A Princeton-led team of researchers has discovered an entirely new mechanism for making common electronic materials emit laser beams.
The finding could lead to lasers that operate more efficiently and at higher temperatures than existing devices, and find applications in environmental monitoring, homeland security, medical diagnostics and other areas that require extremely sensitive detection of different chemicals.
"This discovery provides a new insight into the physics of lasers," said Claire Gmachl, who led the study. Gmachl, an electrical engineer, is the director of the Mid-Infrared Technologies for Health and the Environment (MIRTHE) Centre.
The phenomenon was discovered in a type of device called quantum cascade laser, in which an electric current flowing through a specially designed material produces a laser beam.
Gmachl's group discovered that a quantum cascade laser they had built generated a second beam with very unusual properties, including the need for less electrical power than the conventional beam.
"If we can turn off the conventional beam, we will end up with a better laser, which makes more efficient use of electrical power," said Gmachl.
The team that conducted the study includes Gmachl's graduate student Kale Franz, who built the laser that revealed the new phenomenon, and Stefan Menzel, a graduate student from the University of Sheffield, who unearthed the unique properties of the phenomenon during an internship at Princeton University last summer. The study was published online in Nature Photonics.
Light is made up of particles called photons. Common sources of light emit photons that are in a random order, like crowds milling about a busy marketplace.
In contrast, photons in a laser are "in sync" with one another, like a military band marching in formation. This property, called coherence, allows laser light to shine in an intense, narrow beam of a single, very pure colour.
The new laser has some interesting features. For instance, in a conventional laser relying on low momentum electrons, electrons often reabsorb the emitted photons, and this reduces overall efficiency.
In the new type of laser, however, this absorption is reduced by 90 percent, said Franz. This could potentially allow the device to run at lower currents, and also makes it less vulnerable to temperature changes. "It should let us dramatically improve laser performance," he said.