The rice laboratory’s discovery of the “magic nook” is based on its ultra-thin, highly oriented nanotube films

HOUSTON- (May 20, 2021) – It’s always good when your hard work reflects you well.

With the discovery of the huge polarization rotation of light, this is literally the case.

The ultra-thin, highly oriented carbon nanotube films first made a few years ago by Rice University physicist Junichiro Kono and his students turned out to be a surprising phenomenon: the ability to enable high-performance terahertz polarization rotation.

This rotation does not mean that the films are rotating. This means that polarized light from a laser or other source can now be manipulated in ways that were previously inaccessible so that it is completely visible or opaque with an extremely thin device.

The unique optical rotation occurs when linearly polarized light pulses pass the 45 nanometer film and hit the silicon surface on which it sits. The light is reflected between the substrate and the film before finally being reflected back, but with the polarization being rotated 90 degrees.

According to Kono, this only occurs when the polarization of the input light is at a certain angle to the alignment direction of the nanotubes: the “magic angle”.

The discovery of lead author Andrey Baydin, a postdoctoral fellow in Kono’s laboratory, is detailed in Optica. The phenomenon, which can be adjusted by changing the refractive index of the substrate and the film thickness, could result in robust, flexible devices that manipulate terahertz waves.

Kono said that easy-to-manufacture ultra-thin broadband polarization rotators that can withstand high temperatures will be a fundamental challenge in the design of terahertz optical devices. The bulky devices available to date allow only limited angles of polarization, so that compact devices with more power are extremely desirable.

Because terahertz radiation easily passes through materials like plastics and cardboard, they can be particularly useful in manufacturing, quality control, and process monitoring. They could also be useful in telecommunications systems and for security audits, as many materials have unique spectral signatures in the terahertz range, he said.

“The discovery opens up new possibilities for wave plates,” said Baydin. A wave plate changes the polarization of the light that moves through it. In devices such as terahertz spectrometers, which are used to analyze the molecular composition of materials, the ability to set the polarization to a full 90 degrees would allow data acquisition with a much finer resolution.

“We found that this anisotropy is near perfect especially at wavelengths in the far infrared – in other words, in the terahertz frequency range,” said Baydin. “Basically there is no attenuation in the vertical polarization and then there is significant attenuation in the parallel direction.

“We weren’t looking for it,” he said. “It was a complete surprise.”

He said the theoretical analysis showed that the effect was entirely due to the nature of the highly oriented nanotube films, which were vanishingly thin but about 2 inches in diameter. The researchers observed and confirmed this huge polarization rotation with experiments and computer models.

“Ordinarily, humans have to use millimeter-thick quartz wave plates to rotate the terahertz polarization,” said Baydin, who entered the Kono lab in late 2019 and discovered the phenomenon soon after. “But in our case the film is only nanometers thick.”

“Large and bulky wave plates are fine if you only use them in a laboratory setting, but for applications you need a compact device,” Kono said. “What Andrey found makes it possible.”

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Co-authors of the work are Rice graduates Natsumi Komatsu and Fuyang Tay as well as the alumni Saunab Ghosh, Takuma Makihara and Timothy Noe. Baydin is a postdoctoral fellow with Attwell-Welch at Rice’s Smalley Curl Institute. Kono is Karl F. Hasselmann Professor of Engineering and Professor of Electrical and Computer Technology, Physics and Astronomy as well as Material Science and Nanotechnology.

The National Science Foundation and the US Department of Energy supported the research.

Read the paper at https: //.www.osapublishing.org /optica /full text.cfm? uri =optica-8-5-760 & id =451230.

You can find this press release online at https: //.News.Rice.edu /2021 /05 /20 /Thin-Is-Now-In-Turn-Terahertz-Polarization /

Follow Rice news and media relations on Twitter @RiceUNews.

Related materials:

Nanotubes form films: http: // news.Rice.edu /2016 /04 /04 /Nanotube-line-up-to-form-films-2 /

Junichiro Kono Laboratory: http: // kono.Rice.edu

Institute for Physics and Astronomy: https: //.Physics.Rice.edu

Wiess School of Natural Sciences: https: //.Natural sciences.Rice.edu

Images to download:

https: //.Communication network.Rice.edu /News/Files /2021 /05 /0524_TERAHERTZ-1-WEB.jpg

Rice University physicists have made unique broadband polarization rotators using ultra-thin carbon nanotube films. The films optically rotate the polarized light by 90 degrees, but only if the polarization of the input light is at a certain angle to the alignment direction of the nanotubes: the “magic angle”. (Photo credit: Kono Laboratory / Rice University)

https: //.Communication network.Rice.edu /News/Files /2021 /05 /0524_TERAHERTZ-2-WEB.jpg

Ultra-thin broadband polarization rotators are made possible by ultra-thin carbon nanotube films developed at Rice University in 2016. The films made from highly aligned single-walled nanotubes were first made in 2016. (Photo credit: Kono Laboratory / Rice University)

https: //.Communication network.Rice.edu /News/Files /2021 /05 /0524_TERAHERTZ-3-WEB.jpg

SUBTITLES: Andrey Baydin. (Photo credit: Rice University)

https: //.Communication network.Rice.edu /News/Files /2021 /05 /0524_TERAHERTZ-4-WEB.jpg

SUBTITLE: Junichiro Kono. (Photo credit: Jeff Fitlow / Rice University)

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