Ever since two centuries ago, researchers learned that, when heated, materials generate light in a predictable pattern of wavelengths. A new study depicts a material that produces light when heated that seems to exceed the limits set by the natural law. The research has been published in the journal Nature Scientific Reports today, on March 23rd.
Back in 1900, Max Planck first mathematically explained a spectrum of radiation and entered in the quantum age with the suspicion that energy can only exist in distinct values. Similar to the fireplace poker that looks red hot, raising the heat cause all materials to produce more intense radiation, with the climax of the emitted pattern switching to longer wavelengths as heat increases.
Planck’s Law is not Violated
In respecting Planck’s Law, nothing can generate more radiation than a theoretical object that absorbs energy perfectly, a so-called ‘blackbody.’ The new material found by Shawn Yu Lin, lead author of the research and professor of physics at Rensselaer Polytechnic Institute, breaks the limits of Planck’s Law, as it generates a consistent light similar to that emitted by lasers or LEDs, but with no expensive structure needed to generate the stimulated emission of those technologies.
Besides the spectroscopy study, Lin previously published imaging research in IEEE Photonics Journal. Both describe an increase in radiation at approximately 1.7 microns, which is the near-infrared portion of the electromagnetic spectrum.
“These two papers offer the most convincing evidence of ‘super-Planckian’ radiation in the far-field,” said Lin. “This doesn’t violate Planck’s law. It’s a new way to generate thermal emission, a new underlying principle. This material, and the method that it represents, opens a new path to realize super-intense, tunable LED-like infrared emitters for thermophotovoltaics and efficient energy applications.”
For this study, Lin created a 3D tungsten photonic crystal, a material that can manage the properties of a photon, in a pattern similar to that of a diamond crystal, and covered with an optical cavity that refines the light.
The Results Cannot Be Fully Explained
Lin has striven to develop this advance for 17 years since he designed the first all-metallic photonic crystal in 2002, and the two studies portray the most stringent tests he has performed.
“Experimentally, this is very solid, and as an experimentalist, I stand by my data. From a theoretical perspective, no one yet has a theory to fully explain my discovery,” Lin said.
In both pieces of research, Lin put his sample and a blackbody control side by side on a single section of silicon substrate, removing the option of changes between testing the sample and control that could affect the results.
The sample and control were then heated in a vacuum chamber to 600 degrees Kelvin (620 degrees Fahrenheit). In one of the studies, Lin depicts the spectral analysis performed in five positions as the opening of an infrared spectrometer moves from a view full of the blackbody to one of the material. The maximum emission, with an intensity of eight times more powerful than the blackbody sample, takes place at 1.7 micrometers.
The other research presented images captured with a near-infrared conventional charge-coupled device, a camera that can snap the expected radiation discharge of the material. Even though theory doesn’t fully explain the impact, Lin believes that the balances between the sheets of photonic crystal enable light to show up from within the numerous spaces inside the crystal. The generated light bounces back and forth within the limits of the crystal structure, which changes the property of the light as it moves to the surface to get to the optical cavity.
“We believe the light is coming from within the crystal, but there are so many planes within the structure, so many surfaces acting as oscillators, so much excitation, that it behaves almost like an artificial laser material,” Lin said. “It’s just not a conventional surface.”