Spacetime wave packets: New class of laser defies laws of light physics
Scientists have created a new class of laser beam that appears to violate long-held laws of light physics. These new beams, which the team calls “spacetime wave packets,” follow different rules of refraction, which could lead to new communication technologies.
Light travels at different speeds through different media, slowing down in denser materials. It’s a phenomenon that’s best summed up in a basic, middle-school science experiment: if you place a spoon in a glass of water, the spoon will appear to be broken at the water’s surface. That’s because the light is travelling slower through the water than the air, and the light rays bend as they enter the water – a phenomenon known as Snell’s Law.
But the new laser beams don’t follow this basic law of light. And it’s not just Snell’s Law either – the team says they also ignore Fermat’s Principle, which says that light always takes the shortest possible path.
“This new class of laser beams has unique properties that are not shared by common laser beams,” says Ayman Abouraddy, principal investigator of the study. “Spacetime wave packets can be arranged to behave in the usual manner, to not change speed at all, or even to anomalously speed up in denser materials. As such, these pulses of light can arrive at different points in space at the same time.”
This has some major implications for optical communications technologies. The team uses the example of a plane sending messages encoded in light to two submarines, at the same depth but different distances away. Normally, the message would arrive at the closer sub first, but with spacetime wave packets the pulses could be propagated to reach both at the exact same time.
While it may sound like this technology is contradicting some key laws of physics, the team stresses that it’s actually still in line with special relativity. That’s because they’re not messing with the oscillations of the light waves themselves – instead, they’re controlling the speeds at which the peaks of the light pulses travel. This is done using a device called a spatial light modulator, which reorganizes the energy of each pulse of light to intertwine its properties in space and time.
“Space-time refraction defies our expectations derived from Fermat’s principle and offers new opportunities for molding the flow of light and other wave phenomena,” says Basanta Bhaduri, co-author of the study.
The research was published in the journal Nature Photonics.
Source: University of Central Florida