Now, researchers from MIT, the University of Minnesota, and Samsung have developed a new type of camera (Terahertz cameras at low cost) that can detect terahertz pulses quickly, with high sensitivity, at room temperature and pressure. In addition, it can capture information about the direction or “polarization” of the waves directly, which existing devices cannot. This information can be used to describe materials with asymmetric molecules or to determine the surface properties of materials.
The new technique uses so-called quantum dots which, recently discovered, can emit visible light when stimulated by terahertz waves. Visible light can be registered by a device similar to a standard electronic camera detector and can be seen with the naked eye. The device is described in a paper published yesterday in the journal Nature Nanotechnology, by MIT doctoral student Jiaojian Shi, chemistry professor Keith Nelson and 12 others.
The team developed two different devices of (a Terahertz cameras at low cost) that one can operate at room temperature: and another that uses the ability of a quantum dot to convert terahertz pulses into visible light, allowing the device to create images of something; the other creates an image showing the polarization state of the terahertz waves.
The new camera is multi-stage, made using a standard manufacturing process similar to that used for microchips. A network of parallel nanoscale gold lines, separated by narrow slits, depends on the substrate; On top is a layer of light-emitting quantum dots; and above is the CMOS chip used to create the image. A polarization detector, called a polarimeter, uses a similar technique, and uses a nanoscale ring-shaped ring, which allows it to detect the polarization of incoming light.
Photons from terahertz radiation have very low energy, Nelson explains, which makes them difficult to detect. “So what this device does is convert that small amount of 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 levels that are beyond the capabilities of today’s large, expensive systems.
The researchers demonstrated the detector’s capabilities by taking terahertz images with light of some of the materials used in their device, such as the nano gold lines with holes and ring-shaped slits used for the polarized detector. , shows the sensitivity and resolution of the system.
Building a practical terahertz camera requires equipment that generates terahertz waves to illuminate subjects, and something else to detect them. In this last case, the current terahertz detectors are slow, because they are based on the detection of the heat produced by the waves, and the heat spreads slowly, or they use fast photodetectors, but of low sensitivity. Also, until now, most methods required multiple terahertz detectors, each producing one pixel of the image. “Each one is expensive,” Shi says, “so when they start making cameras, the cost of detectors starts to go up very quickly.”
Although the researchers say that they have solved the problem of finding terahertz pulses with their new work, there is still no good source – and it is something that many researchers around the world are working on. The terahertz sources used in the new study are large lasers and optics that cannot be easily replicated in practical applications, Nelson says, but new microelectronic systems are being developed from these sources.
“I think that’s really a bit of a breakthrough: can you create [terahertz] signals easily and cheaply?” he says. “But it’s sure to come.”
Sang-Hyun Oh, the author of the paper and the McKnight Professor of Electrical and Computer Engineering at the University of Minnesota, adds that although the current type of terahertz camera costs tens of thousands of dollars, the cheap nature of the camera CMOS is used for this purpose. The system makes it a “major step forward in building practical terahertz cameras”. Marketing power led Samsung, which makes CMOS camera chips and quantum dot devices, to collaborate on this research.
Conventional research for such a long time operates at the temperature of liquid helium (-452 degrees Fahrenheit), Nelson said, which is necessary to detect the extremely low energy of background terahertz photons. The fact that this new device can detect and use a visible light camera to see these wavelengths is unexpected for those working in terahertz. “People are like, ‘What?’ It’s kind of unheard of, and people are surprised,” Oh said.
According to researchers, there are many ways to improve the effect of the new camera, including further miniaturization of components and ways to protect quantum dots. Even at the current discovery stage, the device may have potential applications, they said.
As for the market potential of the new device, Nelson said that quantum dots are now cheap and fast, and are now used in consumer products such as television screens. Of course the design of the camera is complex, he says, but it depends on the current microelectronic technology. In fact, unlike the current terahertz detectors, the entire terahertz camera chip can be manufactured using modern microchip production methods, which means that eventually the production of the device should be possible and cheap.
Now, although the camera system is still far from commercial, MIT researchers are using a new laboratory device when they need a quick way to detect terahertz radiation. “We didn’t have one of those expensive cameras,” Nelson says, “but we had a lot of these little devices. People would stick one of the lights on and watch the lights go off. Visually let them know when the terahertz beam is on. … People found it really fitting.
Although terahertz waves could in principle be used to detect certain astrophysical events, these sources would be too powerful and the new device would not be able to capture the weak signals, Nelson says, though and the team is working to improve its understanding. . “Next-gen is all about making everything smaller, so it’s going to be a lot more responsive,” he says.
Terahertz radiation, whose wavelength is between microwaves and visible light, can penetrate many non-metallic materials and detect the signature of certain particles. These useful properties can lend themselves to a variety of applications, including airport digitization security, industrial quality control, astrophysical research, non-destructive object identification, and high-bandwidth wireless communications.
However, developing devices to detect and image terahertz waves has been difficult, and most existing terahertz devices are expensive, slow, bulky, and require space systems and low temperatures.
