Twisted carbon nanotube filaments can emit circularly polarized thermal radiation with a high brightness

Amazing stuff!

"... Usually photons from a blackbody source are randomly polarized—their waves may oscillate along any axis. The new study revealed that if the emitter was twisted at the micro or nanoscale, with the length of each twist similar to the wavelength of the emitted light, the blackbody radiation would be twisted too.  The strength of the twisting in the light, or its elliptical polarization, depended on two main factors: how close the wavelength of the photon was to the length of each twist and the electronic properties of the material—nanocarbon or metal, in this case. 

Twisted light is also called “chiral” because the clockwise and counterclockwise rotations are mirror images of one another. The study was undertaken to demonstrate the premise of a more applied project that the Michigan team would like to pursue: using chiral blackbody radiation to identify objects. ...

While brightness is the main advantage of this method for producing twisted light, up to 100 times brighter than other approaches, the light includes a broad spectrum of both wavelengths and twists. ... a laser that relies on twisted light-emitting structures. ..."

From the perspective abstract:

"Every object, including the human body, emits thermal radiation that is generated by tiny internal fluctuating dipoles. These heat waves can oscillate with some degree of preferential direction, called polarization.

Among different types of polarization (linear, circular, or elliptical), circular polarization of thermal radiation is desired for advanced technologies, such as thermal imaging, biological sensing, and passive infrared detectors for security systems. However, heat waves emitted by most objects exhibit only a small degree of circular polarization.

The rare effect of circularly polarized thermal radiation was primarily observed in astronomical objects (1). On page 1400 of this issue, Lu et al. (2) report that twisted carbon nanotube filaments can emit circularly polarized thermal radiation with a high brightness. These materials could be used at high temperatures that are unattainable by existing emitters."

From the editor's summary and abstract:

"Editor’s summary

Upon heating, carbon nanotube yarns or tungsten wires mechanically twisted to have submicrometer-scale chirality can generate circularly polarized light ranging from the visible to mid-infrared wavelengths. Lu et al. found that unlike other chiral emitters, these blackbody emitters have no vibronic state limitations and can achieve high brightness ... The spectral characteristics were modeled with a mechanism that reconciled Planck’s law and the fluctuation-dissipation theorem. Ceramic composites allowed the electrically heated emitters to achieve long lifetimes. ...

Abstract

Planck’s law ignores but does not prohibit black-body radiation (BBR) from being circularly polarized. BBR from nanostructured filaments with twisted geometry from nanocarbon or metal has strong ellipticity from 500 to 3000 nanometers. The submicrometer-scale chirality of these filaments satisfies the dimensionality requirements imposed by fluctuation-dissipation theorem and requires symmetry breaking in absorptivity and emissivity according to Kirchhoff’s law. The resulting BBR shows emission anisotropy and brightness exceeding those of conventional chiral photon emitters by factors of 10 to 100. The helical structure of these filaments enables precise spectral tuning of the chiral emission, which can be modeled using electromagnetic principles and chirality metrics. Encapsulating nanocarbon filaments in refractive ceramics produces highly efficient, adjustable, and durable chiral emitters capable of functioning at extreme temperatures previously considered unattainable."

Twisted light: The Edison bulb has purpose again

Twisted Edison: bright, elliptically polarized incandescent light (original news release)

Thermal radiation with a twist (no public access) "Carbon nanotube filaments with a twisted geometry emit spinning heat waves at high temperatures"

Bright, circularly polarized black-body radiation from twisted nanocarbon filaments (no public access)

Behind the bulb, a screen displays the temperature of the glowing filament. The wavelengths of light emitted by the filament depend on its temperature, and how well the filament twirls the light depends on how close the wavelengths are to the pitch of the filament’s twists.