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Illustration reveals terahertz illumination (yellow curves at prime proper) getting into the brand new digicam system, the place it stimulates quantum dots inside nanoscale holes (proven as illuminated rings) to emit seen mild, which is then detected utilizing a CMOS-based chip (backside left) like these in digital cameras. Credit score: Courtesy of the researchers
The brand new terahertz digicam gadget gives larger sensitivity and velocity than earlier variations, and may very well be used for industrial inspection, airport safety, and communications.
Terahertz radiation, often known as submillimeter radiation, has wavelengths that lie between these of microwaves and visual mild. It might penetrate many nonmetallic supplies and detect signatures of sure molecules. These helpful qualities may lend themselves to a big selection of functions, together with industrial high quality management, airport safety scanning, nondestructive characterization of supplies, astrophysical observations, and wi-fi communications with larger bandwidth than present cellphone bands.
Nonetheless, designing units to detect and make photos from terahertz waves has been difficult. As such, most present terahertz units are costly, gradual, cumbersome, and require vacuum programs and very low temperatures.
Now, a brand new form of digicam that may detect terahertz pulses quickly, with excessive sensitivity, and at room temperature and stress has been developed by researchers at MIT, the University of Minnesota, and Samsung. What’s more, it can simultaneously capture information about the orientation, or “polarization,” of the waves in real-time, which existing devices cannot. This information can be used to characterize materials that have asymmetrical molecules or to determine the surface topography of materials.
The new system uses particles called quantum dots. These have recently been found to have the ability to emit visible light when stimulated by terahertz waves. The visible light can then be recorded by a device that is similar to a standard electronic camera’s detector and can even be seen with the naked eye. The device is described in a paper published on November 3 in the journal Nature Nanotechnology, by MIT doctoral student Jiaojian Shi, professor of chemistry Keith Nelson, and 12 others.
The team produced two different devices that can operate at room temperature: One uses the quantum dot’s ability to convert terahertz pulses to visible light, enabling the device to produce images of materials; the other produces images showing the polarization state of the terahertz waves.
The new “camera” consists of several layers, made with standard manufacturing techniques like those used for microchips. An array of nanoscale parallel lines of gold, separated by narrow slits, lies on the substrate; above that is a layer of the light-emitting quantum dot material; and above that is a CMOS chip used to form an image. The polarization detector, called a polarimeter, uses a similar structure, but with nanoscale ring-shaped slits, which allows it to detect the polarization of the incoming beams.
The photons of terahertz radiation have extremely low energy, Nelson explains, which makes them hard to detect. “So, what this device is doing is converting that little tiny photon energy into something visible that’s easy to detect with a regular camera,” he says. In the team’s experiments, the device was able to detect terahertz pulses at low intensity levels that surpassed the capability of today’s large and expensive systems.
The researchers demonstrated the capabilities of the detector by taking terahertz-illuminated pictures of some of the structures used in their devices, such as the nano-spaced gold lines and the ring-shaped slits used for the polarized detector, proving the sensitivity and resolution of the system.
A CMOS camera was used to capture the rotation of a terahertz beam. Credit: Courtesy of the researchers
Developing a practical terahertz camera requires a component that produces terahertz waves to illuminate a subject, and another that detects them. On the latter point, current terahertz detectors are either very slow, because they rely on detecting heat generated by the waves striking a material, and heat propagates slowly, or they use photodetectors that are relatively fast, but have very low sensitivity. In addition, until now, most approaches have required a whole array of terahertz detectors, each producing one pixel of the image. “Each one is quite expensive,” Shi says, so “once they start to make a camera, the cost of the detectors starts to scale up really, really quickly.”
While the researchers say they have cracked the terahertz pulse detection problem with their new work, the lack of good sources remains — and is being worked on by many research groups around the world. The terahertz source used in the new study is a large and cumbersome array of lasers and optical devices that cannot easily be scaled to practical applications, Nelson says, but new sources based microelectronic techniques are well under development.
“I think that’s really the rate-limiting step: Can you make the [terahertz] alerts in a facile means that isn’t costly?” he says. “However there’s no query that’s coming.”
Sang-Hyun Oh, a co-author of the paper and a McKnight Professor of Electrical and Laptop Engineering on the College of Minnesota, provides that whereas current variations of terahertz cameras price tens of 1000’s of {dollars}, the cheap nature of CMOS cameras used for this technique makes it “an enormous step ahead towards constructing a sensible terahertz digicam.” The potential for commercialization led Samsung, which makes CMOS digicam chips and quantum dot units, to collaborate on this analysis.
Conventional detectors for such wavelengths function at liquid helium temperatures (-452 levels Fahrenheit), Nelson says, which is necessary to pick out the extremely low energy of the terahertz photons from background noise. The fact that this new device can detect and produce images of these wavelengths with a conventional visible-light camera at room temperature has been unexpected to those working in the terahertz field. “People are like, ‘What?’ It’s kind of unheard of, and people get very surprised,” says Oh.
There are many avenues for further improving the sensitivity of the new camera, the researchers say, including further miniaturization of the components and ways of protecting the quantum dots. Even at the present detection levels, the device could have some potential applications, they say.
In terms of commercialization potential for the new device, Nelson says that quantum dots are now inexpensive and readily available, currently being used in consumer products such as television screens. The actual fabrication of the camera devices is more complex, he says, but is also based on existing microelectronics technology. In fact, unlike existing terahertz detectors, the entire terahertz camera chip can be manufactured using today’s standard microchip production systems, meaning that ultimately mass production of the devices should be possible and relatively inexpensive.
Already, even though the camera system is still far from commercialization, researchers at MIT have been using the new lab device when they need a quick way to detect terahertz radiation. “We don’t own one of those expensive cameras,” Nelson says, “but we have lots of these little devices. People will just stick one of these in the beam and look by eye at the visible light emission so they know when the terahertz beam is on. … People found it really handy.”
While terahertz waves could in principle be used to detect some astrophysical phenomena, those sources would be extremely weak and the new device is not able to capture such weak signals, Nelson says, although the team is working on improving its sensitivity. “The next generation lies in making everything smaller, so it will be much more sensitive,” he says.
Reference: “A room-temperature polarization-sensitive CMOS terahertz camera based on quantum-dot-enhanced terahertz-to-visible photon upconversion” by Jiaojian Shi, Daehan Yoo, Ferran Vidal-Codina, Chan-Wook Baik, Kyung-Sang Cho, Ngoc-Cuong Nguyen, Hendrik Utzat, Jinchi Han, Aaron M. Lindenberg, Vladimir Bulovic, Moungi G. Bawendi, Jaime Peraire, Sang-Hyun Oh and Keith A. Nelson, 3 November 2022, Nature Nanotechnology.
DOI: 10.1038/s41565-022-01243-9
The research team included Daehan Yoo at the University of Minnesota; Ferran Vidal-Codina, Ngoc-Cuong Nguyen, Hendrik Utzat, Jinchi Han, Vladimir Bulovic, Moungi Bawendi, and Jaime Peraire at MIT; Chan-Wook Baik and Kyung-Sang Cho at Samsung Advanced Institute of Technology; and Aaron Lindenberg at Stanford University. The work was supported by the U.S. Army Research Office through the MIT Institute for Soldier Nanotechnologies, the Samsung Global Research Outreach Program, and the Center for Energy Efficient Research Science.
