Scientists at the University of Michigan say the twisted shape of the nanostructured filaments allows them to generate bright, twisted light.
Planck's law ignores, but does not prohibit, circular polarization of blackbody radiation (BBR). BBRs consisting of nanostructured filaments with twisted shapes made of nanocarbon or metal have strong ellipticity between 500 and 3000 nanometers. The submicrometer-scale chirality of these filaments meets the dimensional requirements imposed by the fluctuation dissipation theorem, which requires symmetry breaking between absorption and emissivity according to Kirchhoff's law. The resulting BBRs exhibit emission anisotropy and brightness that are 10–100 times superior to conventional chiral photon emitters. Image credit: Lu others., doi: 10.1126/science.adq4068.
“When producing twisted light using traditional methods such as electroluminescence or photon emission, it is difficult to generate sufficient brightness,” said Dr. Jun Lu, a researcher at the University of Michigan.
“We gradually realized that there is actually a very old way of producing these photons, which does not rely on the excitation of photons and electrons, but is similar to the light bulb that Edison developed. .”
“Every object that has some heat, including yourself, constantly emits photons in the spectrum associated with its temperature.”
“If an object is the same temperature as its surroundings, it will also absorb the same amount of photons. Since black absorbs all photon frequencies, this is idealized as blackbody radiation.”
Although the filament of a tungsten bulb is much warmer than its surroundings, the law that defines blackbody radiation (Planck's law) provides a good approximation of the spectrum of photons that a tungsten bulb transmits.
The photons we see as a whole look like white light, but when we pass light through a prism, we see a rainbow of different photons inside.
This radiation is also why it appears bright in thermal images, but even room-temperature objects can appear dark because they are constantly emitting and receiving blackbody photons.
Usually, the shape of the object that emits radiation is not much considered. In most cases, objects can be imagined as spheres.
However, while the shape does not affect the spectrum of different photon wavelengths, it can affect another property: polarization.
Photons from a blackbody source are typically randomly polarized, and their waves can oscillate along any axis.
New research reveals that blackbody radiation can also be twisted if the emitter is twisted on the micro or nanoscale, with the length of each twist similar to the wavelength of the emitted light.
The strength of the twist of light, or its elliptical polarization, is determined by two main factors. One is how close the wavelength of the photon is to the length of each twist, and the other is the electronic properties of the material (in this case, nanocarbon or metal).
Twisted light is also called “chiral” because the clockwise and counterclockwise rotations are mirror images of each other.
The study was done to demonstrate the premise of a more applied project that the Michigan team wants to pursue: using chiral blackbody radiation to identify objects.
They envision robots and self-driving cars that can see like a mantis shrimp, distinguishing light waves in different directions of rotation and degrees of twist.
“Advancing the physics of blackbody radiation through chiral nanostructures is at the heart of this research. Such emitters are all around us,” said Professor Nicholas Kotov of the University of Michigan.
“For example, these findings could be important in helping autonomous vehicles tell the difference between a deer and a human. Deer fur curls differently than our fabric, so even though the wavelengths are similar, Helicity emits a different light.”
The main advantage of this method of producing twisted light is its brightness, which is up to 100 times brighter than other approaches, but the light contains a wide spectrum of both wavelengths and twists.
The authors have ideas on how to address this, including exploring the possibility of building lasers that rely on twisted light-emitting structures.
They want to further explore the infrared spectrum. The peak wavelength of blackbody radiation at room temperature is approximately 10,000 nanometers or 0.01 millimeter.
“This is a noisy spectral region, but elliptical polarization could potentially enhance the contrast,” Professor Kotov says.
of the team work Published in a magazine science.
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Jun Lu others. 2024. Bright circularly polarized blackbody radiation from twisted nanocarbon filaments. science 386 (6728): 1400-1404;doi: 10.1126/science.adq406
Source: www.sci.news
