in the most advanced atomic clocks to induce the atomic oscillations that are the pendulum ticks of super-accurate clocks. The added stability allows for a better match to the atoms’ exact frequency, significantly boosting the precision of the clock. The improvement would extend to atomic clock-based technologies such as GPS, optical communications, advanced geodetic surveys and astronomy. 




Laura Ost, 303- 497-4880 

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