Producing twisted light with enough brightness using traditional ways like electron or photon luminescence is quite difficult. But now, researchers at the University of Michigan have shown that it is possible to generate bright, twisted light with technology similar to an Edison light bulb.
Every object with any heat continuously sends photons in a spectrum tied to its temperature. When an object is at the same temperature as its surroundings, it absorbs the same amount of photons that it emits. This concept is known as “blackbody radiation,” where the object absorbs all photon frequencies, which is why black surfaces mainly absorb all light.
The tungsten lightbulb’s filament is much warmer than its surroundings. On the other hand, Planck’s law, which defines blackbody radiation, provides a good approximation of the spectrum of photons it sends out.
Simultaneously, the visible photons appear like white light. But under a prism, the light appears as a rainbow of different photons within it.
This radiation is why objects appear brightly in thermal images. Even at room temperature, objects constantly emit and receive blackbody photons, making them faintly visible.
While the shape of the object is often overlooked (many physics problems assume a spherical shape), it can influence a different property of the emitted radiation: polarization. Though the shape doesn’t affect the spectrum of photon wavelengths, it can alter how the photons are polarized.
Photons from a blackbody source are typically randomly polarized, meaning their waves oscillate along any axis. However, a new study discovered that if the emitter is twisted at the micro or nanoscale, with the twist length comparable to the wavelength of the emitted light, the blackbody radiation would also become twisted. The degree of bending in the light, or its elliptical polarization, depended on two factors: the relationship between the photon wavelength and the twist length and the material’s electronic properties (such as nanocarbon or metal).
Twisted light, also known as “chiral” light, has a unique characteristic: its clockwise and counterclockwise rotations are mirror images of each other. This study lays the groundwork for a future project by a Michigan team, which aims to use chiral blackbody radiation for object identification. They envision applications like robots and self-driving cars that can “see” like mantis shrimp, distinguishing between light waves with different directions and degrees of twist.
Nicholas Kotov, the Irving Langmuir Distinguished Professor of Chemical Sciences and Engineering, director of the NSF Center of Complex Particles and Particle Systems (COMPASS), and corresponding author of the study, said, “The advancements in physics of blackbody radiation by chiral nanostructures are central to this study. Such emitters are everywhere around us.”
“These findings, for example, could be important for an autonomous vehicle to tell the difference between a deer and a human, which emit light with similar wavelengths but different helicity because deer fur has a different curl from our fabric.”
The main advantage of this method for producing twisted light is its brightness, which can be up to 100 times brighter than other techniques. However, the light produced has a broad spectrum of wavelengths and twists. To address this, the team is considering ways to refine the process, such as exploring the development of a laser that uses twisted light-emitting structures.
Kotov also aims to expand the research into the infrared spectrum. At room temperature, the peak wavelength of blackbody radiation is approximately 10,000 nanometers or 0.01 millimeters.
“This is an area of the spectrum with a lot of noise, but it may be possible to enhance contrast through their elliptical polarization,” Kotov said.
Journal Reference:
- Filaments curling at the micro and nanoscale produce light waves that twirl as they travel.Jun Lu, Hong Ju Jung et al. Bright, circularly polarized blackbody radiation from twisted nanocarbon filaments. Science. DOI: 10.1126/science.adq4068